diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt
index 820bbf3b892a..e28f7f29f2b3 100644
--- a/Documentation/trace/events.txt
+++ b/Documentation/trace/events.txt
@@ -517,1981 +517,4 @@ triggers (you have to use '!' for each one added.)
   totals derived from one or more trace event format fields and/or
   event counts (hitcount).
 
-  The format of a hist trigger is as follows:
-
-        hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>]
-          [:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue]
-          [:clear][:name=histname1] [if <filter>]
-
-  When a matching event is hit, an entry is added to a hash table
-  using the key(s) and value(s) named.  Keys and values correspond to
-  fields in the event's format description.  Values must correspond to
-  numeric fields - on an event hit, the value(s) will be added to a
-  sum kept for that field.  The special string 'hitcount' can be used
-  in place of an explicit value field - this is simply a count of
-  event hits.  If 'values' isn't specified, an implicit 'hitcount'
-  value will be automatically created and used as the only value.
-  Keys can be any field, or the special string 'stacktrace', which
-  will use the event's kernel stacktrace as the key.  The keywords
-  'keys' or 'key' can be used to specify keys, and the keywords
-  'values', 'vals', or 'val' can be used to specify values.  Compound
-  keys consisting of up to two fields can be specified by the 'keys'
-  keyword.  Hashing a compound key produces a unique entry in the
-  table for each unique combination of component keys, and can be
-  useful for providing more fine-grained summaries of event data.
-  Additionally, sort keys consisting of up to two fields can be
-  specified by the 'sort' keyword.  If more than one field is
-  specified, the result will be a 'sort within a sort': the first key
-  is taken to be the primary sort key and the second the secondary
-  key.  If a hist trigger is given a name using the 'name' parameter,
-  its histogram data will be shared with other triggers of the same
-  name, and trigger hits will update this common data.  Only triggers
-  with 'compatible' fields can be combined in this way; triggers are
-  'compatible' if the fields named in the trigger share the same
-  number and type of fields and those fields also have the same names.
-  Note that any two events always share the compatible 'hitcount' and
-  'stacktrace' fields and can therefore be combined using those
-  fields, however pointless that may be.
-
-  'hist' triggers add a 'hist' file to each event's subdirectory.
-  Reading the 'hist' file for the event will dump the hash table in
-  its entirety to stdout.  If there are multiple hist triggers
-  attached to an event, there will be a table for each trigger in the
-  output.  The table displayed for a named trigger will be the same as
-  any other instance having the same name. Each printed hash table
-  entry is a simple list of the keys and values comprising the entry;
-  keys are printed first and are delineated by curly braces, and are
-  followed by the set of value fields for the entry.  By default,
-  numeric fields are displayed as base-10 integers.  This can be
-  modified by appending any of the following modifiers to the field
-  name:
-
-        .hex        display a number as a hex value
-	.sym        display an address as a symbol
-	.sym-offset display an address as a symbol and offset
-	.syscall    display a syscall id as a system call name
-	.execname   display a common_pid as a program name
-	.usecs      display a $common_timestamp in microseconds
-
-  Note that in general the semantics of a given field aren't
-  interpreted when applying a modifier to it, but there are some
-  restrictions to be aware of in this regard:
-
-    - only the 'hex' modifier can be used for values (because values
-      are essentially sums, and the other modifiers don't make sense
-      in that context).
-    - the 'execname' modifier can only be used on a 'common_pid'.  The
-      reason for this is that the execname is simply the 'comm' value
-      saved for the 'current' process when an event was triggered,
-      which is the same as the common_pid value saved by the event
-      tracing code.  Trying to apply that comm value to other pid
-      values wouldn't be correct, and typically events that care save
-      pid-specific comm fields in the event itself.
-
-  A typical usage scenario would be the following to enable a hist
-  trigger, read its current contents, and then turn it off:
-
-  # echo 'hist:keys=skbaddr.hex:vals=len' > \
-    /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
-  # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
-
-  # echo '!hist:keys=skbaddr.hex:vals=len' > \
-    /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
-  The trigger file itself can be read to show the details of the
-  currently attached hist trigger.  This information is also displayed
-  at the top of the 'hist' file when read.
-
-  By default, the size of the hash table is 2048 entries.  The 'size'
-  parameter can be used to specify more or fewer than that.  The units
-  are in terms of hashtable entries - if a run uses more entries than
-  specified, the results will show the number of 'drops', the number
-  of hits that were ignored.  The size should be a power of 2 between
-  128 and 131072 (any non- power-of-2 number specified will be rounded
-  up).
-
-  The 'sort' parameter can be used to specify a value field to sort
-  on.  The default if unspecified is 'hitcount' and the default sort
-  order is 'ascending'.  To sort in the opposite direction, append
-  .descending' to the sort key.
-
-  The 'pause' parameter can be used to pause an existing hist trigger
-  or to start a hist trigger but not log any events until told to do
-  so.  'continue' or 'cont' can be used to start or restart a paused
-  hist trigger.
-
-  The 'clear' parameter will clear the contents of a running hist
-  trigger and leave its current paused/active state.
-
-  Note that the 'pause', 'cont', and 'clear' parameters should be
-  applied using 'append' shell operator ('>>') if applied to an
-  existing trigger, rather than via the '>' operator, which will cause
-  the trigger to be removed through truncation.
-
-- enable_hist/disable_hist
-
-  The enable_hist and disable_hist triggers can be used to have one
-  event conditionally start and stop another event's already-attached
-  hist trigger.  Any number of enable_hist and disable_hist triggers
-  can be attached to a given event, allowing that event to kick off
-  and stop aggregations on a host of other events.
-
-  The format is very similar to the enable/disable_event triggers:
-
-      enable_hist:<system>:<event>[:count]
-      disable_hist:<system>:<event>[:count]
-
-  Instead of enabling or disabling the tracing of the target event
-  into the trace buffer as the enable/disable_event triggers do, the
-  enable/disable_hist triggers enable or disable the aggregation of
-  the target event into a hash table.
-
-  A typical usage scenario for the enable_hist/disable_hist triggers
-  would be to first set up a paused hist trigger on some event,
-  followed by an enable_hist/disable_hist pair that turns the hist
-  aggregation on and off when conditions of interest are hit:
-
-  # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \
-    /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
-  # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
-    /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
-
-  # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
-    /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
-
-  The above sets up an initially paused hist trigger which is unpaused
-  and starts aggregating events when a given program is executed, and
-  which stops aggregating when the process exits and the hist trigger
-  is paused again.
-
-  The examples below provide a more concrete illustration of the
-  concepts and typical usage patterns discussed above.
-
-  'special' event fields
-  ------------------------
-
-  There are a number of 'special event fields' available for use as
-  keys or values in a hist trigger.  These look like and behave as if
-  they were actual event fields, but aren't really part of the event's
-  field definition or format file.  They are however available for any
-  event, and can be used anywhere an actual event field could be.
-  'Special' field names are always prefixed with a '$' character to
-  indicate that they're not normal fields (with the exception of
-  'cpu', for compatibility with existing filter usage):
-
-    $common_timestamp      u64 - timestamp (from ring buffer) associated
-                                 with the event, in nanoseconds.  May be
-				 modified by .usecs to have timestamps
-				 interpreted as microseconds.
-    cpu                    int - the cpu on which the event occurred.
-
-  Extended error information
-  --------------------------
-
-  For some error conditions encountered when invoking a hist trigger
-  command, extended error information is available via the
-  corresponding event's 'hist' file.  Reading the hist file after an
-  error will display more detailed information about what went wrong,
-  if information is available.  This extended error information will
-  be available until the next hist trigger command for that event.
-
-  If available for a given error condition, the extended error
-  information and usage takes the following form:
-
-    # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
-    echo: write error: Invalid argument
-
-    # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/hist
-    ERROR: Couldn't yyy: zzz
-      Last command: xxx
-
-6.2 'hist' trigger examples
----------------------------
-
-  The first set of examples creates aggregations using the kmalloc
-  event.  The fields that can be used for the hist trigger are listed
-  in the kmalloc event's format file:
-
-    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/format
-    name: kmalloc
-    ID: 374
-    format:
-	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
-	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
-	field:unsigned char common_preempt_count;		offset:3;	size:1;	signed:0;
-	field:int common_pid;					offset:4;	size:4;	signed:1;
-
-	field:unsigned long call_site;				offset:8;	size:8;	signed:0;
-	field:const void * ptr;					offset:16;	size:8;	signed:0;
-	field:size_t bytes_req;					offset:24;	size:8;	signed:0;
-	field:size_t bytes_alloc;				offset:32;	size:8;	signed:0;
-	field:gfp_t gfp_flags;					offset:40;	size:4;	signed:0;
-
-  We'll start by creating a hist trigger that generates a simple table
-  that lists the total number of bytes requested for each function in
-  the kernel that made one or more calls to kmalloc:
-
-    # echo 'hist:key=call_site:val=bytes_req' > \
-            /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
-  This tells the tracing system to create a 'hist' trigger using the
-  call_site field of the kmalloc event as the key for the table, which
-  just means that each unique call_site address will have an entry
-  created for it in the table.  The 'val=bytes_req' parameter tells
-  the hist trigger that for each unique entry (call_site) in the
-  table, it should keep a running total of the number of bytes
-  requested by that call_site.
-
-  We'll let it run for awhile and then dump the contents of the 'hist'
-  file in the kmalloc event's subdirectory (for readability, a number
-  of entries have been omitted):
-
-    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
-    # trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
-
-    { call_site: 18446744072106379007 } hitcount:          1  bytes_req:        176
-    { call_site: 18446744071579557049 } hitcount:          1  bytes_req:       1024
-    { call_site: 18446744071580608289 } hitcount:          1  bytes_req:      16384
-    { call_site: 18446744071581827654 } hitcount:          1  bytes_req:         24
-    { call_site: 18446744071580700980 } hitcount:          1  bytes_req:          8
-    { call_site: 18446744071579359876 } hitcount:          1  bytes_req:        152
-    { call_site: 18446744071580795365 } hitcount:          3  bytes_req:        144
-    { call_site: 18446744071581303129 } hitcount:          3  bytes_req:        144
-    { call_site: 18446744071580713234 } hitcount:          4  bytes_req:       2560
-    { call_site: 18446744071580933750 } hitcount:          4  bytes_req:        736
-    .
-    .
-    .
-    { call_site: 18446744072106047046 } hitcount:         69  bytes_req:       5576
-    { call_site: 18446744071582116407 } hitcount:         73  bytes_req:       2336
-    { call_site: 18446744072106054684 } hitcount:        136  bytes_req:     140504
-    { call_site: 18446744072106224230 } hitcount:        136  bytes_req:      19584
-    { call_site: 18446744072106078074 } hitcount:        153  bytes_req:       2448
-    { call_site: 18446744072106062406 } hitcount:        153  bytes_req:      36720
-    { call_site: 18446744071582507929 } hitcount:        153  bytes_req:      37088
-    { call_site: 18446744072102520590 } hitcount:        273  bytes_req:      10920
-    { call_site: 18446744071582143559 } hitcount:        358  bytes_req:        716
-    { call_site: 18446744072106465852 } hitcount:        417  bytes_req:      56712
-    { call_site: 18446744072102523378 } hitcount:        485  bytes_req:      27160
-    { call_site: 18446744072099568646 } hitcount:       1676  bytes_req:      33520
-
-    Totals:
-        Hits: 4610
-        Entries: 45
-        Dropped: 0
-
-  The output displays a line for each entry, beginning with the key
-  specified in the trigger, followed by the value(s) also specified in
-  the trigger.  At the beginning of the output is a line that displays
-  the trigger info, which can also be displayed by reading the
-  'trigger' file:
-
-    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-    hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
-
-  At the end of the output are a few lines that display the overall
-  totals for the run.  The 'Hits' field shows the total number of
-  times the event trigger was hit, the 'Entries' field shows the total
-  number of used entries in the hash table, and the 'Dropped' field
-  shows the number of hits that were dropped because the number of
-  used entries for the run exceeded the maximum number of entries
-  allowed for the table (normally 0, but if not a hint that you may
-  want to increase the size of the table using the 'size' parameter).
-
-  Notice in the above output that there's an extra field, 'hitcount',
-  which wasn't specified in the trigger.  Also notice that in the
-  trigger info output, there's a parameter, 'sort=hitcount', which
-  wasn't specified in the trigger either.  The reason for that is that
-  every trigger implicitly keeps a count of the total number of hits
-  attributed to a given entry, called the 'hitcount'.  That hitcount
-  information is explicitly displayed in the output, and in the
-  absence of a user-specified sort parameter, is used as the default
-  sort field.
-
-  The value 'hitcount' can be used in place of an explicit value in
-  the 'values' parameter if you don't really need to have any
-  particular field summed and are mainly interested in hit
-  frequencies.
-
-  To turn the hist trigger off, simply call up the trigger in the
-  command history and re-execute it with a '!' prepended:
-
-    # echo '!hist:key=call_site:val=bytes_req' > \
-           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
-  Finally, notice that the call_site as displayed in the output above
-  isn't really very useful.  It's an address, but normally addresses
-  are displayed in hex.  To have a numeric field displayed as a hex
-  value, simply append '.hex' to the field name in the trigger:
-
-    # echo 'hist:key=call_site.hex:val=bytes_req' > \
-           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
-    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
-    # trigger info: hist:keys=call_site.hex:vals=bytes_req:sort=hitcount:size=2048 [active]
-
-    { call_site: ffffffffa026b291 } hitcount:          1  bytes_req:        433
-    { call_site: ffffffffa07186ff } hitcount:          1  bytes_req:        176
-    { call_site: ffffffff811ae721 } hitcount:          1  bytes_req:      16384
-    { call_site: ffffffff811c5134 } hitcount:          1  bytes_req:          8
-    { call_site: ffffffffa04a9ebb } hitcount:          1  bytes_req:        511
-    { call_site: ffffffff8122e0a6 } hitcount:          1  bytes_req:         12
-    { call_site: ffffffff8107da84 } hitcount:          1  bytes_req:        152
-    { call_site: ffffffff812d8246 } hitcount:          1  bytes_req:         24
-    { call_site: ffffffff811dc1e5 } hitcount:          3  bytes_req:        144
-    { call_site: ffffffffa02515e8 } hitcount:          3  bytes_req:        648
-    { call_site: ffffffff81258159 } hitcount:          3  bytes_req:        144
-    { call_site: ffffffff811c80f4 } hitcount:          4  bytes_req:        544
-    .
-    .
-    .
-    { call_site: ffffffffa06c7646 } hitcount:        106  bytes_req:       8024
-    { call_site: ffffffffa06cb246 } hitcount:        132  bytes_req:      31680
-    { call_site: ffffffffa06cef7a } hitcount:        132  bytes_req:       2112
-    { call_site: ffffffff8137e399 } hitcount:        132  bytes_req:      23232
-    { call_site: ffffffffa06c941c } hitcount:        185  bytes_req:     171360
-    { call_site: ffffffffa06f2a66 } hitcount:        185  bytes_req:      26640
-    { call_site: ffffffffa036a70e } hitcount:        265  bytes_req:      10600
-    { call_site: ffffffff81325447 } hitcount:        292  bytes_req:        584
-    { call_site: ffffffffa072da3c } hitcount:        446  bytes_req:      60656
-    { call_site: ffffffffa036b1f2 } hitcount:        526  bytes_req:      29456
-    { call_site: ffffffffa0099c06 } hitcount:       1780  bytes_req:      35600
-
-    Totals:
-        Hits: 4775
-        Entries: 46
-        Dropped: 0
-
-  Even that's only marginally more useful - while hex values do look
-  more like addresses, what users are typically more interested in
-  when looking at text addresses are the corresponding symbols
-  instead.  To have an address displayed as symbolic value instead,
-  simply append '.sym' or '.sym-offset' to the field name in the
-  trigger:
-
-    # echo 'hist:key=call_site.sym:val=bytes_req' > \
-           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
-    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
-    # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=hitcount:size=2048 [active]
-
-    { call_site: [ffffffff810adcb9] syslog_print_all                              } hitcount:          1  bytes_req:       1024
-    { call_site: [ffffffff8154bc62] usb_control_msg                               } hitcount:          1  bytes_req:          8
-    { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid]                      } hitcount:          1  bytes_req:          7
-    { call_site: [ffffffff8154acbe] usb_alloc_urb                                 } hitcount:          1  bytes_req:        192
-    { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid]                     } hitcount:          1  bytes_req:          7
-    { call_site: [ffffffff811e3a25] __seq_open_private                            } hitcount:          1  bytes_req:         40
-    { call_site: [ffffffff8109524a] alloc_fair_sched_group                        } hitcount:          2  bytes_req:        128
-    { call_site: [ffffffff811febd5] fsnotify_alloc_group                          } hitcount:          2  bytes_req:        528
-    { call_site: [ffffffff81440f58] __tty_buffer_request_room                     } hitcount:          2  bytes_req:       2624
-    { call_site: [ffffffff81200ba6] inotify_new_group                             } hitcount:          2  bytes_req:         96
-    { call_site: [ffffffffa05e19af] ieee80211_start_tx_ba_session [mac80211]      } hitcount:          2  bytes_req:        464
-    { call_site: [ffffffff81672406] tcp_get_metrics                               } hitcount:          2  bytes_req:        304
-    { call_site: [ffffffff81097ec2] alloc_rt_sched_group                          } hitcount:          2  bytes_req:        128
-    { call_site: [ffffffff81089b05] sched_create_group                            } hitcount:          2  bytes_req:       1424
-    .
-    .
-    .
-    { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915]                   } hitcount:       1185  bytes_req:     123240
-    { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm]                } hitcount:       1185  bytes_req:     104280
-    { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915]            } hitcount:       1402  bytes_req:     190672
-    { call_site: [ffffffff812891ca] ext4_find_extent                              } hitcount:       1518  bytes_req:     146208
-    { call_site: [ffffffffa029070e] drm_vma_node_allow [drm]                      } hitcount:       1746  bytes_req:      69840
-    { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915]         } hitcount:       2021  bytes_req:     792312
-    { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm]                   } hitcount:       2592  bytes_req:     145152
-    { call_site: [ffffffffa0489a66] intel_ring_begin [i915]                       } hitcount:       2629  bytes_req:     378576
-    { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915]                   } hitcount:       2629  bytes_req:    3783248
-    { call_site: [ffffffff81325607] apparmor_file_alloc_security                  } hitcount:       5192  bytes_req:      10384
-    { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid]                    } hitcount:       5529  bytes_req:     110584
-    { call_site: [ffffffff8131ebf7] aa_alloc_task_context                         } hitcount:      21943  bytes_req:     702176
-    { call_site: [ffffffff8125847d] ext4_htree_store_dirent                       } hitcount:      55759  bytes_req:    5074265
-
-    Totals:
-        Hits: 109928
-        Entries: 71
-        Dropped: 0
-
-  Because the default sort key above is 'hitcount', the above shows a
-  the list of call_sites by increasing hitcount, so that at the bottom
-  we see the functions that made the most kmalloc calls during the
-  run.  If instead we we wanted to see the top kmalloc callers in
-  terms of the number of bytes requested rather than the number of
-  calls, and we wanted the top caller to appear at the top, we can use
-  the 'sort' parameter, along with the 'descending' modifier:
-
-    # echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \
-           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
-    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
-    # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
-
-    { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915]                   } hitcount:       2186  bytes_req:    3397464
-    { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915]         } hitcount:       1790  bytes_req:     712176
-    { call_site: [ffffffff8125847d] ext4_htree_store_dirent                       } hitcount:       8132  bytes_req:     513135
-    { call_site: [ffffffff811e2a1b] seq_buf_alloc                                 } hitcount:        106  bytes_req:     440128
-    { call_site: [ffffffffa0489a66] intel_ring_begin [i915]                       } hitcount:       2186  bytes_req:     314784
-    { call_site: [ffffffff812891ca] ext4_find_extent                              } hitcount:       2174  bytes_req:     208992
-    { call_site: [ffffffff811ae8e1] __kmalloc                                     } hitcount:          8  bytes_req:     131072
-    { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915]            } hitcount:        859  bytes_req:     116824
-    { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm]                   } hitcount:       1834  bytes_req:     102704
-    { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915]                   } hitcount:        972  bytes_req:     101088
-    { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm]                } hitcount:        972  bytes_req:      85536
-    { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid]                    } hitcount:       3333  bytes_req:      66664
-    { call_site: [ffffffff8137e559] sg_kmalloc                                    } hitcount:        209  bytes_req:      61632
-    .
-    .
-    .
-    { call_site: [ffffffff81095225] alloc_fair_sched_group                        } hitcount:          2  bytes_req:        128
-    { call_site: [ffffffff81097ec2] alloc_rt_sched_group                          } hitcount:          2  bytes_req:        128
-    { call_site: [ffffffff812d8406] copy_semundo                                  } hitcount:          2  bytes_req:         48
-    { call_site: [ffffffff81200ba6] inotify_new_group                             } hitcount:          1  bytes_req:         48
-    { call_site: [ffffffffa027121a] drm_getmagic [drm]                            } hitcount:          1  bytes_req:         48
-    { call_site: [ffffffff811e3a25] __seq_open_private                            } hitcount:          1  bytes_req:         40
-    { call_site: [ffffffff811c52f4] bprm_change_interp                            } hitcount:          2  bytes_req:         16
-    { call_site: [ffffffff8154bc62] usb_control_msg                               } hitcount:          1  bytes_req:          8
-    { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid]                     } hitcount:          1  bytes_req:          7
-    { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid]                      } hitcount:          1  bytes_req:          7
-
-    Totals:
-        Hits: 32133
-        Entries: 81
-        Dropped: 0
-
-  To display the offset and size information in addition to the symbol
-  name, just use 'sym-offset' instead:
-
-    # echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \
-           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
-    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
-    # trigger info: hist:keys=call_site.sym-offset:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
-
-    { call_site: [ffffffffa046041c] i915_gem_execbuffer2+0x6c/0x2c0 [i915]                  } hitcount:       4569  bytes_req:    3163720
-    { call_site: [ffffffffa0489a66] intel_ring_begin+0xc6/0x1f0 [i915]                      } hitcount:       4569  bytes_req:     657936
-    { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23+0x694/0x1020 [i915]      } hitcount:       1519  bytes_req:     472936
-    { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23+0x516/0x1020 [i915]      } hitcount:       3050  bytes_req:     211832
-    { call_site: [ffffffff811e2a1b] seq_buf_alloc+0x1b/0x50                                 } hitcount:         34  bytes_req:     148384
-    { call_site: [ffffffffa04a580c] intel_crtc_page_flip+0xbc/0x870 [i915]                  } hitcount:       1385  bytes_req:     144040
-    { call_site: [ffffffff811ae8e1] __kmalloc+0x191/0x1b0                                   } hitcount:          8  bytes_req:     131072
-    { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl+0x282/0x360 [drm]              } hitcount:       1385  bytes_req:     121880
-    { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc+0x32/0x100 [drm]                  } hitcount:       1848  bytes_req:     103488
-    { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state+0x2c/0xa0 [i915]            } hitcount:        461  bytes_req:      62696
-    { call_site: [ffffffffa029070e] drm_vma_node_allow+0x2e/0xd0 [drm]                      } hitcount:       1541  bytes_req:      61640
-    { call_site: [ffffffff815f8d7b] sk_prot_alloc+0xcb/0x1b0                                } hitcount:         57  bytes_req:      57456
-    .
-    .
-    .
-    { call_site: [ffffffff8109524a] alloc_fair_sched_group+0x5a/0x1a0                       } hitcount:          2  bytes_req:        128
-    { call_site: [ffffffffa027b921] drm_vm_open_locked+0x31/0xa0 [drm]                      } hitcount:          3  bytes_req:         96
-    { call_site: [ffffffff8122e266] proc_self_follow_link+0x76/0xb0                         } hitcount:          8  bytes_req:         96
-    { call_site: [ffffffff81213e80] load_elf_binary+0x240/0x1650                            } hitcount:          3  bytes_req:         84
-    { call_site: [ffffffff8154bc62] usb_control_msg+0x42/0x110                              } hitcount:          1  bytes_req:          8
-    { call_site: [ffffffffa00bf6fe] hidraw_send_report+0x7e/0x1a0 [hid]                     } hitcount:          1  bytes_req:          7
-    { call_site: [ffffffffa00bf1ca] hidraw_report_event+0x8a/0x120 [hid]                    } hitcount:          1  bytes_req:          7
-
-    Totals:
-        Hits: 26098
-        Entries: 64
-        Dropped: 0
-
-  We can also add multiple fields to the 'values' parameter.  For
-  example, we might want to see the total number of bytes allocated
-  alongside bytes requested, and display the result sorted by bytes
-  allocated in a descending order:
-
-    # echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \
-           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
-    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
-    # trigger info: hist:keys=call_site.sym:vals=bytes_req,bytes_alloc:sort=bytes_alloc.descending:size=2048 [active]
-
-    { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915]                   } hitcount:       7403  bytes_req:    4084360  bytes_alloc:    5958016
-    { call_site: [ffffffff811e2a1b] seq_buf_alloc                                 } hitcount:        541  bytes_req:    2213968  bytes_alloc:    2228224
-    { call_site: [ffffffffa0489a66] intel_ring_begin [i915]                       } hitcount:       7404  bytes_req:    1066176  bytes_alloc:    1421568
-    { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915]         } hitcount:       1565  bytes_req:     557368  bytes_alloc:    1037760
-    { call_site: [ffffffff8125847d] ext4_htree_store_dirent                       } hitcount:       9557  bytes_req:     595778  bytes_alloc:     695744
-    { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23 [i915]         } hitcount:       5839  bytes_req:     430680  bytes_alloc:     470400
-    { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915]            } hitcount:       2388  bytes_req:     324768  bytes_alloc:     458496
-    { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm]                   } hitcount:       3911  bytes_req:     219016  bytes_alloc:     250304
-    { call_site: [ffffffff815f8d7b] sk_prot_alloc                                 } hitcount:        235  bytes_req:     236880  bytes_alloc:     240640
-    { call_site: [ffffffff8137e559] sg_kmalloc                                    } hitcount:        557  bytes_req:     169024  bytes_alloc:     221760
-    { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid]                    } hitcount:       9378  bytes_req:     187548  bytes_alloc:     206312
-    { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915]                   } hitcount:       1519  bytes_req:     157976  bytes_alloc:     194432
-    .
-    .
-    .
-    { call_site: [ffffffff8109bd3b] sched_autogroup_create_attach                 } hitcount:          2  bytes_req:        144  bytes_alloc:        192
-    { call_site: [ffffffff81097ee8] alloc_rt_sched_group                          } hitcount:          2  bytes_req:        128  bytes_alloc:        128
-    { call_site: [ffffffff8109524a] alloc_fair_sched_group                        } hitcount:          2  bytes_req:        128  bytes_alloc:        128
-    { call_site: [ffffffff81095225] alloc_fair_sched_group                        } hitcount:          2  bytes_req:        128  bytes_alloc:        128
-    { call_site: [ffffffff81097ec2] alloc_rt_sched_group                          } hitcount:          2  bytes_req:        128  bytes_alloc:        128
-    { call_site: [ffffffff81213e80] load_elf_binary                               } hitcount:          3  bytes_req:         84  bytes_alloc:         96
-    { call_site: [ffffffff81079a2e] kthread_create_on_node                        } hitcount:          1  bytes_req:         56  bytes_alloc:         64
-    { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid]                      } hitcount:          1  bytes_req:          7  bytes_alloc:          8
-    { call_site: [ffffffff8154bc62] usb_control_msg                               } hitcount:          1  bytes_req:          8  bytes_alloc:          8
-    { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid]                     } hitcount:          1  bytes_req:          7  bytes_alloc:          8
-
-    Totals:
-        Hits: 66598
-        Entries: 65
-        Dropped: 0
-
-  Finally, to finish off our kmalloc example, instead of simply having
-  the hist trigger display symbolic call_sites, we can have the hist
-  trigger additionally display the complete set of kernel stack traces
-  that led to each call_site.  To do that, we simply use the special
-  value 'stacktrace' for the key parameter:
-
-    # echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \
-           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
-  The above trigger will use the kernel stack trace in effect when an
-  event is triggered as the key for the hash table.  This allows the
-  enumeration of every kernel callpath that led up to a particular
-  event, along with a running total of any of the event fields for
-  that event.  Here we tally bytes requested and bytes allocated for
-  every callpath in the system that led up to a kmalloc (in this case
-  every callpath to a kmalloc for a kernel compile):
-
-    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
-    # trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active]
-
-    { stacktrace:
-         __kmalloc_track_caller+0x10b/0x1a0
-         kmemdup+0x20/0x50
-         hidraw_report_event+0x8a/0x120 [hid]
-         hid_report_raw_event+0x3ea/0x440 [hid]
-         hid_input_report+0x112/0x190 [hid]
-         hid_irq_in+0xc2/0x260 [usbhid]
-         __usb_hcd_giveback_urb+0x72/0x120
-         usb_giveback_urb_bh+0x9e/0xe0
-         tasklet_hi_action+0xf8/0x100
-         __do_softirq+0x114/0x2c0
-         irq_exit+0xa5/0xb0
-         do_IRQ+0x5a/0xf0
-         ret_from_intr+0x0/0x30
-         cpuidle_enter+0x17/0x20
-         cpu_startup_entry+0x315/0x3e0
-         rest_init+0x7c/0x80
-    } hitcount:          3  bytes_req:         21  bytes_alloc:         24
-    { stacktrace:
-         __kmalloc_track_caller+0x10b/0x1a0
-         kmemdup+0x20/0x50
-         hidraw_report_event+0x8a/0x120 [hid]
-         hid_report_raw_event+0x3ea/0x440 [hid]
-         hid_input_report+0x112/0x190 [hid]
-         hid_irq_in+0xc2/0x260 [usbhid]
-         __usb_hcd_giveback_urb+0x72/0x120
-         usb_giveback_urb_bh+0x9e/0xe0
-         tasklet_hi_action+0xf8/0x100
-         __do_softirq+0x114/0x2c0
-         irq_exit+0xa5/0xb0
-         do_IRQ+0x5a/0xf0
-         ret_from_intr+0x0/0x30
-    } hitcount:          3  bytes_req:         21  bytes_alloc:         24
-    { stacktrace:
-         kmem_cache_alloc_trace+0xeb/0x150
-         aa_alloc_task_context+0x27/0x40
-         apparmor_cred_prepare+0x1f/0x50
-         security_prepare_creds+0x16/0x20
-         prepare_creds+0xdf/0x1a0
-         SyS_capset+0xb5/0x200
-         system_call_fastpath+0x12/0x6a
-    } hitcount:          1  bytes_req:         32  bytes_alloc:         32
-    .
-    .
-    .
-    { stacktrace:
-         __kmalloc+0x11b/0x1b0
-         i915_gem_execbuffer2+0x6c/0x2c0 [i915]
-         drm_ioctl+0x349/0x670 [drm]
-         do_vfs_ioctl+0x2f0/0x4f0
-         SyS_ioctl+0x81/0xa0
-         system_call_fastpath+0x12/0x6a
-    } hitcount:      17726  bytes_req:   13944120  bytes_alloc:   19593808
-    { stacktrace:
-         __kmalloc+0x11b/0x1b0
-         load_elf_phdrs+0x76/0xa0
-         load_elf_binary+0x102/0x1650
-         search_binary_handler+0x97/0x1d0
-         do_execveat_common.isra.34+0x551/0x6e0
-         SyS_execve+0x3a/0x50
-         return_from_execve+0x0/0x23
-    } hitcount:      33348  bytes_req:   17152128  bytes_alloc:   20226048
-    { stacktrace:
-         kmem_cache_alloc_trace+0xeb/0x150
-         apparmor_file_alloc_security+0x27/0x40
-         security_file_alloc+0x16/0x20
-         get_empty_filp+0x93/0x1c0
-         path_openat+0x31/0x5f0
-         do_filp_open+0x3a/0x90
-         do_sys_open+0x128/0x220
-         SyS_open+0x1e/0x20
-         system_call_fastpath+0x12/0x6a
-    } hitcount:    4766422  bytes_req:    9532844  bytes_alloc:   38131376
-    { stacktrace:
-         __kmalloc+0x11b/0x1b0
-         seq_buf_alloc+0x1b/0x50
-         seq_read+0x2cc/0x370
-         proc_reg_read+0x3d/0x80
-         __vfs_read+0x28/0xe0
-         vfs_read+0x86/0x140
-         SyS_read+0x46/0xb0
-         system_call_fastpath+0x12/0x6a
-    } hitcount:      19133  bytes_req:   78368768  bytes_alloc:   78368768
-
-    Totals:
-        Hits: 6085872
-        Entries: 253
-        Dropped: 0
-
-  If you key a hist trigger on common_pid, in order for example to
-  gather and display sorted totals for each process, you can use the
-  special .execname modifier to display the executable names for the
-  processes in the table rather than raw pids.  The example below
-  keeps a per-process sum of total bytes read:
-
-    # echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \
-           /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
-
-    # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/hist
-    # trigger info: hist:keys=common_pid.execname:vals=count:sort=count.descending:size=2048 [active]
-
-    { common_pid: gnome-terminal  [      3196] } hitcount:        280  count:    1093512
-    { common_pid: Xorg            [      1309] } hitcount:        525  count:     256640
-    { common_pid: compiz          [      2889] } hitcount:         59  count:     254400
-    { common_pid: bash            [      8710] } hitcount:          3  count:      66369
-    { common_pid: dbus-daemon-lau [      8703] } hitcount:         49  count:      47739
-    { common_pid: irqbalance      [      1252] } hitcount:         27  count:      27648
-    { common_pid: 01ifupdown      [      8705] } hitcount:          3  count:      17216
-    { common_pid: dbus-daemon     [       772] } hitcount:         10  count:      12396
-    { common_pid: Socket Thread   [      8342] } hitcount:         11  count:      11264
-    { common_pid: nm-dhcp-client. [      8701] } hitcount:          6  count:       7424
-    { common_pid: gmain           [      1315] } hitcount:         18  count:       6336
-    .
-    .
-    .
-    { common_pid: postgres        [      1892] } hitcount:          2  count:         32
-    { common_pid: postgres        [      1891] } hitcount:          2  count:         32
-    { common_pid: gmain           [      8704] } hitcount:          2  count:         32
-    { common_pid: upstart-dbus-br [      2740] } hitcount:         21  count:         21
-    { common_pid: nm-dispatcher.a [      8696] } hitcount:          1  count:         16
-    { common_pid: indicator-datet [      2904] } hitcount:          1  count:         16
-    { common_pid: gdbus           [      2998] } hitcount:          1  count:         16
-    { common_pid: rtkit-daemon    [      2052] } hitcount:          1  count:          8
-    { common_pid: init            [         1] } hitcount:          2  count:          2
-
-    Totals:
-        Hits: 2116
-        Entries: 51
-        Dropped: 0
-
-  Similarly, if you key a hist trigger on syscall id, for example to
-  gather and display a list of systemwide syscall hits, you can use
-  the special .syscall modifier to display the syscall names rather
-  than raw ids.  The example below keeps a running total of syscall
-  counts for the system during the run:
-
-    # echo 'hist:key=id.syscall:val=hitcount' > \
-           /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
-
-    # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
-    # trigger info: hist:keys=id.syscall:vals=hitcount:sort=hitcount:size=2048 [active]
-
-    { id: sys_fsync                     [ 74] } hitcount:          1
-    { id: sys_newuname                  [ 63] } hitcount:          1
-    { id: sys_prctl                     [157] } hitcount:          1
-    { id: sys_statfs                    [137] } hitcount:          1
-    { id: sys_symlink                   [ 88] } hitcount:          1
-    { id: sys_sendmmsg                  [307] } hitcount:          1
-    { id: sys_semctl                    [ 66] } hitcount:          1
-    { id: sys_readlink                  [ 89] } hitcount:          3
-    { id: sys_bind                      [ 49] } hitcount:          3
-    { id: sys_getsockname               [ 51] } hitcount:          3
-    { id: sys_unlink                    [ 87] } hitcount:          3
-    { id: sys_rename                    [ 82] } hitcount:          4
-    { id: unknown_syscall               [ 58] } hitcount:          4
-    { id: sys_connect                   [ 42] } hitcount:          4
-    { id: sys_getpid                    [ 39] } hitcount:          4
-    .
-    .
-    .
-    { id: sys_rt_sigprocmask            [ 14] } hitcount:        952
-    { id: sys_futex                     [202] } hitcount:       1534
-    { id: sys_write                     [  1] } hitcount:       2689
-    { id: sys_setitimer                 [ 38] } hitcount:       2797
-    { id: sys_read                      [  0] } hitcount:       3202
-    { id: sys_select                    [ 23] } hitcount:       3773
-    { id: sys_writev                    [ 20] } hitcount:       4531
-    { id: sys_poll                      [  7] } hitcount:       8314
-    { id: sys_recvmsg                   [ 47] } hitcount:      13738
-    { id: sys_ioctl                     [ 16] } hitcount:      21843
-
-    Totals:
-        Hits: 67612
-        Entries: 72
-        Dropped: 0
-
-    The syscall counts above provide a rough overall picture of system
-    call activity on the system; we can see for example that the most
-    popular system call on this system was the 'sys_ioctl' system call.
-
-    We can use 'compound' keys to refine that number and provide some
-    further insight as to which processes exactly contribute to the
-    overall ioctl count.
-
-    The command below keeps a hitcount for every unique combination of
-    system call id and pid - the end result is essentially a table
-    that keeps a per-pid sum of system call hits.  The results are
-    sorted using the system call id as the primary key, and the
-    hitcount sum as the secondary key:
-
-    # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \
-           /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
-
-    # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
-    # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active]
-
-    { id: sys_read                      [  0], common_pid: rtkit-daemon    [      1877] } hitcount:          1
-    { id: sys_read                      [  0], common_pid: gdbus           [      2976] } hitcount:          1
-    { id: sys_read                      [  0], common_pid: console-kit-dae [      3400] } hitcount:          1
-    { id: sys_read                      [  0], common_pid: postgres        [      1865] } hitcount:          1
-    { id: sys_read                      [  0], common_pid: deja-dup-monito [      3543] } hitcount:          2
-    { id: sys_read                      [  0], common_pid: NetworkManager  [       890] } hitcount:          2
-    { id: sys_read                      [  0], common_pid: evolution-calen [      3048] } hitcount:          2
-    { id: sys_read                      [  0], common_pid: postgres        [      1864] } hitcount:          2
-    { id: sys_read                      [  0], common_pid: nm-applet       [      3022] } hitcount:          2
-    { id: sys_read                      [  0], common_pid: whoopsie        [      1212] } hitcount:          2
-    .
-    .
-    .
-    { id: sys_ioctl                     [ 16], common_pid: bash            [      8479] } hitcount:          1
-    { id: sys_ioctl                     [ 16], common_pid: bash            [      3472] } hitcount:         12
-    { id: sys_ioctl                     [ 16], common_pid: gnome-terminal  [      3199] } hitcount:         16
-    { id: sys_ioctl                     [ 16], common_pid: Xorg            [      1267] } hitcount:       1808
-    { id: sys_ioctl                     [ 16], common_pid: compiz          [      2994] } hitcount:       5580
-    .
-    .
-    .
-    { id: sys_waitid                    [247], common_pid: upstart-dbus-br [      2690] } hitcount:          3
-    { id: sys_waitid                    [247], common_pid: upstart-dbus-br [      2688] } hitcount:         16
-    { id: sys_inotify_add_watch         [254], common_pid: gmain           [       975] } hitcount:          2
-    { id: sys_inotify_add_watch         [254], common_pid: gmain           [      3204] } hitcount:          4
-    { id: sys_inotify_add_watch         [254], common_pid: gmain           [      2888] } hitcount:          4
-    { id: sys_inotify_add_watch         [254], common_pid: gmain           [      3003] } hitcount:          4
-    { id: sys_inotify_add_watch         [254], common_pid: gmain           [      2873] } hitcount:          4
-    { id: sys_inotify_add_watch         [254], common_pid: gmain           [      3196] } hitcount:          6
-    { id: sys_openat                    [257], common_pid: java            [      2623] } hitcount:          2
-    { id: sys_eventfd2                  [290], common_pid: ibus-ui-gtk3    [      2760] } hitcount:          4
-    { id: sys_eventfd2                  [290], common_pid: compiz          [      2994] } hitcount:          6
-
-    Totals:
-        Hits: 31536
-        Entries: 323
-        Dropped: 0
-
-    The above list does give us a breakdown of the ioctl syscall by
-    pid, but it also gives us quite a bit more than that, which we
-    don't really care about at the moment.  Since we know the syscall
-    id for sys_ioctl (16, displayed next to the sys_ioctl name), we
-    can use that to filter out all the other syscalls:
-
-    # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \
-           /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
-
-    # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
-    # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active]
-
-    { id: sys_ioctl                     [ 16], common_pid: gmain           [      2769] } hitcount:          1
-    { id: sys_ioctl                     [ 16], common_pid: evolution-addre [      8571] } hitcount:          1
-    { id: sys_ioctl                     [ 16], common_pid: gmain           [      3003] } hitcount:          1
-    { id: sys_ioctl                     [ 16], common_pid: gmain           [      2781] } hitcount:          1
-    { id: sys_ioctl                     [ 16], common_pid: gmain           [      2829] } hitcount:          1
-    { id: sys_ioctl                     [ 16], common_pid: bash            [      8726] } hitcount:          1
-    { id: sys_ioctl                     [ 16], common_pid: bash            [      8508] } hitcount:          1
-    { id: sys_ioctl                     [ 16], common_pid: gmain           [      2970] } hitcount:          1
-    { id: sys_ioctl                     [ 16], common_pid: gmain           [      2768] } hitcount:          1
-    .
-    .
-    .
-    { id: sys_ioctl                     [ 16], common_pid: pool            [      8559] } hitcount:         45
-    { id: sys_ioctl                     [ 16], common_pid: pool            [      8555] } hitcount:         48
-    { id: sys_ioctl                     [ 16], common_pid: pool            [      8551] } hitcount:         48
-    { id: sys_ioctl                     [ 16], common_pid: avahi-daemon    [       896] } hitcount:         66
-    { id: sys_ioctl                     [ 16], common_pid: Xorg            [      1267] } hitcount:      26674
-    { id: sys_ioctl                     [ 16], common_pid: compiz          [      2994] } hitcount:      73443
-
-    Totals:
-        Hits: 101162
-        Entries: 103
-        Dropped: 0
-
-    The above output shows that 'compiz' and 'Xorg' are far and away
-    the heaviest ioctl callers (which might lead to questions about
-    whether they really need to be making all those calls and to
-    possible avenues for further investigation.)
-
-    The compound key examples used a key and a sum value (hitcount) to
-    sort the output, but we can just as easily use two keys instead.
-    Here's an example where we use a compound key composed of the the
-    common_pid and size event fields.  Sorting with pid as the primary
-    key and 'size' as the secondary key allows us to display an
-    ordered summary of the recvfrom sizes, with counts, received by
-    each process:
-
-    # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \
-           /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger
-
-    # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist
-    # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active]
-
-    { common_pid: smbd            [       784], size:          4 } hitcount:          1
-    { common_pid: dnsmasq         [      1412], size:       4096 } hitcount:        672
-    { common_pid: postgres        [      1796], size:       1000 } hitcount:          6
-    { common_pid: postgres        [      1867], size:       1000 } hitcount:         10
-    { common_pid: bamfdaemon      [      2787], size:         28 } hitcount:          2
-    { common_pid: bamfdaemon      [      2787], size:      14360 } hitcount:          1
-    { common_pid: compiz          [      2994], size:          8 } hitcount:          1
-    { common_pid: compiz          [      2994], size:         20 } hitcount:         11
-    { common_pid: gnome-terminal  [      3199], size:          4 } hitcount:          2
-    { common_pid: firefox         [      8817], size:          4 } hitcount:          1
-    { common_pid: firefox         [      8817], size:          8 } hitcount:          5
-    { common_pid: firefox         [      8817], size:        588 } hitcount:          2
-    { common_pid: firefox         [      8817], size:        628 } hitcount:          1
-    { common_pid: firefox         [      8817], size:       6944 } hitcount:          1
-    { common_pid: firefox         [      8817], size:     408880 } hitcount:          2
-    { common_pid: firefox         [      8822], size:          8 } hitcount:          2
-    { common_pid: firefox         [      8822], size:        160 } hitcount:          2
-    { common_pid: firefox         [      8822], size:        320 } hitcount:          2
-    { common_pid: firefox         [      8822], size:        352 } hitcount:          1
-    .
-    .
-    .
-    { common_pid: pool            [      8923], size:       1960 } hitcount:         10
-    { common_pid: pool            [      8923], size:       2048 } hitcount:         10
-    { common_pid: pool            [      8924], size:       1960 } hitcount:         10
-    { common_pid: pool            [      8924], size:       2048 } hitcount:         10
-    { common_pid: pool            [      8928], size:       1964 } hitcount:          4
-    { common_pid: pool            [      8928], size:       1965 } hitcount:          2
-    { common_pid: pool            [      8928], size:       2048 } hitcount:          6
-    { common_pid: pool            [      8929], size:       1982 } hitcount:          1
-    { common_pid: pool            [      8929], size:       2048 } hitcount:          1
-
-    Totals:
-        Hits: 2016
-        Entries: 224
-        Dropped: 0
-
-  The above example also illustrates the fact that although a compound
-  key is treated as a single entity for hashing purposes, the sub-keys
-  it's composed of can be accessed independently.
-
-  The next example uses a string field as the hash key and
-  demonstrates how you can manually pause and continue a hist trigger.
-  In this example, we'll aggregate fork counts and don't expect a
-  large number of entries in the hash table, so we'll drop it to a
-  much smaller number, say 256:
-
-    # echo 'hist:key=child_comm:val=hitcount:size=256' > \
-           /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
-
-    # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
-    # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
-
-    { child_comm: dconf worker                        } hitcount:          1
-    { child_comm: ibus-daemon                         } hitcount:          1
-    { child_comm: whoopsie                            } hitcount:          1
-    { child_comm: smbd                                } hitcount:          1
-    { child_comm: gdbus                               } hitcount:          1
-    { child_comm: kthreadd                            } hitcount:          1
-    { child_comm: dconf worker                        } hitcount:          1
-    { child_comm: evolution-alarm                     } hitcount:          2
-    { child_comm: Socket Thread                       } hitcount:          2
-    { child_comm: postgres                            } hitcount:          2
-    { child_comm: bash                                } hitcount:          3
-    { child_comm: compiz                              } hitcount:          3
-    { child_comm: evolution-sourc                     } hitcount:          4
-    { child_comm: dhclient                            } hitcount:          4
-    { child_comm: pool                                } hitcount:          5
-    { child_comm: nm-dispatcher.a                     } hitcount:          8
-    { child_comm: firefox                             } hitcount:          8
-    { child_comm: dbus-daemon                         } hitcount:          8
-    { child_comm: glib-pacrunner                      } hitcount:         10
-    { child_comm: evolution                           } hitcount:         23
-
-    Totals:
-        Hits: 89
-        Entries: 20
-        Dropped: 0
-
-  If we want to pause the hist trigger, we can simply append :pause to
-  the command that started the trigger.  Notice that the trigger info
-  displays as [paused]:
-
-    # echo 'hist:key=child_comm:val=hitcount:size=256:pause' >> \
-           /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
-
-    # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
-    # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [paused]
-
-    { child_comm: dconf worker                        } hitcount:          1
-    { child_comm: kthreadd                            } hitcount:          1
-    { child_comm: dconf worker                        } hitcount:          1
-    { child_comm: gdbus                               } hitcount:          1
-    { child_comm: ibus-daemon                         } hitcount:          1
-    { child_comm: Socket Thread                       } hitcount:          2
-    { child_comm: evolution-alarm                     } hitcount:          2
-    { child_comm: smbd                                } hitcount:          2
-    { child_comm: bash                                } hitcount:          3
-    { child_comm: whoopsie                            } hitcount:          3
-    { child_comm: compiz                              } hitcount:          3
-    { child_comm: evolution-sourc                     } hitcount:          4
-    { child_comm: pool                                } hitcount:          5
-    { child_comm: postgres                            } hitcount:          6
-    { child_comm: firefox                             } hitcount:          8
-    { child_comm: dhclient                            } hitcount:         10
-    { child_comm: emacs                               } hitcount:         12
-    { child_comm: dbus-daemon                         } hitcount:         20
-    { child_comm: nm-dispatcher.a                     } hitcount:         20
-    { child_comm: evolution                           } hitcount:         35
-    { child_comm: glib-pacrunner                      } hitcount:         59
-
-    Totals:
-        Hits: 199
-        Entries: 21
-        Dropped: 0
-
-  To manually continue having the trigger aggregate events, append
-  :cont instead.  Notice that the trigger info displays as [active]
-  again, and the data has changed:
-
-    # echo 'hist:key=child_comm:val=hitcount:size=256:cont' >> \
-           /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
-
-    # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
-    # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
-
-    { child_comm: dconf worker                        } hitcount:          1
-    { child_comm: dconf worker                        } hitcount:          1
-    { child_comm: kthreadd                            } hitcount:          1
-    { child_comm: gdbus                               } hitcount:          1
-    { child_comm: ibus-daemon                         } hitcount:          1
-    { child_comm: Socket Thread                       } hitcount:          2
-    { child_comm: evolution-alarm                     } hitcount:          2
-    { child_comm: smbd                                } hitcount:          2
-    { child_comm: whoopsie                            } hitcount:          3
-    { child_comm: compiz                              } hitcount:          3
-    { child_comm: evolution-sourc                     } hitcount:          4
-    { child_comm: bash                                } hitcount:          5
-    { child_comm: pool                                } hitcount:          5
-    { child_comm: postgres                            } hitcount:          6
-    { child_comm: firefox                             } hitcount:          8
-    { child_comm: dhclient                            } hitcount:         11
-    { child_comm: emacs                               } hitcount:         12
-    { child_comm: dbus-daemon                         } hitcount:         22
-    { child_comm: nm-dispatcher.a                     } hitcount:         22
-    { child_comm: evolution                           } hitcount:         35
-    { child_comm: glib-pacrunner                      } hitcount:         59
-
-    Totals:
-        Hits: 206
-        Entries: 21
-        Dropped: 0
-
-  The previous example showed how to start and stop a hist trigger by
-  appending 'pause' and 'continue' to the hist trigger command.  A
-  hist trigger can also be started in a paused state by initially
-  starting the trigger with ':pause' appended.  This allows you to
-  start the trigger only when you're ready to start collecting data
-  and not before.  For example, you could start the trigger in a
-  paused state, then unpause it and do something you want to measure,
-  then pause the trigger again when done.
-
-  Of course, doing this manually can be difficult and error-prone, but
-  it is possible to automatically start and stop a hist trigger based
-  on some condition, via the enable_hist and disable_hist triggers.
-
-  For example, suppose we wanted to take a look at the relative
-  weights in terms of skb length for each callpath that leads to a
-  netif_receieve_skb event when downloading a decent-sized file using
-  wget.
-
-  First we set up an initially paused stacktrace trigger on the
-  netif_receive_skb event:
-
-    # echo 'hist:key=stacktrace:vals=len:pause' > \
-           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
-  Next, we set up an 'enable_hist' trigger on the sched_process_exec
-  event, with an 'if filename==/usr/bin/wget' filter.  The effect of
-  this new trigger is that it will 'unpause' the hist trigger we just
-  set up on netif_receive_skb if and only if it sees a
-  sched_process_exec event with a filename of '/usr/bin/wget'.  When
-  that happens, all netif_receive_skb events are aggregated into a
-  hash table keyed on stacktrace:
-
-    # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
-           /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
-
-  The aggregation continues until the netif_receive_skb is paused
-  again, which is what the following disable_hist event does by
-  creating a similar setup on the sched_process_exit event, using the
-  filter 'comm==wget':
-
-    # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
-           /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
-
-  Whenever a process exits and the comm field of the disable_hist
-  trigger filter matches 'comm==wget', the netif_receive_skb hist
-  trigger is disabled.
-
-  The overall effect is that netif_receive_skb events are aggregated
-  into the hash table for only the duration of the wget.  Executing a
-  wget command and then listing the 'hist' file will display the
-  output generated by the wget command:
-
-    $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
-
-    # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
-    # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
-
-    { stacktrace:
-         __netif_receive_skb_core+0x46d/0x990
-         __netif_receive_skb+0x18/0x60
-         netif_receive_skb_internal+0x23/0x90
-         napi_gro_receive+0xc8/0x100
-         ieee80211_deliver_skb+0xd6/0x270 [mac80211]
-         ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
-         ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
-         ieee80211_rx+0x31d/0x900 [mac80211]
-         iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
-         iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
-         iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
-         irq_thread_fn+0x20/0x50
-         irq_thread+0x11f/0x150
-         kthread+0xd2/0xf0
-         ret_from_fork+0x42/0x70
-    } hitcount:         85  len:      28884
-    { stacktrace:
-         __netif_receive_skb_core+0x46d/0x990
-         __netif_receive_skb+0x18/0x60
-         netif_receive_skb_internal+0x23/0x90
-         napi_gro_complete+0xa4/0xe0
-         dev_gro_receive+0x23a/0x360
-         napi_gro_receive+0x30/0x100
-         ieee80211_deliver_skb+0xd6/0x270 [mac80211]
-         ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
-         ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
-         ieee80211_rx+0x31d/0x900 [mac80211]
-         iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
-         iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
-         iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
-         irq_thread_fn+0x20/0x50
-         irq_thread+0x11f/0x150
-         kthread+0xd2/0xf0
-    } hitcount:         98  len:     664329
-    { stacktrace:
-         __netif_receive_skb_core+0x46d/0x990
-         __netif_receive_skb+0x18/0x60
-         process_backlog+0xa8/0x150
-         net_rx_action+0x15d/0x340
-         __do_softirq+0x114/0x2c0
-         do_softirq_own_stack+0x1c/0x30
-         do_softirq+0x65/0x70
-         __local_bh_enable_ip+0xb5/0xc0
-         ip_finish_output+0x1f4/0x840
-         ip_output+0x6b/0xc0
-         ip_local_out_sk+0x31/0x40
-         ip_send_skb+0x1a/0x50
-         udp_send_skb+0x173/0x2a0
-         udp_sendmsg+0x2bf/0x9f0
-         inet_sendmsg+0x64/0xa0
-         sock_sendmsg+0x3d/0x50
-    } hitcount:        115  len:      13030
-    { stacktrace:
-         __netif_receive_skb_core+0x46d/0x990
-         __netif_receive_skb+0x18/0x60
-         netif_receive_skb_internal+0x23/0x90
-         napi_gro_complete+0xa4/0xe0
-         napi_gro_flush+0x6d/0x90
-         iwl_pcie_irq_handler+0x92a/0x12f0 [iwlwifi]
-         irq_thread_fn+0x20/0x50
-         irq_thread+0x11f/0x150
-         kthread+0xd2/0xf0
-         ret_from_fork+0x42/0x70
-    } hitcount:        934  len:    5512212
-
-    Totals:
-        Hits: 1232
-        Entries: 4
-        Dropped: 0
-
-  The above shows all the netif_receive_skb callpaths and their total
-  lengths for the duration of the wget command.
-
-  The 'clear' hist trigger param can be used to clear the hash table.
-  Suppose we wanted to try another run of the previous example but
-  this time also wanted to see the complete list of events that went
-  into the histogram.  In order to avoid having to set everything up
-  again, we can just clear the histogram first:
-
-    # echo 'hist:key=stacktrace:vals=len:clear' >> \
-           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
-  Just to verify that it is in fact cleared, here's what we now see in
-  the hist file:
-
-    # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
-    # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
-
-    Totals:
-        Hits: 0
-        Entries: 0
-        Dropped: 0
-
-  Since we want to see the detailed list of every netif_receive_skb
-  event occurring during the new run, which are in fact the same
-  events being aggregated into the hash table, we add some additional
-  'enable_event' events to the triggering sched_process_exec and
-  sched_process_exit events as such:
-
-    # echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \
-           /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
-
-    # echo 'disable_event:net:netif_receive_skb if comm==wget' > \
-           /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
-
-  If you read the trigger files for the sched_process_exec and
-  sched_process_exit triggers, you should see two triggers for each:
-  one enabling/disabling the hist aggregation and the other
-  enabling/disabling the logging of events:
-
-    # cat /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
-    enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
-    enable_hist:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
-
-    # cat /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
-    enable_event:net:netif_receive_skb:unlimited if comm==wget
-    disable_hist:net:netif_receive_skb:unlimited if comm==wget
-
-  In other words, whenever either of the sched_process_exec or
-  sched_process_exit events is hit and matches 'wget', it enables or
-  disables both the histogram and the event log, and what you end up
-  with is a hash table and set of events just covering the specified
-  duration.  Run the wget command again:
-
-    $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
-
-  Displaying the 'hist' file should show something similar to what you
-  saw in the last run, but this time you should also see the
-  individual events in the trace file:
-
-    # cat /sys/kernel/debug/tracing/trace
-
-    # tracer: nop
-    #
-    # entries-in-buffer/entries-written: 183/1426   #P:4
-    #
-    #                              _-----=> irqs-off
-    #                             / _----=> need-resched
-    #                            | / _---=> hardirq/softirq
-    #                            || / _--=> preempt-depth
-    #                            ||| /     delay
-    #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
-    #              | |       |   ||||       |         |
-                wget-15108 [000] ..s1 31769.606929: netif_receive_skb: dev=lo skbaddr=ffff88009c353100 len=60
-                wget-15108 [000] ..s1 31769.606999: netif_receive_skb: dev=lo skbaddr=ffff88009c353200 len=60
-             dnsmasq-1382  [000] ..s1 31769.677652: netif_receive_skb: dev=lo skbaddr=ffff88009c352b00 len=130
-             dnsmasq-1382  [000] ..s1 31769.685917: netif_receive_skb: dev=lo skbaddr=ffff88009c352200 len=138
-    ##### CPU 2 buffer started ####
-      irq/29-iwlwifi-559   [002] ..s. 31772.031529: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433d00 len=2948
-      irq/29-iwlwifi-559   [002] ..s. 31772.031572: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432200 len=1500
-      irq/29-iwlwifi-559   [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948
-      irq/29-iwlwifi-559   [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948
-      irq/29-iwlwifi-559   [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500
-    .
-    .
-    .
-
-  The following example demonstrates how multiple hist triggers can be
-  attached to a given event.  This capability can be useful for
-  creating a set of different summaries derived from the same set of
-  events, or for comparing the effects of different filters, among
-  other things.
-
-    # echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \
-           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-    # echo 'hist:keys=skbaddr.hex:vals=len if len > 4096' >> \
-           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-    # echo 'hist:keys=skbaddr.hex:vals=len if len == 256' >> \
-           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-    # echo 'hist:keys=skbaddr.hex:vals=len' >> \
-           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-    # echo 'hist:keys=len:vals=common_preempt_count' >> \
-           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
-  The above set of commands create four triggers differing only in
-  their filters, along with a completely different though fairly
-  nonsensical trigger.  Note that in order to append multiple hist
-  triggers to the same file, you should use the '>>' operator to
-  append them ('>' will also add the new hist trigger, but will remove
-  any existing hist triggers beforehand).
-
-  Displaying the contents of the 'hist' file for the event shows the
-  contents of all five histograms:
-
-    # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
-
-    # event histogram
-    #
-    # trigger info: hist:keys=len:vals=hitcount,common_preempt_count:sort=hitcount:size=2048 [active]
-    #
-
-    { len:        176 } hitcount:          1  common_preempt_count:          0
-    { len:        223 } hitcount:          1  common_preempt_count:          0
-    { len:       4854 } hitcount:          1  common_preempt_count:          0
-    { len:        395 } hitcount:          1  common_preempt_count:          0
-    { len:        177 } hitcount:          1  common_preempt_count:          0
-    { len:        446 } hitcount:          1  common_preempt_count:          0
-    { len:       1601 } hitcount:          1  common_preempt_count:          0
-    .
-    .
-    .
-    { len:       1280 } hitcount:         66  common_preempt_count:          0
-    { len:        116 } hitcount:         81  common_preempt_count:         40
-    { len:        708 } hitcount:        112  common_preempt_count:          0
-    { len:         46 } hitcount:        221  common_preempt_count:          0
-    { len:       1264 } hitcount:        458  common_preempt_count:          0
-
-    Totals:
-        Hits: 1428
-        Entries: 147
-        Dropped: 0
-
-
-    # event histogram
-    #
-    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
-    #
-
-    { skbaddr: ffff8800baee5e00 } hitcount:          1  len:        130
-    { skbaddr: ffff88005f3d5600 } hitcount:          1  len:       1280
-    { skbaddr: ffff88005f3d4900 } hitcount:          1  len:       1280
-    { skbaddr: ffff88009fed6300 } hitcount:          1  len:        115
-    { skbaddr: ffff88009fe0ad00 } hitcount:          1  len:        115
-    { skbaddr: ffff88008cdb1900 } hitcount:          1  len:         46
-    { skbaddr: ffff880064b5ef00 } hitcount:          1  len:        118
-    { skbaddr: ffff880044e3c700 } hitcount:          1  len:         60
-    { skbaddr: ffff880100065900 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d46bd500 } hitcount:          1  len:        116
-    { skbaddr: ffff88005f3d5f00 } hitcount:          1  len:       1280
-    { skbaddr: ffff880100064700 } hitcount:          1  len:        365
-    { skbaddr: ffff8800badb6f00 } hitcount:          1  len:         60
-    .
-    .
-    .
-    { skbaddr: ffff88009fe0be00 } hitcount:         27  len:      24677
-    { skbaddr: ffff88009fe0a400 } hitcount:         27  len:      23052
-    { skbaddr: ffff88009fe0b700 } hitcount:         31  len:      25589
-    { skbaddr: ffff88009fe0b600 } hitcount:         32  len:      27326
-    { skbaddr: ffff88006a462800 } hitcount:         68  len:      71678
-    { skbaddr: ffff88006a463700 } hitcount:         70  len:      72678
-    { skbaddr: ffff88006a462b00 } hitcount:         71  len:      77589
-    { skbaddr: ffff88006a463600 } hitcount:         73  len:      71307
-    { skbaddr: ffff88006a462200 } hitcount:         81  len:      81032
-
-    Totals:
-        Hits: 1451
-        Entries: 318
-        Dropped: 0
-
-
-    # event histogram
-    #
-    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len == 256 [active]
-    #
-
-
-    Totals:
-        Hits: 0
-        Entries: 0
-        Dropped: 0
-
-
-    # event histogram
-    #
-    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len > 4096 [active]
-    #
-
-    { skbaddr: ffff88009fd2c300 } hitcount:          1  len:       7212
-    { skbaddr: ffff8800d2bcce00 } hitcount:          1  len:       7212
-    { skbaddr: ffff8800d2bcd700 } hitcount:          1  len:       7212
-    { skbaddr: ffff8800d2bcda00 } hitcount:          1  len:      21492
-    { skbaddr: ffff8800ae2e2d00 } hitcount:          1  len:       7212
-    { skbaddr: ffff8800d2bcdb00 } hitcount:          1  len:       7212
-    { skbaddr: ffff88006a4df500 } hitcount:          1  len:       4854
-    { skbaddr: ffff88008ce47b00 } hitcount:          1  len:      18636
-    { skbaddr: ffff8800ae2e2200 } hitcount:          1  len:      12924
-    { skbaddr: ffff88005f3e1000 } hitcount:          1  len:       4356
-    { skbaddr: ffff8800d2bcdc00 } hitcount:          2  len:      24420
-    { skbaddr: ffff8800d2bcc200 } hitcount:          2  len:      12996
-
-    Totals:
-        Hits: 14
-        Entries: 12
-        Dropped: 0
-
-
-    # event histogram
-    #
-    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len < 0 [active]
-    #
-
-
-    Totals:
-        Hits: 0
-        Entries: 0
-        Dropped: 0
-
-  Named triggers can be used to have triggers share a common set of
-  histogram data.  This capability is mostly useful for combining the
-  output of events generated by tracepoints contained inside inline
-  functions, but names can be used in a hist trigger on any event.
-  For example, these two triggers when hit will update the same 'len'
-  field in the shared 'foo' histogram data:
-
-    # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
-           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-    # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
-           /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
-  You can see that they're updating common histogram data by reading
-  each event's hist files at the same time:
-
-    # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist;
-      cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
-
-    # event histogram
-    #
-    # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
-    #
-
-    { skbaddr: ffff88000ad53500 } hitcount:          1  len:         46
-    { skbaddr: ffff8800af5a1500 } hitcount:          1  len:         76
-    { skbaddr: ffff8800d62a1900 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d2bccb00 } hitcount:          1  len:        468
-    { skbaddr: ffff8800d3c69900 } hitcount:          1  len:         46
-    { skbaddr: ffff88009ff09100 } hitcount:          1  len:         52
-    { skbaddr: ffff88010f13ab00 } hitcount:          1  len:        168
-    { skbaddr: ffff88006a54f400 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d2bcc500 } hitcount:          1  len:        260
-    { skbaddr: ffff880064505000 } hitcount:          1  len:         46
-    { skbaddr: ffff8800baf24e00 } hitcount:          1  len:         32
-    { skbaddr: ffff88009fe0ad00 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d3edff00 } hitcount:          1  len:         44
-    { skbaddr: ffff88009fe0b400 } hitcount:          1  len:        168
-    { skbaddr: ffff8800a1c55a00 } hitcount:          1  len:         40
-    { skbaddr: ffff8800d2bcd100 } hitcount:          1  len:         40
-    { skbaddr: ffff880064505f00 } hitcount:          1  len:        174
-    { skbaddr: ffff8800a8bff200 } hitcount:          1  len:        160
-    { skbaddr: ffff880044e3cc00 } hitcount:          1  len:         76
-    { skbaddr: ffff8800a8bfe700 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d2bcdc00 } hitcount:          1  len:         32
-    { skbaddr: ffff8800a1f64800 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d2bcde00 } hitcount:          1  len:        988
-    { skbaddr: ffff88006a5dea00 } hitcount:          1  len:         46
-    { skbaddr: ffff88002e37a200 } hitcount:          1  len:         44
-    { skbaddr: ffff8800a1f32c00 } hitcount:          2  len:        676
-    { skbaddr: ffff88000ad52600 } hitcount:          2  len:        107
-    { skbaddr: ffff8800a1f91e00 } hitcount:          2  len:         92
-    { skbaddr: ffff8800af5a0200 } hitcount:          2  len:        142
-    { skbaddr: ffff8800d2bcc600 } hitcount:          2  len:        220
-    { skbaddr: ffff8800ba36f500 } hitcount:          2  len:         92
-    { skbaddr: ffff8800d021f800 } hitcount:          2  len:         92
-    { skbaddr: ffff8800a1f33600 } hitcount:          2  len:        675
-    { skbaddr: ffff8800a8bfff00 } hitcount:          3  len:        138
-    { skbaddr: ffff8800d62a1300 } hitcount:          3  len:        138
-    { skbaddr: ffff88002e37a100 } hitcount:          4  len:        184
-    { skbaddr: ffff880064504400 } hitcount:          4  len:        184
-    { skbaddr: ffff8800a8bfec00 } hitcount:          4  len:        184
-    { skbaddr: ffff88000ad53700 } hitcount:          5  len:        230
-    { skbaddr: ffff8800d2bcdb00 } hitcount:          5  len:        196
-    { skbaddr: ffff8800a1f90000 } hitcount:          6  len:        276
-    { skbaddr: ffff88006a54f900 } hitcount:          6  len:        276
-
-    Totals:
-        Hits: 81
-        Entries: 42
-        Dropped: 0
-    # event histogram
-    #
-    # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
-    #
-
-    { skbaddr: ffff88000ad53500 } hitcount:          1  len:         46
-    { skbaddr: ffff8800af5a1500 } hitcount:          1  len:         76
-    { skbaddr: ffff8800d62a1900 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d2bccb00 } hitcount:          1  len:        468
-    { skbaddr: ffff8800d3c69900 } hitcount:          1  len:         46
-    { skbaddr: ffff88009ff09100 } hitcount:          1  len:         52
-    { skbaddr: ffff88010f13ab00 } hitcount:          1  len:        168
-    { skbaddr: ffff88006a54f400 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d2bcc500 } hitcount:          1  len:        260
-    { skbaddr: ffff880064505000 } hitcount:          1  len:         46
-    { skbaddr: ffff8800baf24e00 } hitcount:          1  len:         32
-    { skbaddr: ffff88009fe0ad00 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d3edff00 } hitcount:          1  len:         44
-    { skbaddr: ffff88009fe0b400 } hitcount:          1  len:        168
-    { skbaddr: ffff8800a1c55a00 } hitcount:          1  len:         40
-    { skbaddr: ffff8800d2bcd100 } hitcount:          1  len:         40
-    { skbaddr: ffff880064505f00 } hitcount:          1  len:        174
-    { skbaddr: ffff8800a8bff200 } hitcount:          1  len:        160
-    { skbaddr: ffff880044e3cc00 } hitcount:          1  len:         76
-    { skbaddr: ffff8800a8bfe700 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d2bcdc00 } hitcount:          1  len:         32
-    { skbaddr: ffff8800a1f64800 } hitcount:          1  len:         46
-    { skbaddr: ffff8800d2bcde00 } hitcount:          1  len:        988
-    { skbaddr: ffff88006a5dea00 } hitcount:          1  len:         46
-    { skbaddr: ffff88002e37a200 } hitcount:          1  len:         44
-    { skbaddr: ffff8800a1f32c00 } hitcount:          2  len:        676
-    { skbaddr: ffff88000ad52600 } hitcount:          2  len:        107
-    { skbaddr: ffff8800a1f91e00 } hitcount:          2  len:         92
-    { skbaddr: ffff8800af5a0200 } hitcount:          2  len:        142
-    { skbaddr: ffff8800d2bcc600 } hitcount:          2  len:        220
-    { skbaddr: ffff8800ba36f500 } hitcount:          2  len:         92
-    { skbaddr: ffff8800d021f800 } hitcount:          2  len:         92
-    { skbaddr: ffff8800a1f33600 } hitcount:          2  len:        675
-    { skbaddr: ffff8800a8bfff00 } hitcount:          3  len:        138
-    { skbaddr: ffff8800d62a1300 } hitcount:          3  len:        138
-    { skbaddr: ffff88002e37a100 } hitcount:          4  len:        184
-    { skbaddr: ffff880064504400 } hitcount:          4  len:        184
-    { skbaddr: ffff8800a8bfec00 } hitcount:          4  len:        184
-    { skbaddr: ffff88000ad53700 } hitcount:          5  len:        230
-    { skbaddr: ffff8800d2bcdb00 } hitcount:          5  len:        196
-    { skbaddr: ffff8800a1f90000 } hitcount:          6  len:        276
-    { skbaddr: ffff88006a54f900 } hitcount:          6  len:        276
-
-    Totals:
-        Hits: 81
-        Entries: 42
-        Dropped: 0
-
-  And here's an example that shows how to combine histogram data from
-  any two events even if they don't share any 'compatible' fields
-  other than 'hitcount' and 'stacktrace'.  These commands create a
-  couple of triggers named 'bar' using those fields:
-
-    # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
-           /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
-    # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
-          /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
-  And displaying the output of either shows some interesting if
-  somewhat confusing output:
-
-    # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
-    # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
-
-    # event histogram
-    #
-    # trigger info: hist:name=bar:keys=stacktrace:vals=hitcount:sort=hitcount:size=2048 [active]
-    #
-
-    { stacktrace:
-             _do_fork+0x18e/0x330
-             kernel_thread+0x29/0x30
-             kthreadd+0x154/0x1b0
-             ret_from_fork+0x3f/0x70
-    } hitcount:          1
-    { stacktrace:
-             netif_rx_internal+0xb2/0xd0
-             netif_rx_ni+0x20/0x70
-             dev_loopback_xmit+0xaa/0xd0
-             ip_mc_output+0x126/0x240
-             ip_local_out_sk+0x31/0x40
-             igmp_send_report+0x1e9/0x230
-             igmp_timer_expire+0xe9/0x120
-             call_timer_fn+0x39/0xf0
-             run_timer_softirq+0x1e1/0x290
-             __do_softirq+0xfd/0x290
-             irq_exit+0x98/0xb0
-             smp_apic_timer_interrupt+0x4a/0x60
-             apic_timer_interrupt+0x6d/0x80
-             cpuidle_enter+0x17/0x20
-             call_cpuidle+0x3b/0x60
-             cpu_startup_entry+0x22d/0x310
-    } hitcount:          1
-    { stacktrace:
-             netif_rx_internal+0xb2/0xd0
-             netif_rx_ni+0x20/0x70
-             dev_loopback_xmit+0xaa/0xd0
-             ip_mc_output+0x17f/0x240
-             ip_local_out_sk+0x31/0x40
-             ip_send_skb+0x1a/0x50
-             udp_send_skb+0x13e/0x270
-             udp_sendmsg+0x2bf/0x980
-             inet_sendmsg+0x67/0xa0
-             sock_sendmsg+0x38/0x50
-             SYSC_sendto+0xef/0x170
-             SyS_sendto+0xe/0x10
-             entry_SYSCALL_64_fastpath+0x12/0x6a
-    } hitcount:          2
-    { stacktrace:
-             netif_rx_internal+0xb2/0xd0
-             netif_rx+0x1c/0x60
-             loopback_xmit+0x6c/0xb0
-             dev_hard_start_xmit+0x219/0x3a0
-             __dev_queue_xmit+0x415/0x4f0
-             dev_queue_xmit_sk+0x13/0x20
-             ip_finish_output2+0x237/0x340
-             ip_finish_output+0x113/0x1d0
-             ip_output+0x66/0xc0
-             ip_local_out_sk+0x31/0x40
-             ip_send_skb+0x1a/0x50
-             udp_send_skb+0x16d/0x270
-             udp_sendmsg+0x2bf/0x980
-             inet_sendmsg+0x67/0xa0
-             sock_sendmsg+0x38/0x50
-             ___sys_sendmsg+0x14e/0x270
-    } hitcount:         76
-    { stacktrace:
-             netif_rx_internal+0xb2/0xd0
-             netif_rx+0x1c/0x60
-             loopback_xmit+0x6c/0xb0
-             dev_hard_start_xmit+0x219/0x3a0
-             __dev_queue_xmit+0x415/0x4f0
-             dev_queue_xmit_sk+0x13/0x20
-             ip_finish_output2+0x237/0x340
-             ip_finish_output+0x113/0x1d0
-             ip_output+0x66/0xc0
-             ip_local_out_sk+0x31/0x40
-             ip_send_skb+0x1a/0x50
-             udp_send_skb+0x16d/0x270
-             udp_sendmsg+0x2bf/0x980
-             inet_sendmsg+0x67/0xa0
-             sock_sendmsg+0x38/0x50
-             ___sys_sendmsg+0x269/0x270
-    } hitcount:         77
-    { stacktrace:
-             netif_rx_internal+0xb2/0xd0
-             netif_rx+0x1c/0x60
-             loopback_xmit+0x6c/0xb0
-             dev_hard_start_xmit+0x219/0x3a0
-             __dev_queue_xmit+0x415/0x4f0
-             dev_queue_xmit_sk+0x13/0x20
-             ip_finish_output2+0x237/0x340
-             ip_finish_output+0x113/0x1d0
-             ip_output+0x66/0xc0
-             ip_local_out_sk+0x31/0x40
-             ip_send_skb+0x1a/0x50
-             udp_send_skb+0x16d/0x270
-             udp_sendmsg+0x2bf/0x980
-             inet_sendmsg+0x67/0xa0
-             sock_sendmsg+0x38/0x50
-             SYSC_sendto+0xef/0x170
-    } hitcount:         88
-    { stacktrace:
-             _do_fork+0x18e/0x330
-             SyS_clone+0x19/0x20
-             entry_SYSCALL_64_fastpath+0x12/0x6a
-    } hitcount:        244
-
-    Totals:
-        Hits: 489
-        Entries: 7
-        Dropped: 0
-
-6.3 Inter-event hist triggers
------------------------------
-
-Inter-event hist triggers are hist triggers that combine values from
-one or more other events and create a histogram using that data.  Data
-from an inter-event histogram can in turn become the source for
-further combined histograms, thus providing a chain of related
-histograms, which is important for some applications.
-
-The most important example of an inter-event quantity that can be used
-in this manner is latency, which is simply a difference in timestamps
-between two events (although trace events don't have an externally
-visible timestamp field, the inter-event hist trigger support adds a
-pseudo-field to all events named '$common_timestamp' which can be used
-as if it were an actual event field).  Although latency is the most
-important inter-event quantity, note that because the support is
-completely general across the trace event subsystem, any event field
-can be used in an inter-event quantity.
-
-An example of a histogram that combines data from other histograms
-into a useful chain would be a 'wakeupswitch latency' histogram that
-combines a 'wakeup latency' histogram and a 'switch latency'
-histogram.
-
-Normally, a hist trigger specification consists of a (possibly
-compound) key along with one or more numeric values, which are
-continually updated sums associated with that key.  A histogram
-specification in this case consists of individual key and value
-specifications that refer to trace event fields associated with a
-single event type.
-
-The inter-event hist trigger extension allows fields from multiple
-events to be referenced and combined into a multi-event histogram
-specification.  In support of this overall goal, a few enabling
-features have been added to the hist trigger support:
-
-  - In order to compute an inter-event quantity, a value from one
-    event needs to saved and then referenced from another event.  This
-    requires the introduction of support for histogram 'variables'.
-
-  - The computation of inter-event quantities and their combination
-    require some minimal amount of support for applying simple
-    expressions to variables (+ and -).
-
-  - A histogram consisting of inter-event quantities isn't logically a
-    histogram on either event (so having the 'hist' file for either
-    event host the histogram output doesn't really make sense).  To
-    address the idea that the histogram is associated with a
-    combination of events, support is added allowing the creation of
-    'synthetic' events that are events derived from other events.
-    These synthetic events are full-fledged events just like any other
-    and can be used as such, as for instance to create the
-    'combination' histograms mentioned previously.
-
-  - A set of 'actions' can be associated with histogram entries -
-    these can be used to generate the previously mentioned synthetic
-    events, but can also be used for other purposes, such as for
-    example saving context when a 'max' latency has been hit.
-
-  - Trace events don't have a 'timestamp' associated with them, but
-    there is an implicit timestamp saved along with an event in the
-    underlying ftrace ring buffer.  This timestamp is now exposed as a
-    a synthetic field named '$common_timestamp' which can be used in
-    histograms as if it were any other event field.  Note that it has
-    a '$' prefixed to it - this is meant to indicate that it isn't an
-    actual field in the trace format but rather is a synthesized value
-    that nonetheless can be used as if it were an actual field.  By
-    default it is in units of nanoseconds; appending '.usecs' to a
-    common_timestamp field changes the units to microseconds.
-
-A note on inter-event timestamps: If $common_timestamp is used in a
-histogram, the trace buffer is automatically switched over to using
-absolute timestamps and the "global" trace clock, in order to avoid
-bogus timestamp differences with other clocks that aren't coherent
-across CPUs.  This can be overridden by specifying one of the other
-trace clocks instead, using the "clock=XXX" hist trigger attribute,
-where XXX is any of the clocks listed in the tracing/trace_clock
-pseudo-file.
-
-These features are decribed in more detail in the following sections.
-
-6.3.1 Histogram Variables
--------------------------
-
-Variables are simply named locations used for saving and retrieving
-values between matching events.  A 'matching' event is defined as an
-event that has a matching key - if a variable is saved for a histogram
-entry corresponding to that key, any subsequent event with a matching
-key can access that variable.
-
-A variable's value is normally available to any subsequent event until
-it is set to something else by a subsequent event.  The one exception
-to that rule is that any variable used in an expression is essentially
-'read-once' - once it's used by an expression in a subsequent event,
-it's reset to its 'unset' state, which means it can't be used again
-unless it's set again.  This ensures not only that an event doesn't
-use an uninitialized variable in a calculation, but that that variable
-is used only once and not for any unrelated subsequent match.
-
-The basic syntax for saving a variable is to simply prefix a unique
-variable name not corresponding to any keyword along with an '=' sign
-to any event field.
-
-Either keys or values can be saved and retrieved in this way.  This
-creates a variable named 'ts0' for a histogram entry with the key
-'next_pid':
-
-  # echo 'hist:keys=next_pid:vals=$ts0:ts0=$common_timestamp ... >> \
-	event/trigger
-
-The ts0 variable can be accessed by any subsequent event having the
-same pid as 'next_pid'.
-
-Variable references are formed by prepending the variable name with
-the '$' sign.  Thus for example, the ts0 variable above would be
-referenced as '$ts0' in expressions.
-
-Because 'vals=' is used, the $common_timestamp variable value above
-will also be summed as a normal histogram value would (though for a
-timestamp it makes little sense).
-
-The below shows that a key value can also be saved in the same way:
-
-  # echo 'hist:timer_pid=common_pid:key=timer_pid ...' >> event/trigger
-
-If a variable isn't a key variable or prefixed with 'vals=', the
-associated event field will be saved in a variable but won't be summed
-as a value:
-
-  # echo 'hist:keys=next_pid:ts1=$common_timestamp ... >> event/trigger
-
-Multiple variables can be assigned at the same time.  The below would
-result in both ts0 and b being created as variables, with both
-common_timestamp and field1 additionally being summed as values:
-
-  # echo 'hist:keys=pid:vals=$ts0,$b:ts0=$common_timestamp,b=field1 ... >> \
-	event/trigger
-
-Note that variable assignments can appear either preceding or
-following their use.  The command below behaves identically to the
-command above:
-
-  # echo 'hist:keys=pid:ts0=$common_timestamp,b=field1:vals=$ts0,$b ... >> \
-	event/trigger
-
-Any number of variables not bound to a 'vals=' prefix can also be
-assigned by simply separating them with colons.  Below is the same
-thing but without the values being summed in the histogram:
-
-  # echo 'hist:keys=pid:ts0=$common_timestamp:b=field1 ... >> event/trigger
-
-Variables set as above can be referenced and used in expressions on
-another event.
-
-For example, here's how a latency can be calculated:
-
-  # echo 'hist:keys=pid,prio:ts0=$common_timestamp ... >> event1/trigger
-  # echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp-$ts0 ... >> event2/trigger
-
-In the first line above, the event's timetamp is saved into the
-variable ts0.  In the next line, ts0 is subtracted from the second
-event's timestamp to produce the latency, which is then assigned into
-yet another variable, 'wakeup_lat'.  The hist trigger below in turn
-makes use of the wakeup_lat variable to compute a combined latency
-using the same key and variable from yet another event:
-
-  # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ... >> event3/trigger
-
-6.3.2 Synthetic Events
-----------------------
-
-Synthetic events are user-defined events generated from hist trigger
-variables or fields associated with one or more other events.  Their
-purpose is to provide a mechanism for displaying data spanning
-multiple events consistent with the existing and already familiar
-usage for normal events.
-
-To define a synthetic event, the user writes a simple specification
-consisting of the name of the new event along with one or more
-variables and their types, which can be any valid field type,
-separated by semicolons, to the tracing/synthetic_events file.
-
-For instance, the following creates a new event named 'wakeup_latency'
-with 3 fields: lat, pid, and prio.  Each of those fields is simply a
-variable reference to a variable on another event:
-
-  # echo 'wakeup_latency \
-          u64 lat; \
-          pid_t pid; \
-	  int prio' >> \
-	  /sys/kernel/debug/tracing/synthetic_events
-
-Reading the tracing/synthetic_events file lists all the currently
-defined synthetic events, in this case the event defined above:
-
-  # cat /sys/kernel/debug/tracing/synthetic_events
-    wakeup_latency u64 lat; pid_t pid; int prio
-
-An existing synthetic event definition can be removed by prepending
-the command that defined it with a '!':
-
-  # echo '!wakeup_latency u64 lat pid_t pid int prio' >> \
-    /sys/kernel/debug/tracing/synthetic_events
-
-At this point, there isn't yet an actual 'wakeup_latency' event
-instantiated in the event subsytem - for this to happen, a 'hist
-trigger action' needs to be instantiated and bound to actual fields
-and variables defined on other events (see Section 6.3.3 below).
-
-Once that is done, an event instance is created, and a histogram can
-be defined using it:
-
-  # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \
-        /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
-
-The new event is created under the tracing/events/synthetic/ directory
-and looks and behaves just like any other event:
-
-  # ls /sys/kernel/debug/tracing/events/synthetic/wakeup_latency
-        enable  filter  format  hist  id  trigger
-
-Like any other event, once a histogram is enabled for the event, the
-output can be displayed by reading the event's 'hist' file.
-
-6.3.3 Hist trigger 'actions'
-----------------------------
-
-A hist trigger 'action' is a function that's executed whenever a
-histogram entry is added or updated.
-
-The default 'action' if no special function is explicity specified is
-as it always has been, to simply update the set of values associated
-with an entry.  Some applications, however, may want to perform
-additional actions at that point, such as generate another event, or
-compare and save a maximum.
-
-The following additional actions are available.  To specify an action
-for a given event, simply specify the action between colons in the
-hist trigger specification.
-
-  - onmatch(matching.event).<synthetic_event_name>(param list)
-
-    The 'onmatch(matching.event).<synthetic_event_name>(params)' hist
-    trigger action is invoked whenever an event matches and the
-    histogram entry would be added or updated.  It causes the named
-    synthetic event to be generated with the values given in the
-    'param list'.  The result is the generation of a synthetic event
-    that consists of the values contained in those variables at the
-    time the invoking event was hit.
-
-    The 'param list' consists of one or more parameters which may be
-    either variables or fields defined on either the 'matching.event'
-    or the target event.  The variables or fields specified in the
-    param list may be either fully-qualified or unqualified.  If a
-    variable is specified as unqualified, it must be unique between
-    the two events.  A field name used as a param can be unqualified
-    if it refers to the target event, but must be fully qualified if
-    it refers to the matching event.  A fully-qualified name is of the
-    form 'system.event_name.$var_name' or 'system.event_name.field'.
-
-    The 'matching.event' specification is simply the fully qualified
-    event name of the event that matches the target event for the
-    onmatch() functionality, in the form 'system.event_name'.
-
-    Finally, the number and type of variables/fields in the 'param
-    list' must match the number and types of the fields in the
-    synthetic event being generated.
-
-    As an example the below defines a simple synthetic event and uses
-    a variable defined on the sched_wakeup_new event as a parameter
-    when invoking the synthetic event.  Here we define the synthetic
-    event:
-
-    # echo 'wakeup_new_test pid_t pid' >> \
-           /sys/kernel/debug/tracing/synthetic_events
-
-    # cat /sys/kernel/debug/tracing/synthetic_events
-          wakeup_new_test pid_t pid
-
-    The following hist trigger both defines the missing testpid
-    variable and specifies an onmatch() action that generates a
-    wakeup_new_test synthetic event whenever a sched_wakeup_new event
-    occurs, which because of the 'if comm == "cyclictest"' filter only
-    happens when the executable is cyclictest:
-
-    # echo 'hist:keys=$testpid:testpid=pid:onmatch(sched.sched_wakeup_new).\
-            wakeup_new_test($testpid) if comm=="cyclictest"' >> \
-            /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger
-
-    Creating and displaying a histogram based on those events is now
-    just a matter of using the fields and new synthetic event in the
-    tracing/events/synthetic directory, as usual:
-
-    # echo 'hist:keys=pid:sort=pid' >> \
-           /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/trigger
-
-    Running 'cyclictest' should cause wakeup_new events to generate
-    wakeup_new_test synthetic events which should result in histogram
-    output in the wakeup_new_test event's hist file:
-
-    # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/hist
-
-    A more typical usage would be to use two events to calculate a
-    latency.  The following example uses a set of hist triggers to
-    produce a 'wakeup_latency' histogram:
-
-    First, we define a 'wakeup_latency' synthetic event:
-
-    # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \
-            /sys/kernel/debug/tracing/synthetic_events
-
-    Next, we specify that whenever we see a sched_waking event for a
-    cyclictest thread, save the timestamp in a 'ts0' variable:
-
-    # echo 'hist:keys=$saved_pid:saved_pid=pid:ts0=$common_timestamp.usecs \
-            if comm=="cyclictest"' >> \
-	    /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
-
-    Then, when the corresponding thread is actually scheduled onto the
-    CPU by a sched_switch event, calculate the latency and use that
-    along with another variable and an event field to generate a
-    wakeup_latency synthetic event:
-
-    # echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp.usecs-$ts0:\
-            onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,\
-	            $saved_pid,next_prio) if next_comm=="cyclictest"' >> \
-	    /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
-
-    We also need to create a histogram on the wakeup_latency synthetic
-    event in order to aggregate the generated synthetic event data:
-
-    # echo 'hist:keys=pid,prio,lat:sort=pid,lat' >> \
-            /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
-
-    Finally, once we've run cyclictest to actually generate some
-    events, we can see the output by looking at the wakeup_latency
-    synthetic event's hist file:
-
-    # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist
-
-  - onmax(var).save(field,..	.)
-
-    The 'onmax(var).save(field,...)' hist trigger action is invoked
-    whenever the value of 'var' associated with a histogram entry
-    exceeds the current maximum contained in that variable.
-
-    The end result is that the trace event fields specified as the
-    onmax.save() params will be saved if 'var' exceeds the current
-    maximum for that hist trigger entry.  This allows context from the
-    event that exhibited the new maximum to be saved for later
-    reference.  When the histogram is displayed, additional fields
-    displaying the saved values will be printed.
-
-    As an example the below defines a couple of hist triggers, one for
-    sched_waking and another for sched_switch, keyed on pid.  Whenever
-    a sched_waking occurs, the timestamp is saved in the entry
-    corresponding to the current pid, and when the scheduler switches
-    back to that pid, the timestamp difference is calculated.  If the
-    resulting latency, stored in wakeup_lat, exceeds the current
-    maximum latency, the values specified in the save() fields are
-    recoreded:
-
-    # echo 'hist:keys=pid:ts0=$common_timestamp.usecs \
-            if comm=="cyclictest"' >> \
-            /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
-
-    # echo 'hist:keys=next_pid:\
-            wakeup_lat=$common_timestamp.usecs-$ts0:\
-            onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) \
-            if next_comm=="cyclictest"' >> \
-            /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
-
-    When the histogram is displayed, the max value and the saved
-    values corresponding to the max are displayed following the rest
-    of the fields:
-
-    # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist
-      { next_pid:       2255 } hitcount:        239
-        common_timestamp-ts0:          0
-        max:         27
-	next_comm: cyclictest
-        prev_pid:          0  prev_prio:        120  prev_comm: swapper/1
-
-      { next_pid:       2256 } hitcount:       2355
-        common_timestamp-ts0: 0
-        max:         49  next_comm: cyclictest
-        prev_pid:          0  prev_prio:        120  prev_comm: swapper/0
-
-      Totals:
-          Hits: 12970
-          Entries: 2
-          Dropped: 0
+  See Documentation/trace/histogram.txt for details and examples.
diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index d4601df6e72e..54213e5c23f6 100644
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -539,6 +539,30 @@ After mounting tracefs you will have access to the control and output files
 
 	See events.txt for more information.
 
+  timestamp_mode:
+
+	Certain tracers may change the timestamp mode used when
+	logging trace events into the event buffer.  Events with
+	different modes can coexist within a buffer but the mode in
+	effect when an event is logged determines which timestamp mode
+	is used for that event.  The default timestamp mode is
+	'delta'.
+
+	Usual timestamp modes for tracing:
+
+	  # cat timestamp_mode
+	  [delta] absolute
+
+	  The timestamp mode with the square brackets around it is the
+	  one in effect.
+
+	  delta: Default timestamp mode - timestamp is a delta against
+	         a per-buffer timestamp.
+
+	  absolute: The timestamp is a full timestamp, not a delta
+                 against some other value.  As such it takes up more
+                 space and is less efficient.
+
   hwlat_detector:
 
 	Directory for the Hardware Latency Detector.
diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt
new file mode 100644
index 000000000000..aa450bbebf1f
--- /dev/null
+++ b/Documentation/trace/histogram.txt
@@ -0,0 +1,1998 @@
+			     Event Histograms
+
+		    Documentation written by Tom Zanussi
+
+1. Introduction
+===============
+
+  Histogram triggers are special event triggers that can be used to
+  aggregate trace event data into histograms.  For information on
+  trace events and event triggers, see Documentation/trace/events.txt.
+
+
+2. Histogram Trigger Command
+============================
+
+  A histogram trigger command is an event trigger command that
+  aggregates event hits into a hash table keyed on one or more trace
+  event format fields (or stacktrace) and a set of running totals
+  derived from one or more trace event format fields and/or event
+  counts (hitcount).
+
+  The format of a hist trigger is as follows:
+
+        hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>]
+          [:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue]
+          [:clear][:name=histname1] [if <filter>]
+
+  When a matching event is hit, an entry is added to a hash table
+  using the key(s) and value(s) named.  Keys and values correspond to
+  fields in the event's format description.  Values must correspond to
+  numeric fields - on an event hit, the value(s) will be added to a
+  sum kept for that field.  The special string 'hitcount' can be used
+  in place of an explicit value field - this is simply a count of
+  event hits.  If 'values' isn't specified, an implicit 'hitcount'
+  value will be automatically created and used as the only value.
+  Keys can be any field, or the special string 'stacktrace', which
+  will use the event's kernel stacktrace as the key.  The keywords
+  'keys' or 'key' can be used to specify keys, and the keywords
+  'values', 'vals', or 'val' can be used to specify values.  Compound
+  keys consisting of up to two fields can be specified by the 'keys'
+  keyword.  Hashing a compound key produces a unique entry in the
+  table for each unique combination of component keys, and can be
+  useful for providing more fine-grained summaries of event data.
+  Additionally, sort keys consisting of up to two fields can be
+  specified by the 'sort' keyword.  If more than one field is
+  specified, the result will be a 'sort within a sort': the first key
+  is taken to be the primary sort key and the second the secondary
+  key.  If a hist trigger is given a name using the 'name' parameter,
+  its histogram data will be shared with other triggers of the same
+  name, and trigger hits will update this common data.  Only triggers
+  with 'compatible' fields can be combined in this way; triggers are
+  'compatible' if the fields named in the trigger share the same
+  number and type of fields and those fields also have the same names.
+  Note that any two events always share the compatible 'hitcount' and
+  'stacktrace' fields and can therefore be combined using those
+  fields, however pointless that may be.
+
+  'hist' triggers add a 'hist' file to each event's subdirectory.
+  Reading the 'hist' file for the event will dump the hash table in
+  its entirety to stdout.  If there are multiple hist triggers
+  attached to an event, there will be a table for each trigger in the
+  output.  The table displayed for a named trigger will be the same as
+  any other instance having the same name. Each printed hash table
+  entry is a simple list of the keys and values comprising the entry;
+  keys are printed first and are delineated by curly braces, and are
+  followed by the set of value fields for the entry.  By default,
+  numeric fields are displayed as base-10 integers.  This can be
+  modified by appending any of the following modifiers to the field
+  name:
+
+        .hex        display a number as a hex value
+	.sym        display an address as a symbol
+	.sym-offset display an address as a symbol and offset
+	.syscall    display a syscall id as a system call name
+	.execname   display a common_pid as a program name
+	.log2       display log2 value rather than raw number
+	.usecs      display a $common_timestamp in microseconds
+
+  Note that in general the semantics of a given field aren't
+  interpreted when applying a modifier to it, but there are some
+  restrictions to be aware of in this regard:
+
+    - only the 'hex' modifier can be used for values (because values
+      are essentially sums, and the other modifiers don't make sense
+      in that context).
+    - the 'execname' modifier can only be used on a 'common_pid'.  The
+      reason for this is that the execname is simply the 'comm' value
+      saved for the 'current' process when an event was triggered,
+      which is the same as the common_pid value saved by the event
+      tracing code.  Trying to apply that comm value to other pid
+      values wouldn't be correct, and typically events that care save
+      pid-specific comm fields in the event itself.
+
+  A typical usage scenario would be the following to enable a hist
+  trigger, read its current contents, and then turn it off:
+
+  # echo 'hist:keys=skbaddr.hex:vals=len' > \
+    /sys/kernel/debug/tracing/events/net/netif_rx/trigger
+
+  # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
+
+  # echo '!hist:keys=skbaddr.hex:vals=len' > \
+    /sys/kernel/debug/tracing/events/net/netif_rx/trigger
+
+  The trigger file itself can be read to show the details of the
+  currently attached hist trigger.  This information is also displayed
+  at the top of the 'hist' file when read.
+
+  By default, the size of the hash table is 2048 entries.  The 'size'
+  parameter can be used to specify more or fewer than that.  The units
+  are in terms of hashtable entries - if a run uses more entries than
+  specified, the results will show the number of 'drops', the number
+  of hits that were ignored.  The size should be a power of 2 between
+  128 and 131072 (any non- power-of-2 number specified will be rounded
+  up).
+
+  The 'sort' parameter can be used to specify a value field to sort
+  on.  The default if unspecified is 'hitcount' and the default sort
+  order is 'ascending'.  To sort in the opposite direction, append
+  .descending' to the sort key.
+
+  The 'pause' parameter can be used to pause an existing hist trigger
+  or to start a hist trigger but not log any events until told to do
+  so.  'continue' or 'cont' can be used to start or restart a paused
+  hist trigger.
+
+  The 'clear' parameter will clear the contents of a running hist
+  trigger and leave its current paused/active state.
+
+  Note that the 'pause', 'cont', and 'clear' parameters should be
+  applied using 'append' shell operator ('>>') if applied to an
+  existing trigger, rather than via the '>' operator, which will cause
+  the trigger to be removed through truncation.
+
+- enable_hist/disable_hist
+
+  The enable_hist and disable_hist triggers can be used to have one
+  event conditionally start and stop another event's already-attached
+  hist trigger.  Any number of enable_hist and disable_hist triggers
+  can be attached to a given event, allowing that event to kick off
+  and stop aggregations on a host of other events.
+
+  The format is very similar to the enable/disable_event triggers:
+
+      enable_hist:<system>:<event>[:count]
+      disable_hist:<system>:<event>[:count]
+
+  Instead of enabling or disabling the tracing of the target event
+  into the trace buffer as the enable/disable_event triggers do, the
+  enable/disable_hist triggers enable or disable the aggregation of
+  the target event into a hash table.
+
+  A typical usage scenario for the enable_hist/disable_hist triggers
+  would be to first set up a paused hist trigger on some event,
+  followed by an enable_hist/disable_hist pair that turns the hist
+  aggregation on and off when conditions of interest are hit:
+
+  # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \
+    /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+  # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
+    /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+
+  # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
+    /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+
+  The above sets up an initially paused hist trigger which is unpaused
+  and starts aggregating events when a given program is executed, and
+  which stops aggregating when the process exits and the hist trigger
+  is paused again.
+
+  The examples below provide a more concrete illustration of the
+  concepts and typical usage patterns discussed above.
+
+  'special' event fields
+  ------------------------
+
+  There are a number of 'special event fields' available for use as
+  keys or values in a hist trigger.  These look like and behave as if
+  they were actual event fields, but aren't really part of the event's
+  field definition or format file.  They are however available for any
+  event, and can be used anywhere an actual event field could be.
+  'Special' field names are always prefixed with a '$' character to
+  indicate that they're not normal fields (with the exception of
+  'cpu', for compatibility with existing filter usage):
+
+    $common_timestamp      u64 - timestamp (from ring buffer) associated
+                                 with the event, in nanoseconds.  May be
+				 modified by .usecs to have timestamps
+				 interpreted as microseconds.
+    cpu                    int - the cpu on which the event occurred.
+
+  Extended error information
+  --------------------------
+
+  For some error conditions encountered when invoking a hist trigger
+  command, extended error information is available via the
+  corresponding event's 'hist' file.  Reading the hist file after an
+  error will display more detailed information about what went wrong,
+  if information is available.  This extended error information will
+  be available until the next hist trigger command for that event.
+
+  If available for a given error condition, the extended error
+  information and usage takes the following form:
+
+    # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
+    echo: write error: Invalid argument
+
+    # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/hist
+    ERROR: Couldn't yyy: zzz
+      Last command: xxx
+
+6.2 'hist' trigger examples
+---------------------------
+
+  The first set of examples creates aggregations using the kmalloc
+  event.  The fields that can be used for the hist trigger are listed
+  in the kmalloc event's format file:
+
+    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/format
+    name: kmalloc
+    ID: 374
+    format:
+	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
+	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
+	field:unsigned char common_preempt_count;		offset:3;	size:1;	signed:0;
+	field:int common_pid;					offset:4;	size:4;	signed:1;
+
+	field:unsigned long call_site;				offset:8;	size:8;	signed:0;
+	field:const void * ptr;					offset:16;	size:8;	signed:0;
+	field:size_t bytes_req;					offset:24;	size:8;	signed:0;
+	field:size_t bytes_alloc;				offset:32;	size:8;	signed:0;
+	field:gfp_t gfp_flags;					offset:40;	size:4;	signed:0;
+
+  We'll start by creating a hist trigger that generates a simple table
+  that lists the total number of bytes requested for each function in
+  the kernel that made one or more calls to kmalloc:
+
+    # echo 'hist:key=call_site:val=bytes_req' > \
+            /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+  This tells the tracing system to create a 'hist' trigger using the
+  call_site field of the kmalloc event as the key for the table, which
+  just means that each unique call_site address will have an entry
+  created for it in the table.  The 'val=bytes_req' parameter tells
+  the hist trigger that for each unique entry (call_site) in the
+  table, it should keep a running total of the number of bytes
+  requested by that call_site.
+
+  We'll let it run for awhile and then dump the contents of the 'hist'
+  file in the kmalloc event's subdirectory (for readability, a number
+  of entries have been omitted):
+
+    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+    # trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+    { call_site: 18446744072106379007 } hitcount:          1  bytes_req:        176
+    { call_site: 18446744071579557049 } hitcount:          1  bytes_req:       1024
+    { call_site: 18446744071580608289 } hitcount:          1  bytes_req:      16384
+    { call_site: 18446744071581827654 } hitcount:          1  bytes_req:         24
+    { call_site: 18446744071580700980 } hitcount:          1  bytes_req:          8
+    { call_site: 18446744071579359876 } hitcount:          1  bytes_req:        152
+    { call_site: 18446744071580795365 } hitcount:          3  bytes_req:        144
+    { call_site: 18446744071581303129 } hitcount:          3  bytes_req:        144
+    { call_site: 18446744071580713234 } hitcount:          4  bytes_req:       2560
+    { call_site: 18446744071580933750 } hitcount:          4  bytes_req:        736
+    .
+    .
+    .
+    { call_site: 18446744072106047046 } hitcount:         69  bytes_req:       5576
+    { call_site: 18446744071582116407 } hitcount:         73  bytes_req:       2336
+    { call_site: 18446744072106054684 } hitcount:        136  bytes_req:     140504
+    { call_site: 18446744072106224230 } hitcount:        136  bytes_req:      19584
+    { call_site: 18446744072106078074 } hitcount:        153  bytes_req:       2448
+    { call_site: 18446744072106062406 } hitcount:        153  bytes_req:      36720
+    { call_site: 18446744071582507929 } hitcount:        153  bytes_req:      37088
+    { call_site: 18446744072102520590 } hitcount:        273  bytes_req:      10920
+    { call_site: 18446744071582143559 } hitcount:        358  bytes_req:        716
+    { call_site: 18446744072106465852 } hitcount:        417  bytes_req:      56712
+    { call_site: 18446744072102523378 } hitcount:        485  bytes_req:      27160
+    { call_site: 18446744072099568646 } hitcount:       1676  bytes_req:      33520
+
+    Totals:
+        Hits: 4610
+        Entries: 45
+        Dropped: 0
+
+  The output displays a line for each entry, beginning with the key
+  specified in the trigger, followed by the value(s) also specified in
+  the trigger.  At the beginning of the output is a line that displays
+  the trigger info, which can also be displayed by reading the
+  'trigger' file:
+
+    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+    hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+  At the end of the output are a few lines that display the overall
+  totals for the run.  The 'Hits' field shows the total number of
+  times the event trigger was hit, the 'Entries' field shows the total
+  number of used entries in the hash table, and the 'Dropped' field
+  shows the number of hits that were dropped because the number of
+  used entries for the run exceeded the maximum number of entries
+  allowed for the table (normally 0, but if not a hint that you may
+  want to increase the size of the table using the 'size' parameter).
+
+  Notice in the above output that there's an extra field, 'hitcount',
+  which wasn't specified in the trigger.  Also notice that in the
+  trigger info output, there's a parameter, 'sort=hitcount', which
+  wasn't specified in the trigger either.  The reason for that is that
+  every trigger implicitly keeps a count of the total number of hits
+  attributed to a given entry, called the 'hitcount'.  That hitcount
+  information is explicitly displayed in the output, and in the
+  absence of a user-specified sort parameter, is used as the default
+  sort field.
+
+  The value 'hitcount' can be used in place of an explicit value in
+  the 'values' parameter if you don't really need to have any
+  particular field summed and are mainly interested in hit
+  frequencies.
+
+  To turn the hist trigger off, simply call up the trigger in the
+  command history and re-execute it with a '!' prepended:
+
+    # echo '!hist:key=call_site:val=bytes_req' > \
+           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+  Finally, notice that the call_site as displayed in the output above
+  isn't really very useful.  It's an address, but normally addresses
+  are displayed in hex.  To have a numeric field displayed as a hex
+  value, simply append '.hex' to the field name in the trigger:
+
+    # echo 'hist:key=call_site.hex:val=bytes_req' > \
+           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+    # trigger info: hist:keys=call_site.hex:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+    { call_site: ffffffffa026b291 } hitcount:          1  bytes_req:        433
+    { call_site: ffffffffa07186ff } hitcount:          1  bytes_req:        176
+    { call_site: ffffffff811ae721 } hitcount:          1  bytes_req:      16384
+    { call_site: ffffffff811c5134 } hitcount:          1  bytes_req:          8
+    { call_site: ffffffffa04a9ebb } hitcount:          1  bytes_req:        511
+    { call_site: ffffffff8122e0a6 } hitcount:          1  bytes_req:         12
+    { call_site: ffffffff8107da84 } hitcount:          1  bytes_req:        152
+    { call_site: ffffffff812d8246 } hitcount:          1  bytes_req:         24
+    { call_site: ffffffff811dc1e5 } hitcount:          3  bytes_req:        144
+    { call_site: ffffffffa02515e8 } hitcount:          3  bytes_req:        648
+    { call_site: ffffffff81258159 } hitcount:          3  bytes_req:        144
+    { call_site: ffffffff811c80f4 } hitcount:          4  bytes_req:        544
+    .
+    .
+    .
+    { call_site: ffffffffa06c7646 } hitcount:        106  bytes_req:       8024
+    { call_site: ffffffffa06cb246 } hitcount:        132  bytes_req:      31680
+    { call_site: ffffffffa06cef7a } hitcount:        132  bytes_req:       2112
+    { call_site: ffffffff8137e399 } hitcount:        132  bytes_req:      23232
+    { call_site: ffffffffa06c941c } hitcount:        185  bytes_req:     171360
+    { call_site: ffffffffa06f2a66 } hitcount:        185  bytes_req:      26640
+    { call_site: ffffffffa036a70e } hitcount:        265  bytes_req:      10600
+    { call_site: ffffffff81325447 } hitcount:        292  bytes_req:        584
+    { call_site: ffffffffa072da3c } hitcount:        446  bytes_req:      60656
+    { call_site: ffffffffa036b1f2 } hitcount:        526  bytes_req:      29456
+    { call_site: ffffffffa0099c06 } hitcount:       1780  bytes_req:      35600
+
+    Totals:
+        Hits: 4775
+        Entries: 46
+        Dropped: 0
+
+  Even that's only marginally more useful - while hex values do look
+  more like addresses, what users are typically more interested in
+  when looking at text addresses are the corresponding symbols
+  instead.  To have an address displayed as symbolic value instead,
+  simply append '.sym' or '.sym-offset' to the field name in the
+  trigger:
+
+    # echo 'hist:key=call_site.sym:val=bytes_req' > \
+           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+    # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+    { call_site: [ffffffff810adcb9] syslog_print_all                              } hitcount:          1  bytes_req:       1024
+    { call_site: [ffffffff8154bc62] usb_control_msg                               } hitcount:          1  bytes_req:          8
+    { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid]                      } hitcount:          1  bytes_req:          7
+    { call_site: [ffffffff8154acbe] usb_alloc_urb                                 } hitcount:          1  bytes_req:        192
+    { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid]                     } hitcount:          1  bytes_req:          7
+    { call_site: [ffffffff811e3a25] __seq_open_private                            } hitcount:          1  bytes_req:         40
+    { call_site: [ffffffff8109524a] alloc_fair_sched_group                        } hitcount:          2  bytes_req:        128
+    { call_site: [ffffffff811febd5] fsnotify_alloc_group                          } hitcount:          2  bytes_req:        528
+    { call_site: [ffffffff81440f58] __tty_buffer_request_room                     } hitcount:          2  bytes_req:       2624
+    { call_site: [ffffffff81200ba6] inotify_new_group                             } hitcount:          2  bytes_req:         96
+    { call_site: [ffffffffa05e19af] ieee80211_start_tx_ba_session [mac80211]      } hitcount:          2  bytes_req:        464
+    { call_site: [ffffffff81672406] tcp_get_metrics                               } hitcount:          2  bytes_req:        304
+    { call_site: [ffffffff81097ec2] alloc_rt_sched_group                          } hitcount:          2  bytes_req:        128
+    { call_site: [ffffffff81089b05] sched_create_group                            } hitcount:          2  bytes_req:       1424
+    .
+    .
+    .
+    { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915]                   } hitcount:       1185  bytes_req:     123240
+    { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm]                } hitcount:       1185  bytes_req:     104280
+    { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915]            } hitcount:       1402  bytes_req:     190672
+    { call_site: [ffffffff812891ca] ext4_find_extent                              } hitcount:       1518  bytes_req:     146208
+    { call_site: [ffffffffa029070e] drm_vma_node_allow [drm]                      } hitcount:       1746  bytes_req:      69840
+    { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915]         } hitcount:       2021  bytes_req:     792312
+    { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm]                   } hitcount:       2592  bytes_req:     145152
+    { call_site: [ffffffffa0489a66] intel_ring_begin [i915]                       } hitcount:       2629  bytes_req:     378576
+    { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915]                   } hitcount:       2629  bytes_req:    3783248
+    { call_site: [ffffffff81325607] apparmor_file_alloc_security                  } hitcount:       5192  bytes_req:      10384
+    { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid]                    } hitcount:       5529  bytes_req:     110584
+    { call_site: [ffffffff8131ebf7] aa_alloc_task_context                         } hitcount:      21943  bytes_req:     702176
+    { call_site: [ffffffff8125847d] ext4_htree_store_dirent                       } hitcount:      55759  bytes_req:    5074265
+
+    Totals:
+        Hits: 109928
+        Entries: 71
+        Dropped: 0
+
+  Because the default sort key above is 'hitcount', the above shows a
+  the list of call_sites by increasing hitcount, so that at the bottom
+  we see the functions that made the most kmalloc calls during the
+  run.  If instead we we wanted to see the top kmalloc callers in
+  terms of the number of bytes requested rather than the number of
+  calls, and we wanted the top caller to appear at the top, we can use
+  the 'sort' parameter, along with the 'descending' modifier:
+
+    # echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \
+           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+    # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
+
+    { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915]                   } hitcount:       2186  bytes_req:    3397464
+    { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915]         } hitcount:       1790  bytes_req:     712176
+    { call_site: [ffffffff8125847d] ext4_htree_store_dirent                       } hitcount:       8132  bytes_req:     513135
+    { call_site: [ffffffff811e2a1b] seq_buf_alloc                                 } hitcount:        106  bytes_req:     440128
+    { call_site: [ffffffffa0489a66] intel_ring_begin [i915]                       } hitcount:       2186  bytes_req:     314784
+    { call_site: [ffffffff812891ca] ext4_find_extent                              } hitcount:       2174  bytes_req:     208992
+    { call_site: [ffffffff811ae8e1] __kmalloc                                     } hitcount:          8  bytes_req:     131072
+    { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915]            } hitcount:        859  bytes_req:     116824
+    { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm]                   } hitcount:       1834  bytes_req:     102704
+    { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915]                   } hitcount:        972  bytes_req:     101088
+    { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm]                } hitcount:        972  bytes_req:      85536
+    { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid]                    } hitcount:       3333  bytes_req:      66664
+    { call_site: [ffffffff8137e559] sg_kmalloc                                    } hitcount:        209  bytes_req:      61632
+    .
+    .
+    .
+    { call_site: [ffffffff81095225] alloc_fair_sched_group                        } hitcount:          2  bytes_req:        128
+    { call_site: [ffffffff81097ec2] alloc_rt_sched_group                          } hitcount:          2  bytes_req:        128
+    { call_site: [ffffffff812d8406] copy_semundo                                  } hitcount:          2  bytes_req:         48
+    { call_site: [ffffffff81200ba6] inotify_new_group                             } hitcount:          1  bytes_req:         48
+    { call_site: [ffffffffa027121a] drm_getmagic [drm]                            } hitcount:          1  bytes_req:         48
+    { call_site: [ffffffff811e3a25] __seq_open_private                            } hitcount:          1  bytes_req:         40
+    { call_site: [ffffffff811c52f4] bprm_change_interp                            } hitcount:          2  bytes_req:         16
+    { call_site: [ffffffff8154bc62] usb_control_msg                               } hitcount:          1  bytes_req:          8
+    { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid]                     } hitcount:          1  bytes_req:          7
+    { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid]                      } hitcount:          1  bytes_req:          7
+
+    Totals:
+        Hits: 32133
+        Entries: 81
+        Dropped: 0
+
+  To display the offset and size information in addition to the symbol
+  name, just use 'sym-offset' instead:
+
+    # echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \
+           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+    # trigger info: hist:keys=call_site.sym-offset:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
+
+    { call_site: [ffffffffa046041c] i915_gem_execbuffer2+0x6c/0x2c0 [i915]                  } hitcount:       4569  bytes_req:    3163720
+    { call_site: [ffffffffa0489a66] intel_ring_begin+0xc6/0x1f0 [i915]                      } hitcount:       4569  bytes_req:     657936
+    { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23+0x694/0x1020 [i915]      } hitcount:       1519  bytes_req:     472936
+    { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23+0x516/0x1020 [i915]      } hitcount:       3050  bytes_req:     211832
+    { call_site: [ffffffff811e2a1b] seq_buf_alloc+0x1b/0x50                                 } hitcount:         34  bytes_req:     148384
+    { call_site: [ffffffffa04a580c] intel_crtc_page_flip+0xbc/0x870 [i915]                  } hitcount:       1385  bytes_req:     144040
+    { call_site: [ffffffff811ae8e1] __kmalloc+0x191/0x1b0                                   } hitcount:          8  bytes_req:     131072
+    { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl+0x282/0x360 [drm]              } hitcount:       1385  bytes_req:     121880
+    { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc+0x32/0x100 [drm]                  } hitcount:       1848  bytes_req:     103488
+    { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state+0x2c/0xa0 [i915]            } hitcount:        461  bytes_req:      62696
+    { call_site: [ffffffffa029070e] drm_vma_node_allow+0x2e/0xd0 [drm]                      } hitcount:       1541  bytes_req:      61640
+    { call_site: [ffffffff815f8d7b] sk_prot_alloc+0xcb/0x1b0                                } hitcount:         57  bytes_req:      57456
+    .
+    .
+    .
+    { call_site: [ffffffff8109524a] alloc_fair_sched_group+0x5a/0x1a0                       } hitcount:          2  bytes_req:        128
+    { call_site: [ffffffffa027b921] drm_vm_open_locked+0x31/0xa0 [drm]                      } hitcount:          3  bytes_req:         96
+    { call_site: [ffffffff8122e266] proc_self_follow_link+0x76/0xb0                         } hitcount:          8  bytes_req:         96
+    { call_site: [ffffffff81213e80] load_elf_binary+0x240/0x1650                            } hitcount:          3  bytes_req:         84
+    { call_site: [ffffffff8154bc62] usb_control_msg+0x42/0x110                              } hitcount:          1  bytes_req:          8
+    { call_site: [ffffffffa00bf6fe] hidraw_send_report+0x7e/0x1a0 [hid]                     } hitcount:          1  bytes_req:          7
+    { call_site: [ffffffffa00bf1ca] hidraw_report_event+0x8a/0x120 [hid]                    } hitcount:          1  bytes_req:          7
+
+    Totals:
+        Hits: 26098
+        Entries: 64
+        Dropped: 0
+
+  We can also add multiple fields to the 'values' parameter.  For
+  example, we might want to see the total number of bytes allocated
+  alongside bytes requested, and display the result sorted by bytes
+  allocated in a descending order:
+
+    # echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \
+           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+    # trigger info: hist:keys=call_site.sym:vals=bytes_req,bytes_alloc:sort=bytes_alloc.descending:size=2048 [active]
+
+    { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915]                   } hitcount:       7403  bytes_req:    4084360  bytes_alloc:    5958016
+    { call_site: [ffffffff811e2a1b] seq_buf_alloc                                 } hitcount:        541  bytes_req:    2213968  bytes_alloc:    2228224
+    { call_site: [ffffffffa0489a66] intel_ring_begin [i915]                       } hitcount:       7404  bytes_req:    1066176  bytes_alloc:    1421568
+    { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915]         } hitcount:       1565  bytes_req:     557368  bytes_alloc:    1037760
+    { call_site: [ffffffff8125847d] ext4_htree_store_dirent                       } hitcount:       9557  bytes_req:     595778  bytes_alloc:     695744
+    { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23 [i915]         } hitcount:       5839  bytes_req:     430680  bytes_alloc:     470400
+    { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915]            } hitcount:       2388  bytes_req:     324768  bytes_alloc:     458496
+    { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm]                   } hitcount:       3911  bytes_req:     219016  bytes_alloc:     250304
+    { call_site: [ffffffff815f8d7b] sk_prot_alloc                                 } hitcount:        235  bytes_req:     236880  bytes_alloc:     240640
+    { call_site: [ffffffff8137e559] sg_kmalloc                                    } hitcount:        557  bytes_req:     169024  bytes_alloc:     221760
+    { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid]                    } hitcount:       9378  bytes_req:     187548  bytes_alloc:     206312
+    { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915]                   } hitcount:       1519  bytes_req:     157976  bytes_alloc:     194432
+    .
+    .
+    .
+    { call_site: [ffffffff8109bd3b] sched_autogroup_create_attach                 } hitcount:          2  bytes_req:        144  bytes_alloc:        192
+    { call_site: [ffffffff81097ee8] alloc_rt_sched_group                          } hitcount:          2  bytes_req:        128  bytes_alloc:        128
+    { call_site: [ffffffff8109524a] alloc_fair_sched_group                        } hitcount:          2  bytes_req:        128  bytes_alloc:        128
+    { call_site: [ffffffff81095225] alloc_fair_sched_group                        } hitcount:          2  bytes_req:        128  bytes_alloc:        128
+    { call_site: [ffffffff81097ec2] alloc_rt_sched_group                          } hitcount:          2  bytes_req:        128  bytes_alloc:        128
+    { call_site: [ffffffff81213e80] load_elf_binary                               } hitcount:          3  bytes_req:         84  bytes_alloc:         96
+    { call_site: [ffffffff81079a2e] kthread_create_on_node                        } hitcount:          1  bytes_req:         56  bytes_alloc:         64
+    { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid]                      } hitcount:          1  bytes_req:          7  bytes_alloc:          8
+    { call_site: [ffffffff8154bc62] usb_control_msg                               } hitcount:          1  bytes_req:          8  bytes_alloc:          8
+    { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid]                     } hitcount:          1  bytes_req:          7  bytes_alloc:          8
+
+    Totals:
+        Hits: 66598
+        Entries: 65
+        Dropped: 0
+
+  Finally, to finish off our kmalloc example, instead of simply having
+  the hist trigger display symbolic call_sites, we can have the hist
+  trigger additionally display the complete set of kernel stack traces
+  that led to each call_site.  To do that, we simply use the special
+  value 'stacktrace' for the key parameter:
+
+    # echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \
+           /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+  The above trigger will use the kernel stack trace in effect when an
+  event is triggered as the key for the hash table.  This allows the
+  enumeration of every kernel callpath that led up to a particular
+  event, along with a running total of any of the event fields for
+  that event.  Here we tally bytes requested and bytes allocated for
+  every callpath in the system that led up to a kmalloc (in this case
+  every callpath to a kmalloc for a kernel compile):
+
+    # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+    # trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active]
+
+    { stacktrace:
+         __kmalloc_track_caller+0x10b/0x1a0
+         kmemdup+0x20/0x50
+         hidraw_report_event+0x8a/0x120 [hid]
+         hid_report_raw_event+0x3ea/0x440 [hid]
+         hid_input_report+0x112/0x190 [hid]
+         hid_irq_in+0xc2/0x260 [usbhid]
+         __usb_hcd_giveback_urb+0x72/0x120
+         usb_giveback_urb_bh+0x9e/0xe0
+         tasklet_hi_action+0xf8/0x100
+         __do_softirq+0x114/0x2c0
+         irq_exit+0xa5/0xb0
+         do_IRQ+0x5a/0xf0
+         ret_from_intr+0x0/0x30
+         cpuidle_enter+0x17/0x20
+         cpu_startup_entry+0x315/0x3e0
+         rest_init+0x7c/0x80
+    } hitcount:          3  bytes_req:         21  bytes_alloc:         24
+    { stacktrace:
+         __kmalloc_track_caller+0x10b/0x1a0
+         kmemdup+0x20/0x50
+         hidraw_report_event+0x8a/0x120 [hid]
+         hid_report_raw_event+0x3ea/0x440 [hid]
+         hid_input_report+0x112/0x190 [hid]
+         hid_irq_in+0xc2/0x260 [usbhid]
+         __usb_hcd_giveback_urb+0x72/0x120
+         usb_giveback_urb_bh+0x9e/0xe0
+         tasklet_hi_action+0xf8/0x100
+         __do_softirq+0x114/0x2c0
+         irq_exit+0xa5/0xb0
+         do_IRQ+0x5a/0xf0
+         ret_from_intr+0x0/0x30
+    } hitcount:          3  bytes_req:         21  bytes_alloc:         24
+    { stacktrace:
+         kmem_cache_alloc_trace+0xeb/0x150
+         aa_alloc_task_context+0x27/0x40
+         apparmor_cred_prepare+0x1f/0x50
+         security_prepare_creds+0x16/0x20
+         prepare_creds+0xdf/0x1a0
+         SyS_capset+0xb5/0x200
+         system_call_fastpath+0x12/0x6a
+    } hitcount:          1  bytes_req:         32  bytes_alloc:         32
+    .
+    .
+    .
+    { stacktrace:
+         __kmalloc+0x11b/0x1b0
+         i915_gem_execbuffer2+0x6c/0x2c0 [i915]
+         drm_ioctl+0x349/0x670 [drm]
+         do_vfs_ioctl+0x2f0/0x4f0
+         SyS_ioctl+0x81/0xa0
+         system_call_fastpath+0x12/0x6a
+    } hitcount:      17726  bytes_req:   13944120  bytes_alloc:   19593808
+    { stacktrace:
+         __kmalloc+0x11b/0x1b0
+         load_elf_phdrs+0x76/0xa0
+         load_elf_binary+0x102/0x1650
+         search_binary_handler+0x97/0x1d0
+         do_execveat_common.isra.34+0x551/0x6e0
+         SyS_execve+0x3a/0x50
+         return_from_execve+0x0/0x23
+    } hitcount:      33348  bytes_req:   17152128  bytes_alloc:   20226048
+    { stacktrace:
+         kmem_cache_alloc_trace+0xeb/0x150
+         apparmor_file_alloc_security+0x27/0x40
+         security_file_alloc+0x16/0x20
+         get_empty_filp+0x93/0x1c0
+         path_openat+0x31/0x5f0
+         do_filp_open+0x3a/0x90
+         do_sys_open+0x128/0x220
+         SyS_open+0x1e/0x20
+         system_call_fastpath+0x12/0x6a
+    } hitcount:    4766422  bytes_req:    9532844  bytes_alloc:   38131376
+    { stacktrace:
+         __kmalloc+0x11b/0x1b0
+         seq_buf_alloc+0x1b/0x50
+         seq_read+0x2cc/0x370
+         proc_reg_read+0x3d/0x80
+         __vfs_read+0x28/0xe0
+         vfs_read+0x86/0x140
+         SyS_read+0x46/0xb0
+         system_call_fastpath+0x12/0x6a
+    } hitcount:      19133  bytes_req:   78368768  bytes_alloc:   78368768
+
+    Totals:
+        Hits: 6085872
+        Entries: 253
+        Dropped: 0
+
+  If you key a hist trigger on common_pid, in order for example to
+  gather and display sorted totals for each process, you can use the
+  special .execname modifier to display the executable names for the
+  processes in the table rather than raw pids.  The example below
+  keeps a per-process sum of total bytes read:
+
+    # echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \
+           /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
+
+    # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/hist
+    # trigger info: hist:keys=common_pid.execname:vals=count:sort=count.descending:size=2048 [active]
+
+    { common_pid: gnome-terminal  [      3196] } hitcount:        280  count:    1093512
+    { common_pid: Xorg            [      1309] } hitcount:        525  count:     256640
+    { common_pid: compiz          [      2889] } hitcount:         59  count:     254400
+    { common_pid: bash            [      8710] } hitcount:          3  count:      66369
+    { common_pid: dbus-daemon-lau [      8703] } hitcount:         49  count:      47739
+    { common_pid: irqbalance      [      1252] } hitcount:         27  count:      27648
+    { common_pid: 01ifupdown      [      8705] } hitcount:          3  count:      17216
+    { common_pid: dbus-daemon     [       772] } hitcount:         10  count:      12396
+    { common_pid: Socket Thread   [      8342] } hitcount:         11  count:      11264
+    { common_pid: nm-dhcp-client. [      8701] } hitcount:          6  count:       7424
+    { common_pid: gmain           [      1315] } hitcount:         18  count:       6336
+    .
+    .
+    .
+    { common_pid: postgres        [      1892] } hitcount:          2  count:         32
+    { common_pid: postgres        [      1891] } hitcount:          2  count:         32
+    { common_pid: gmain           [      8704] } hitcount:          2  count:         32
+    { common_pid: upstart-dbus-br [      2740] } hitcount:         21  count:         21
+    { common_pid: nm-dispatcher.a [      8696] } hitcount:          1  count:         16
+    { common_pid: indicator-datet [      2904] } hitcount:          1  count:         16
+    { common_pid: gdbus           [      2998] } hitcount:          1  count:         16
+    { common_pid: rtkit-daemon    [      2052] } hitcount:          1  count:          8
+    { common_pid: init            [         1] } hitcount:          2  count:          2
+
+    Totals:
+        Hits: 2116
+        Entries: 51
+        Dropped: 0
+
+  Similarly, if you key a hist trigger on syscall id, for example to
+  gather and display a list of systemwide syscall hits, you can use
+  the special .syscall modifier to display the syscall names rather
+  than raw ids.  The example below keeps a running total of syscall
+  counts for the system during the run:
+
+    # echo 'hist:key=id.syscall:val=hitcount' > \
+           /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
+
+    # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
+    # trigger info: hist:keys=id.syscall:vals=hitcount:sort=hitcount:size=2048 [active]
+
+    { id: sys_fsync                     [ 74] } hitcount:          1
+    { id: sys_newuname                  [ 63] } hitcount:          1
+    { id: sys_prctl                     [157] } hitcount:          1
+    { id: sys_statfs                    [137] } hitcount:          1
+    { id: sys_symlink                   [ 88] } hitcount:          1
+    { id: sys_sendmmsg                  [307] } hitcount:          1
+    { id: sys_semctl                    [ 66] } hitcount:          1
+    { id: sys_readlink                  [ 89] } hitcount:          3
+    { id: sys_bind                      [ 49] } hitcount:          3
+    { id: sys_getsockname               [ 51] } hitcount:          3
+    { id: sys_unlink                    [ 87] } hitcount:          3
+    { id: sys_rename                    [ 82] } hitcount:          4
+    { id: unknown_syscall               [ 58] } hitcount:          4
+    { id: sys_connect                   [ 42] } hitcount:          4
+    { id: sys_getpid                    [ 39] } hitcount:          4
+    .
+    .
+    .
+    { id: sys_rt_sigprocmask            [ 14] } hitcount:        952
+    { id: sys_futex                     [202] } hitcount:       1534
+    { id: sys_write                     [  1] } hitcount:       2689
+    { id: sys_setitimer                 [ 38] } hitcount:       2797
+    { id: sys_read                      [  0] } hitcount:       3202
+    { id: sys_select                    [ 23] } hitcount:       3773
+    { id: sys_writev                    [ 20] } hitcount:       4531
+    { id: sys_poll                      [  7] } hitcount:       8314
+    { id: sys_recvmsg                   [ 47] } hitcount:      13738
+    { id: sys_ioctl                     [ 16] } hitcount:      21843
+
+    Totals:
+        Hits: 67612
+        Entries: 72
+        Dropped: 0
+
+    The syscall counts above provide a rough overall picture of system
+    call activity on the system; we can see for example that the most
+    popular system call on this system was the 'sys_ioctl' system call.
+
+    We can use 'compound' keys to refine that number and provide some
+    further insight as to which processes exactly contribute to the
+    overall ioctl count.
+
+    The command below keeps a hitcount for every unique combination of
+    system call id and pid - the end result is essentially a table
+    that keeps a per-pid sum of system call hits.  The results are
+    sorted using the system call id as the primary key, and the
+    hitcount sum as the secondary key:
+
+    # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \
+           /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
+
+    # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
+    # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active]
+
+    { id: sys_read                      [  0], common_pid: rtkit-daemon    [      1877] } hitcount:          1
+    { id: sys_read                      [  0], common_pid: gdbus           [      2976] } hitcount:          1
+    { id: sys_read                      [  0], common_pid: console-kit-dae [      3400] } hitcount:          1
+    { id: sys_read                      [  0], common_pid: postgres        [      1865] } hitcount:          1
+    { id: sys_read                      [  0], common_pid: deja-dup-monito [      3543] } hitcount:          2
+    { id: sys_read                      [  0], common_pid: NetworkManager  [       890] } hitcount:          2
+    { id: sys_read                      [  0], common_pid: evolution-calen [      3048] } hitcount:          2
+    { id: sys_read                      [  0], common_pid: postgres        [      1864] } hitcount:          2
+    { id: sys_read                      [  0], common_pid: nm-applet       [      3022] } hitcount:          2
+    { id: sys_read                      [  0], common_pid: whoopsie        [      1212] } hitcount:          2
+    .
+    .
+    .
+    { id: sys_ioctl                     [ 16], common_pid: bash            [      8479] } hitcount:          1
+    { id: sys_ioctl                     [ 16], common_pid: bash            [      3472] } hitcount:         12
+    { id: sys_ioctl                     [ 16], common_pid: gnome-terminal  [      3199] } hitcount:         16
+    { id: sys_ioctl                     [ 16], common_pid: Xorg            [      1267] } hitcount:       1808
+    { id: sys_ioctl                     [ 16], common_pid: compiz          [      2994] } hitcount:       5580
+    .
+    .
+    .
+    { id: sys_waitid                    [247], common_pid: upstart-dbus-br [      2690] } hitcount:          3
+    { id: sys_waitid                    [247], common_pid: upstart-dbus-br [      2688] } hitcount:         16
+    { id: sys_inotify_add_watch         [254], common_pid: gmain           [       975] } hitcount:          2
+    { id: sys_inotify_add_watch         [254], common_pid: gmain           [      3204] } hitcount:          4
+    { id: sys_inotify_add_watch         [254], common_pid: gmain           [      2888] } hitcount:          4
+    { id: sys_inotify_add_watch         [254], common_pid: gmain           [      3003] } hitcount:          4
+    { id: sys_inotify_add_watch         [254], common_pid: gmain           [      2873] } hitcount:          4
+    { id: sys_inotify_add_watch         [254], common_pid: gmain           [      3196] } hitcount:          6
+    { id: sys_openat                    [257], common_pid: java            [      2623] } hitcount:          2
+    { id: sys_eventfd2                  [290], common_pid: ibus-ui-gtk3    [      2760] } hitcount:          4
+    { id: sys_eventfd2                  [290], common_pid: compiz          [      2994] } hitcount:          6
+
+    Totals:
+        Hits: 31536
+        Entries: 323
+        Dropped: 0
+
+    The above list does give us a breakdown of the ioctl syscall by
+    pid, but it also gives us quite a bit more than that, which we
+    don't really care about at the moment.  Since we know the syscall
+    id for sys_ioctl (16, displayed next to the sys_ioctl name), we
+    can use that to filter out all the other syscalls:
+
+    # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \
+           /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
+
+    # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
+    # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active]
+
+    { id: sys_ioctl                     [ 16], common_pid: gmain           [      2769] } hitcount:          1
+    { id: sys_ioctl                     [ 16], common_pid: evolution-addre [      8571] } hitcount:          1
+    { id: sys_ioctl                     [ 16], common_pid: gmain           [      3003] } hitcount:          1
+    { id: sys_ioctl                     [ 16], common_pid: gmain           [      2781] } hitcount:          1
+    { id: sys_ioctl                     [ 16], common_pid: gmain           [      2829] } hitcount:          1
+    { id: sys_ioctl                     [ 16], common_pid: bash            [      8726] } hitcount:          1
+    { id: sys_ioctl                     [ 16], common_pid: bash            [      8508] } hitcount:          1
+    { id: sys_ioctl                     [ 16], common_pid: gmain           [      2970] } hitcount:          1
+    { id: sys_ioctl                     [ 16], common_pid: gmain           [      2768] } hitcount:          1
+    .
+    .
+    .
+    { id: sys_ioctl                     [ 16], common_pid: pool            [      8559] } hitcount:         45
+    { id: sys_ioctl                     [ 16], common_pid: pool            [      8555] } hitcount:         48
+    { id: sys_ioctl                     [ 16], common_pid: pool            [      8551] } hitcount:         48
+    { id: sys_ioctl                     [ 16], common_pid: avahi-daemon    [       896] } hitcount:         66
+    { id: sys_ioctl                     [ 16], common_pid: Xorg            [      1267] } hitcount:      26674
+    { id: sys_ioctl                     [ 16], common_pid: compiz          [      2994] } hitcount:      73443
+
+    Totals:
+        Hits: 101162
+        Entries: 103
+        Dropped: 0
+
+    The above output shows that 'compiz' and 'Xorg' are far and away
+    the heaviest ioctl callers (which might lead to questions about
+    whether they really need to be making all those calls and to
+    possible avenues for further investigation.)
+
+    The compound key examples used a key and a sum value (hitcount) to
+    sort the output, but we can just as easily use two keys instead.
+    Here's an example where we use a compound key composed of the the
+    common_pid and size event fields.  Sorting with pid as the primary
+    key and 'size' as the secondary key allows us to display an
+    ordered summary of the recvfrom sizes, with counts, received by
+    each process:
+
+    # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \
+           /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger
+
+    # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist
+    # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active]
+
+    { common_pid: smbd            [       784], size:          4 } hitcount:          1
+    { common_pid: dnsmasq         [      1412], size:       4096 } hitcount:        672
+    { common_pid: postgres        [      1796], size:       1000 } hitcount:          6
+    { common_pid: postgres        [      1867], size:       1000 } hitcount:         10
+    { common_pid: bamfdaemon      [      2787], size:         28 } hitcount:          2
+    { common_pid: bamfdaemon      [      2787], size:      14360 } hitcount:          1
+    { common_pid: compiz          [      2994], size:          8 } hitcount:          1
+    { common_pid: compiz          [      2994], size:         20 } hitcount:         11
+    { common_pid: gnome-terminal  [      3199], size:          4 } hitcount:          2
+    { common_pid: firefox         [      8817], size:          4 } hitcount:          1
+    { common_pid: firefox         [      8817], size:          8 } hitcount:          5
+    { common_pid: firefox         [      8817], size:        588 } hitcount:          2
+    { common_pid: firefox         [      8817], size:        628 } hitcount:          1
+    { common_pid: firefox         [      8817], size:       6944 } hitcount:          1
+    { common_pid: firefox         [      8817], size:     408880 } hitcount:          2
+    { common_pid: firefox         [      8822], size:          8 } hitcount:          2
+    { common_pid: firefox         [      8822], size:        160 } hitcount:          2
+    { common_pid: firefox         [      8822], size:        320 } hitcount:          2
+    { common_pid: firefox         [      8822], size:        352 } hitcount:          1
+    .
+    .
+    .
+    { common_pid: pool            [      8923], size:       1960 } hitcount:         10
+    { common_pid: pool            [      8923], size:       2048 } hitcount:         10
+    { common_pid: pool            [      8924], size:       1960 } hitcount:         10
+    { common_pid: pool            [      8924], size:       2048 } hitcount:         10
+    { common_pid: pool            [      8928], size:       1964 } hitcount:          4
+    { common_pid: pool            [      8928], size:       1965 } hitcount:          2
+    { common_pid: pool            [      8928], size:       2048 } hitcount:          6
+    { common_pid: pool            [      8929], size:       1982 } hitcount:          1
+    { common_pid: pool            [      8929], size:       2048 } hitcount:          1
+
+    Totals:
+        Hits: 2016
+        Entries: 224
+        Dropped: 0
+
+  The above example also illustrates the fact that although a compound
+  key is treated as a single entity for hashing purposes, the sub-keys
+  it's composed of can be accessed independently.
+
+  The next example uses a string field as the hash key and
+  demonstrates how you can manually pause and continue a hist trigger.
+  In this example, we'll aggregate fork counts and don't expect a
+  large number of entries in the hash table, so we'll drop it to a
+  much smaller number, say 256:
+
+    # echo 'hist:key=child_comm:val=hitcount:size=256' > \
+           /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+
+    # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+    # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
+
+    { child_comm: dconf worker                        } hitcount:          1
+    { child_comm: ibus-daemon                         } hitcount:          1
+    { child_comm: whoopsie                            } hitcount:          1
+    { child_comm: smbd                                } hitcount:          1
+    { child_comm: gdbus                               } hitcount:          1
+    { child_comm: kthreadd                            } hitcount:          1
+    { child_comm: dconf worker                        } hitcount:          1
+    { child_comm: evolution-alarm                     } hitcount:          2
+    { child_comm: Socket Thread                       } hitcount:          2
+    { child_comm: postgres                            } hitcount:          2
+    { child_comm: bash                                } hitcount:          3
+    { child_comm: compiz                              } hitcount:          3
+    { child_comm: evolution-sourc                     } hitcount:          4
+    { child_comm: dhclient                            } hitcount:          4
+    { child_comm: pool                                } hitcount:          5
+    { child_comm: nm-dispatcher.a                     } hitcount:          8
+    { child_comm: firefox                             } hitcount:          8
+    { child_comm: dbus-daemon                         } hitcount:          8
+    { child_comm: glib-pacrunner                      } hitcount:         10
+    { child_comm: evolution                           } hitcount:         23
+
+    Totals:
+        Hits: 89
+        Entries: 20
+        Dropped: 0
+
+  If we want to pause the hist trigger, we can simply append :pause to
+  the command that started the trigger.  Notice that the trigger info
+  displays as [paused]:
+
+    # echo 'hist:key=child_comm:val=hitcount:size=256:pause' >> \
+           /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+
+    # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+    # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [paused]
+
+    { child_comm: dconf worker                        } hitcount:          1
+    { child_comm: kthreadd                            } hitcount:          1
+    { child_comm: dconf worker                        } hitcount:          1
+    { child_comm: gdbus                               } hitcount:          1
+    { child_comm: ibus-daemon                         } hitcount:          1
+    { child_comm: Socket Thread                       } hitcount:          2
+    { child_comm: evolution-alarm                     } hitcount:          2
+    { child_comm: smbd                                } hitcount:          2
+    { child_comm: bash                                } hitcount:          3
+    { child_comm: whoopsie                            } hitcount:          3
+    { child_comm: compiz                              } hitcount:          3
+    { child_comm: evolution-sourc                     } hitcount:          4
+    { child_comm: pool                                } hitcount:          5
+    { child_comm: postgres                            } hitcount:          6
+    { child_comm: firefox                             } hitcount:          8
+    { child_comm: dhclient                            } hitcount:         10
+    { child_comm: emacs                               } hitcount:         12
+    { child_comm: dbus-daemon                         } hitcount:         20
+    { child_comm: nm-dispatcher.a                     } hitcount:         20
+    { child_comm: evolution                           } hitcount:         35
+    { child_comm: glib-pacrunner                      } hitcount:         59
+
+    Totals:
+        Hits: 199
+        Entries: 21
+        Dropped: 0
+
+  To manually continue having the trigger aggregate events, append
+  :cont instead.  Notice that the trigger info displays as [active]
+  again, and the data has changed:
+
+    # echo 'hist:key=child_comm:val=hitcount:size=256:cont' >> \
+           /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+
+    # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+    # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
+
+    { child_comm: dconf worker                        } hitcount:          1
+    { child_comm: dconf worker                        } hitcount:          1
+    { child_comm: kthreadd                            } hitcount:          1
+    { child_comm: gdbus                               } hitcount:          1
+    { child_comm: ibus-daemon                         } hitcount:          1
+    { child_comm: Socket Thread                       } hitcount:          2
+    { child_comm: evolution-alarm                     } hitcount:          2
+    { child_comm: smbd                                } hitcount:          2
+    { child_comm: whoopsie                            } hitcount:          3
+    { child_comm: compiz                              } hitcount:          3
+    { child_comm: evolution-sourc                     } hitcount:          4
+    { child_comm: bash                                } hitcount:          5
+    { child_comm: pool                                } hitcount:          5
+    { child_comm: postgres                            } hitcount:          6
+    { child_comm: firefox                             } hitcount:          8
+    { child_comm: dhclient                            } hitcount:         11
+    { child_comm: emacs                               } hitcount:         12
+    { child_comm: dbus-daemon                         } hitcount:         22
+    { child_comm: nm-dispatcher.a                     } hitcount:         22
+    { child_comm: evolution                           } hitcount:         35
+    { child_comm: glib-pacrunner                      } hitcount:         59
+
+    Totals:
+        Hits: 206
+        Entries: 21
+        Dropped: 0
+
+  The previous example showed how to start and stop a hist trigger by
+  appending 'pause' and 'continue' to the hist trigger command.  A
+  hist trigger can also be started in a paused state by initially
+  starting the trigger with ':pause' appended.  This allows you to
+  start the trigger only when you're ready to start collecting data
+  and not before.  For example, you could start the trigger in a
+  paused state, then unpause it and do something you want to measure,
+  then pause the trigger again when done.
+
+  Of course, doing this manually can be difficult and error-prone, but
+  it is possible to automatically start and stop a hist trigger based
+  on some condition, via the enable_hist and disable_hist triggers.
+
+  For example, suppose we wanted to take a look at the relative
+  weights in terms of skb length for each callpath that leads to a
+  netif_receieve_skb event when downloading a decent-sized file using
+  wget.
+
+  First we set up an initially paused stacktrace trigger on the
+  netif_receive_skb event:
+
+    # echo 'hist:key=stacktrace:vals=len:pause' > \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+  Next, we set up an 'enable_hist' trigger on the sched_process_exec
+  event, with an 'if filename==/usr/bin/wget' filter.  The effect of
+  this new trigger is that it will 'unpause' the hist trigger we just
+  set up on netif_receive_skb if and only if it sees a
+  sched_process_exec event with a filename of '/usr/bin/wget'.  When
+  that happens, all netif_receive_skb events are aggregated into a
+  hash table keyed on stacktrace:
+
+    # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
+           /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+
+  The aggregation continues until the netif_receive_skb is paused
+  again, which is what the following disable_hist event does by
+  creating a similar setup on the sched_process_exit event, using the
+  filter 'comm==wget':
+
+    # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
+           /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+
+  Whenever a process exits and the comm field of the disable_hist
+  trigger filter matches 'comm==wget', the netif_receive_skb hist
+  trigger is disabled.
+
+  The overall effect is that netif_receive_skb events are aggregated
+  into the hash table for only the duration of the wget.  Executing a
+  wget command and then listing the 'hist' file will display the
+  output generated by the wget command:
+
+    $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
+
+    # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
+    # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
+
+    { stacktrace:
+         __netif_receive_skb_core+0x46d/0x990
+         __netif_receive_skb+0x18/0x60
+         netif_receive_skb_internal+0x23/0x90
+         napi_gro_receive+0xc8/0x100
+         ieee80211_deliver_skb+0xd6/0x270 [mac80211]
+         ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
+         ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
+         ieee80211_rx+0x31d/0x900 [mac80211]
+         iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
+         iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
+         iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
+         irq_thread_fn+0x20/0x50
+         irq_thread+0x11f/0x150
+         kthread+0xd2/0xf0
+         ret_from_fork+0x42/0x70
+    } hitcount:         85  len:      28884
+    { stacktrace:
+         __netif_receive_skb_core+0x46d/0x990
+         __netif_receive_skb+0x18/0x60
+         netif_receive_skb_internal+0x23/0x90
+         napi_gro_complete+0xa4/0xe0
+         dev_gro_receive+0x23a/0x360
+         napi_gro_receive+0x30/0x100
+         ieee80211_deliver_skb+0xd6/0x270 [mac80211]
+         ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
+         ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
+         ieee80211_rx+0x31d/0x900 [mac80211]
+         iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
+         iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
+         iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
+         irq_thread_fn+0x20/0x50
+         irq_thread+0x11f/0x150
+         kthread+0xd2/0xf0
+    } hitcount:         98  len:     664329
+    { stacktrace:
+         __netif_receive_skb_core+0x46d/0x990
+         __netif_receive_skb+0x18/0x60
+         process_backlog+0xa8/0x150
+         net_rx_action+0x15d/0x340
+         __do_softirq+0x114/0x2c0
+         do_softirq_own_stack+0x1c/0x30
+         do_softirq+0x65/0x70
+         __local_bh_enable_ip+0xb5/0xc0
+         ip_finish_output+0x1f4/0x840
+         ip_output+0x6b/0xc0
+         ip_local_out_sk+0x31/0x40
+         ip_send_skb+0x1a/0x50
+         udp_send_skb+0x173/0x2a0
+         udp_sendmsg+0x2bf/0x9f0
+         inet_sendmsg+0x64/0xa0
+         sock_sendmsg+0x3d/0x50
+    } hitcount:        115  len:      13030
+    { stacktrace:
+         __netif_receive_skb_core+0x46d/0x990
+         __netif_receive_skb+0x18/0x60
+         netif_receive_skb_internal+0x23/0x90
+         napi_gro_complete+0xa4/0xe0
+         napi_gro_flush+0x6d/0x90
+         iwl_pcie_irq_handler+0x92a/0x12f0 [iwlwifi]
+         irq_thread_fn+0x20/0x50
+         irq_thread+0x11f/0x150
+         kthread+0xd2/0xf0
+         ret_from_fork+0x42/0x70
+    } hitcount:        934  len:    5512212
+
+    Totals:
+        Hits: 1232
+        Entries: 4
+        Dropped: 0
+
+  The above shows all the netif_receive_skb callpaths and their total
+  lengths for the duration of the wget command.
+
+  The 'clear' hist trigger param can be used to clear the hash table.
+  Suppose we wanted to try another run of the previous example but
+  this time also wanted to see the complete list of events that went
+  into the histogram.  In order to avoid having to set everything up
+  again, we can just clear the histogram first:
+
+    # echo 'hist:key=stacktrace:vals=len:clear' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+  Just to verify that it is in fact cleared, here's what we now see in
+  the hist file:
+
+    # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
+    # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
+
+    Totals:
+        Hits: 0
+        Entries: 0
+        Dropped: 0
+
+  Since we want to see the detailed list of every netif_receive_skb
+  event occurring during the new run, which are in fact the same
+  events being aggregated into the hash table, we add some additional
+  'enable_event' events to the triggering sched_process_exec and
+  sched_process_exit events as such:
+
+    # echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \
+           /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+
+    # echo 'disable_event:net:netif_receive_skb if comm==wget' > \
+           /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+
+  If you read the trigger files for the sched_process_exec and
+  sched_process_exit triggers, you should see two triggers for each:
+  one enabling/disabling the hist aggregation and the other
+  enabling/disabling the logging of events:
+
+    # cat /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+    enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
+    enable_hist:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
+
+    # cat /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+    enable_event:net:netif_receive_skb:unlimited if comm==wget
+    disable_hist:net:netif_receive_skb:unlimited if comm==wget
+
+  In other words, whenever either of the sched_process_exec or
+  sched_process_exit events is hit and matches 'wget', it enables or
+  disables both the histogram and the event log, and what you end up
+  with is a hash table and set of events just covering the specified
+  duration.  Run the wget command again:
+
+    $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
+
+  Displaying the 'hist' file should show something similar to what you
+  saw in the last run, but this time you should also see the
+  individual events in the trace file:
+
+    # cat /sys/kernel/debug/tracing/trace
+
+    # tracer: nop
+    #
+    # entries-in-buffer/entries-written: 183/1426   #P:4
+    #
+    #                              _-----=> irqs-off
+    #                             / _----=> need-resched
+    #                            | / _---=> hardirq/softirq
+    #                            || / _--=> preempt-depth
+    #                            ||| /     delay
+    #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+    #              | |       |   ||||       |         |
+                wget-15108 [000] ..s1 31769.606929: netif_receive_skb: dev=lo skbaddr=ffff88009c353100 len=60
+                wget-15108 [000] ..s1 31769.606999: netif_receive_skb: dev=lo skbaddr=ffff88009c353200 len=60
+             dnsmasq-1382  [000] ..s1 31769.677652: netif_receive_skb: dev=lo skbaddr=ffff88009c352b00 len=130
+             dnsmasq-1382  [000] ..s1 31769.685917: netif_receive_skb: dev=lo skbaddr=ffff88009c352200 len=138
+    ##### CPU 2 buffer started ####
+      irq/29-iwlwifi-559   [002] ..s. 31772.031529: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433d00 len=2948
+      irq/29-iwlwifi-559   [002] ..s. 31772.031572: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432200 len=1500
+      irq/29-iwlwifi-559   [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948
+      irq/29-iwlwifi-559   [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948
+      irq/29-iwlwifi-559   [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500
+    .
+    .
+    .
+
+  The following example demonstrates how multiple hist triggers can be
+  attached to a given event.  This capability can be useful for
+  creating a set of different summaries derived from the same set of
+  events, or for comparing the effects of different filters, among
+  other things.
+
+    # echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+    # echo 'hist:keys=skbaddr.hex:vals=len if len > 4096' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+    # echo 'hist:keys=skbaddr.hex:vals=len if len == 256' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+    # echo 'hist:keys=skbaddr.hex:vals=len' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+    # echo 'hist:keys=len:vals=common_preempt_count' >> \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+  The above set of commands create four triggers differing only in
+  their filters, along with a completely different though fairly
+  nonsensical trigger.  Note that in order to append multiple hist
+  triggers to the same file, you should use the '>>' operator to
+  append them ('>' will also add the new hist trigger, but will remove
+  any existing hist triggers beforehand).
+
+  Displaying the contents of the 'hist' file for the event shows the
+  contents of all five histograms:
+
+    # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
+
+    # event histogram
+    #
+    # trigger info: hist:keys=len:vals=hitcount,common_preempt_count:sort=hitcount:size=2048 [active]
+    #
+
+    { len:        176 } hitcount:          1  common_preempt_count:          0
+    { len:        223 } hitcount:          1  common_preempt_count:          0
+    { len:       4854 } hitcount:          1  common_preempt_count:          0
+    { len:        395 } hitcount:          1  common_preempt_count:          0
+    { len:        177 } hitcount:          1  common_preempt_count:          0
+    { len:        446 } hitcount:          1  common_preempt_count:          0
+    { len:       1601 } hitcount:          1  common_preempt_count:          0
+    .
+    .
+    .
+    { len:       1280 } hitcount:         66  common_preempt_count:          0
+    { len:        116 } hitcount:         81  common_preempt_count:         40
+    { len:        708 } hitcount:        112  common_preempt_count:          0
+    { len:         46 } hitcount:        221  common_preempt_count:          0
+    { len:       1264 } hitcount:        458  common_preempt_count:          0
+
+    Totals:
+        Hits: 1428
+        Entries: 147
+        Dropped: 0
+
+
+    # event histogram
+    #
+    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
+    #
+
+    { skbaddr: ffff8800baee5e00 } hitcount:          1  len:        130
+    { skbaddr: ffff88005f3d5600 } hitcount:          1  len:       1280
+    { skbaddr: ffff88005f3d4900 } hitcount:          1  len:       1280
+    { skbaddr: ffff88009fed6300 } hitcount:          1  len:        115
+    { skbaddr: ffff88009fe0ad00 } hitcount:          1  len:        115
+    { skbaddr: ffff88008cdb1900 } hitcount:          1  len:         46
+    { skbaddr: ffff880064b5ef00 } hitcount:          1  len:        118
+    { skbaddr: ffff880044e3c700 } hitcount:          1  len:         60
+    { skbaddr: ffff880100065900 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d46bd500 } hitcount:          1  len:        116
+    { skbaddr: ffff88005f3d5f00 } hitcount:          1  len:       1280
+    { skbaddr: ffff880100064700 } hitcount:          1  len:        365
+    { skbaddr: ffff8800badb6f00 } hitcount:          1  len:         60
+    .
+    .
+    .
+    { skbaddr: ffff88009fe0be00 } hitcount:         27  len:      24677
+    { skbaddr: ffff88009fe0a400 } hitcount:         27  len:      23052
+    { skbaddr: ffff88009fe0b700 } hitcount:         31  len:      25589
+    { skbaddr: ffff88009fe0b600 } hitcount:         32  len:      27326
+    { skbaddr: ffff88006a462800 } hitcount:         68  len:      71678
+    { skbaddr: ffff88006a463700 } hitcount:         70  len:      72678
+    { skbaddr: ffff88006a462b00 } hitcount:         71  len:      77589
+    { skbaddr: ffff88006a463600 } hitcount:         73  len:      71307
+    { skbaddr: ffff88006a462200 } hitcount:         81  len:      81032
+
+    Totals:
+        Hits: 1451
+        Entries: 318
+        Dropped: 0
+
+
+    # event histogram
+    #
+    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len == 256 [active]
+    #
+
+
+    Totals:
+        Hits: 0
+        Entries: 0
+        Dropped: 0
+
+
+    # event histogram
+    #
+    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len > 4096 [active]
+    #
+
+    { skbaddr: ffff88009fd2c300 } hitcount:          1  len:       7212
+    { skbaddr: ffff8800d2bcce00 } hitcount:          1  len:       7212
+    { skbaddr: ffff8800d2bcd700 } hitcount:          1  len:       7212
+    { skbaddr: ffff8800d2bcda00 } hitcount:          1  len:      21492
+    { skbaddr: ffff8800ae2e2d00 } hitcount:          1  len:       7212
+    { skbaddr: ffff8800d2bcdb00 } hitcount:          1  len:       7212
+    { skbaddr: ffff88006a4df500 } hitcount:          1  len:       4854
+    { skbaddr: ffff88008ce47b00 } hitcount:          1  len:      18636
+    { skbaddr: ffff8800ae2e2200 } hitcount:          1  len:      12924
+    { skbaddr: ffff88005f3e1000 } hitcount:          1  len:       4356
+    { skbaddr: ffff8800d2bcdc00 } hitcount:          2  len:      24420
+    { skbaddr: ffff8800d2bcc200 } hitcount:          2  len:      12996
+
+    Totals:
+        Hits: 14
+        Entries: 12
+        Dropped: 0
+
+
+    # event histogram
+    #
+    # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len < 0 [active]
+    #
+
+
+    Totals:
+        Hits: 0
+        Entries: 0
+        Dropped: 0
+
+  Named triggers can be used to have triggers share a common set of
+  histogram data.  This capability is mostly useful for combining the
+  output of events generated by tracepoints contained inside inline
+  functions, but names can be used in a hist trigger on any event.
+  For example, these two triggers when hit will update the same 'len'
+  field in the shared 'foo' histogram data:
+
+    # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
+           /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+    # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
+           /sys/kernel/debug/tracing/events/net/netif_rx/trigger
+
+  You can see that they're updating common histogram data by reading
+  each event's hist files at the same time:
+
+    # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist;
+      cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
+
+    # event histogram
+    #
+    # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
+    #
+
+    { skbaddr: ffff88000ad53500 } hitcount:          1  len:         46
+    { skbaddr: ffff8800af5a1500 } hitcount:          1  len:         76
+    { skbaddr: ffff8800d62a1900 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d2bccb00 } hitcount:          1  len:        468
+    { skbaddr: ffff8800d3c69900 } hitcount:          1  len:         46
+    { skbaddr: ffff88009ff09100 } hitcount:          1  len:         52
+    { skbaddr: ffff88010f13ab00 } hitcount:          1  len:        168
+    { skbaddr: ffff88006a54f400 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d2bcc500 } hitcount:          1  len:        260
+    { skbaddr: ffff880064505000 } hitcount:          1  len:         46
+    { skbaddr: ffff8800baf24e00 } hitcount:          1  len:         32
+    { skbaddr: ffff88009fe0ad00 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d3edff00 } hitcount:          1  len:         44
+    { skbaddr: ffff88009fe0b400 } hitcount:          1  len:        168
+    { skbaddr: ffff8800a1c55a00 } hitcount:          1  len:         40
+    { skbaddr: ffff8800d2bcd100 } hitcount:          1  len:         40
+    { skbaddr: ffff880064505f00 } hitcount:          1  len:        174
+    { skbaddr: ffff8800a8bff200 } hitcount:          1  len:        160
+    { skbaddr: ffff880044e3cc00 } hitcount:          1  len:         76
+    { skbaddr: ffff8800a8bfe700 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d2bcdc00 } hitcount:          1  len:         32
+    { skbaddr: ffff8800a1f64800 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d2bcde00 } hitcount:          1  len:        988
+    { skbaddr: ffff88006a5dea00 } hitcount:          1  len:         46
+    { skbaddr: ffff88002e37a200 } hitcount:          1  len:         44
+    { skbaddr: ffff8800a1f32c00 } hitcount:          2  len:        676
+    { skbaddr: ffff88000ad52600 } hitcount:          2  len:        107
+    { skbaddr: ffff8800a1f91e00 } hitcount:          2  len:         92
+    { skbaddr: ffff8800af5a0200 } hitcount:          2  len:        142
+    { skbaddr: ffff8800d2bcc600 } hitcount:          2  len:        220
+    { skbaddr: ffff8800ba36f500 } hitcount:          2  len:         92
+    { skbaddr: ffff8800d021f800 } hitcount:          2  len:         92
+    { skbaddr: ffff8800a1f33600 } hitcount:          2  len:        675
+    { skbaddr: ffff8800a8bfff00 } hitcount:          3  len:        138
+    { skbaddr: ffff8800d62a1300 } hitcount:          3  len:        138
+    { skbaddr: ffff88002e37a100 } hitcount:          4  len:        184
+    { skbaddr: ffff880064504400 } hitcount:          4  len:        184
+    { skbaddr: ffff8800a8bfec00 } hitcount:          4  len:        184
+    { skbaddr: ffff88000ad53700 } hitcount:          5  len:        230
+    { skbaddr: ffff8800d2bcdb00 } hitcount:          5  len:        196
+    { skbaddr: ffff8800a1f90000 } hitcount:          6  len:        276
+    { skbaddr: ffff88006a54f900 } hitcount:          6  len:        276
+
+    Totals:
+        Hits: 81
+        Entries: 42
+        Dropped: 0
+    # event histogram
+    #
+    # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
+    #
+
+    { skbaddr: ffff88000ad53500 } hitcount:          1  len:         46
+    { skbaddr: ffff8800af5a1500 } hitcount:          1  len:         76
+    { skbaddr: ffff8800d62a1900 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d2bccb00 } hitcount:          1  len:        468
+    { skbaddr: ffff8800d3c69900 } hitcount:          1  len:         46
+    { skbaddr: ffff88009ff09100 } hitcount:          1  len:         52
+    { skbaddr: ffff88010f13ab00 } hitcount:          1  len:        168
+    { skbaddr: ffff88006a54f400 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d2bcc500 } hitcount:          1  len:        260
+    { skbaddr: ffff880064505000 } hitcount:          1  len:         46
+    { skbaddr: ffff8800baf24e00 } hitcount:          1  len:         32
+    { skbaddr: ffff88009fe0ad00 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d3edff00 } hitcount:          1  len:         44
+    { skbaddr: ffff88009fe0b400 } hitcount:          1  len:        168
+    { skbaddr: ffff8800a1c55a00 } hitcount:          1  len:         40
+    { skbaddr: ffff8800d2bcd100 } hitcount:          1  len:         40
+    { skbaddr: ffff880064505f00 } hitcount:          1  len:        174
+    { skbaddr: ffff8800a8bff200 } hitcount:          1  len:        160
+    { skbaddr: ffff880044e3cc00 } hitcount:          1  len:         76
+    { skbaddr: ffff8800a8bfe700 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d2bcdc00 } hitcount:          1  len:         32
+    { skbaddr: ffff8800a1f64800 } hitcount:          1  len:         46
+    { skbaddr: ffff8800d2bcde00 } hitcount:          1  len:        988
+    { skbaddr: ffff88006a5dea00 } hitcount:          1  len:         46
+    { skbaddr: ffff88002e37a200 } hitcount:          1  len:         44
+    { skbaddr: ffff8800a1f32c00 } hitcount:          2  len:        676
+    { skbaddr: ffff88000ad52600 } hitcount:          2  len:        107
+    { skbaddr: ffff8800a1f91e00 } hitcount:          2  len:         92
+    { skbaddr: ffff8800af5a0200 } hitcount:          2  len:        142
+    { skbaddr: ffff8800d2bcc600 } hitcount:          2  len:        220
+    { skbaddr: ffff8800ba36f500 } hitcount:          2  len:         92
+    { skbaddr: ffff8800d021f800 } hitcount:          2  len:         92
+    { skbaddr: ffff8800a1f33600 } hitcount:          2  len:        675
+    { skbaddr: ffff8800a8bfff00 } hitcount:          3  len:        138
+    { skbaddr: ffff8800d62a1300 } hitcount:          3  len:        138
+    { skbaddr: ffff88002e37a100 } hitcount:          4  len:        184
+    { skbaddr: ffff880064504400 } hitcount:          4  len:        184
+    { skbaddr: ffff8800a8bfec00 } hitcount:          4  len:        184
+    { skbaddr: ffff88000ad53700 } hitcount:          5  len:        230
+    { skbaddr: ffff8800d2bcdb00 } hitcount:          5  len:        196
+    { skbaddr: ffff8800a1f90000 } hitcount:          6  len:        276
+    { skbaddr: ffff88006a54f900 } hitcount:          6  len:        276
+
+    Totals:
+        Hits: 81
+        Entries: 42
+        Dropped: 0
+
+  And here's an example that shows how to combine histogram data from
+  any two events even if they don't share any 'compatible' fields
+  other than 'hitcount' and 'stacktrace'.  These commands create a
+  couple of triggers named 'bar' using those fields:
+
+    # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
+           /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+    # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
+          /sys/kernel/debug/tracing/events/net/netif_rx/trigger
+
+  And displaying the output of either shows some interesting if
+  somewhat confusing output:
+
+    # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+    # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
+
+    # event histogram
+    #
+    # trigger info: hist:name=bar:keys=stacktrace:vals=hitcount:sort=hitcount:size=2048 [active]
+    #
+
+    { stacktrace:
+             _do_fork+0x18e/0x330
+             kernel_thread+0x29/0x30
+             kthreadd+0x154/0x1b0
+             ret_from_fork+0x3f/0x70
+    } hitcount:          1
+    { stacktrace:
+             netif_rx_internal+0xb2/0xd0
+             netif_rx_ni+0x20/0x70
+             dev_loopback_xmit+0xaa/0xd0
+             ip_mc_output+0x126/0x240
+             ip_local_out_sk+0x31/0x40
+             igmp_send_report+0x1e9/0x230
+             igmp_timer_expire+0xe9/0x120
+             call_timer_fn+0x39/0xf0
+             run_timer_softirq+0x1e1/0x290
+             __do_softirq+0xfd/0x290
+             irq_exit+0x98/0xb0
+             smp_apic_timer_interrupt+0x4a/0x60
+             apic_timer_interrupt+0x6d/0x80
+             cpuidle_enter+0x17/0x20
+             call_cpuidle+0x3b/0x60
+             cpu_startup_entry+0x22d/0x310
+    } hitcount:          1
+    { stacktrace:
+             netif_rx_internal+0xb2/0xd0
+             netif_rx_ni+0x20/0x70
+             dev_loopback_xmit+0xaa/0xd0
+             ip_mc_output+0x17f/0x240
+             ip_local_out_sk+0x31/0x40
+             ip_send_skb+0x1a/0x50
+             udp_send_skb+0x13e/0x270
+             udp_sendmsg+0x2bf/0x980
+             inet_sendmsg+0x67/0xa0
+             sock_sendmsg+0x38/0x50
+             SYSC_sendto+0xef/0x170
+             SyS_sendto+0xe/0x10
+             entry_SYSCALL_64_fastpath+0x12/0x6a
+    } hitcount:          2
+    { stacktrace:
+             netif_rx_internal+0xb2/0xd0
+             netif_rx+0x1c/0x60
+             loopback_xmit+0x6c/0xb0
+             dev_hard_start_xmit+0x219/0x3a0
+             __dev_queue_xmit+0x415/0x4f0
+             dev_queue_xmit_sk+0x13/0x20
+             ip_finish_output2+0x237/0x340
+             ip_finish_output+0x113/0x1d0
+             ip_output+0x66/0xc0
+             ip_local_out_sk+0x31/0x40
+             ip_send_skb+0x1a/0x50
+             udp_send_skb+0x16d/0x270
+             udp_sendmsg+0x2bf/0x980
+             inet_sendmsg+0x67/0xa0
+             sock_sendmsg+0x38/0x50
+             ___sys_sendmsg+0x14e/0x270
+    } hitcount:         76
+    { stacktrace:
+             netif_rx_internal+0xb2/0xd0
+             netif_rx+0x1c/0x60
+             loopback_xmit+0x6c/0xb0
+             dev_hard_start_xmit+0x219/0x3a0
+             __dev_queue_xmit+0x415/0x4f0
+             dev_queue_xmit_sk+0x13/0x20
+             ip_finish_output2+0x237/0x340
+             ip_finish_output+0x113/0x1d0
+             ip_output+0x66/0xc0
+             ip_local_out_sk+0x31/0x40
+             ip_send_skb+0x1a/0x50
+             udp_send_skb+0x16d/0x270
+             udp_sendmsg+0x2bf/0x980
+             inet_sendmsg+0x67/0xa0
+             sock_sendmsg+0x38/0x50
+             ___sys_sendmsg+0x269/0x270
+    } hitcount:         77
+    { stacktrace:
+             netif_rx_internal+0xb2/0xd0
+             netif_rx+0x1c/0x60
+             loopback_xmit+0x6c/0xb0
+             dev_hard_start_xmit+0x219/0x3a0
+             __dev_queue_xmit+0x415/0x4f0
+             dev_queue_xmit_sk+0x13/0x20
+             ip_finish_output2+0x237/0x340
+             ip_finish_output+0x113/0x1d0
+             ip_output+0x66/0xc0
+             ip_local_out_sk+0x31/0x40
+             ip_send_skb+0x1a/0x50
+             udp_send_skb+0x16d/0x270
+             udp_sendmsg+0x2bf/0x980
+             inet_sendmsg+0x67/0xa0
+             sock_sendmsg+0x38/0x50
+             SYSC_sendto+0xef/0x170
+    } hitcount:         88
+    { stacktrace:
+             _do_fork+0x18e/0x330
+             SyS_clone+0x19/0x20
+             entry_SYSCALL_64_fastpath+0x12/0x6a
+    } hitcount:        244
+
+    Totals:
+        Hits: 489
+        Entries: 7
+        Dropped: 0
+
+
+2.2 Inter-event hist triggers
+-----------------------------
+
+Inter-event hist triggers are hist triggers that combine values from
+one or more other events and create a histogram using that data.  Data
+from an inter-event histogram can in turn become the source for
+further combined histograms, thus providing a chain of related
+histograms, which is important for some applications.
+
+The most important example of an inter-event quantity that can be used
+in this manner is latency, which is simply a difference in timestamps
+between two events.  Although latency is the most important
+inter-event quantity, note that because the support is completely
+general across the trace event subsystem, any event field can be used
+in an inter-event quantity.
+
+An example of a histogram that combines data from other histograms
+into a useful chain would be a 'wakeupswitch latency' histogram that
+combines a 'wakeup latency' histogram and a 'switch latency'
+histogram.
+
+Normally, a hist trigger specification consists of a (possibly
+compound) key along with one or more numeric values, which are
+continually updated sums associated with that key.  A histogram
+specification in this case consists of individual key and value
+specifications that refer to trace event fields associated with a
+single event type.
+
+The inter-event hist trigger extension allows fields from multiple
+events to be referenced and combined into a multi-event histogram
+specification.  In support of this overall goal, a few enabling
+features have been added to the hist trigger support:
+
+  - In order to compute an inter-event quantity, a value from one
+    event needs to saved and then referenced from another event.  This
+    requires the introduction of support for histogram 'variables'.
+
+  - The computation of inter-event quantities and their combination
+    require some minimal amount of support for applying simple
+    expressions to variables (+ and -).
+
+  - A histogram consisting of inter-event quantities isn't logically a
+    histogram on either event (so having the 'hist' file for either
+    event host the histogram output doesn't really make sense).  To
+    address the idea that the histogram is associated with a
+    combination of events, support is added allowing the creation of
+    'synthetic' events that are events derived from other events.
+    These synthetic events are full-fledged events just like any other
+    and can be used as such, as for instance to create the
+    'combination' histograms mentioned previously.
+
+  - A set of 'actions' can be associated with histogram entries -
+    these can be used to generate the previously mentioned synthetic
+    events, but can also be used for other purposes, such as for
+    example saving context when a 'max' latency has been hit.
+
+  - Trace events don't have a 'timestamp' associated with them, but
+    there is an implicit timestamp saved along with an event in the
+    underlying ftrace ring buffer.  This timestamp is now exposed as a
+    a synthetic field named '$common_timestamp' which can be used in
+    histograms as if it were any other event field.  Note that it has
+    a '$' prefixed to it - this is meant to indicate that it isn't an
+    actual field in the trace format but rather is a synthesized value
+    that nonetheless can be used as if it were an actual field.  By
+    default it is in units of nanoseconds; appending '.usecs' to a
+    common_timestamp field changes the units to microseconds.
+
+A note on inter-event timestamps: If $common_timestamp is used in a
+histogram, the trace buffer is automatically switched over to using
+absolute timestamps and the "global" trace clock, in order to avoid
+bogus timestamp differences with other clocks that aren't coherent
+across CPUs.  This can be overridden by specifying one of the other
+trace clocks instead, using the "clock=XXX" hist trigger attribute,
+where XXX is any of the clocks listed in the tracing/trace_clock
+pseudo-file.
+
+These features are described in more detail in the following sections.
+
+2.2.1 Histogram Variables
+-------------------------
+
+Variables are simply named locations used for saving and retrieving
+values between matching events.  A 'matching' event is defined as an
+event that has a matching key - if a variable is saved for a histogram
+entry corresponding to that key, any subsequent event with a matching
+key can access that variable.
+
+A variable's value is normally available to any subsequent event until
+it is set to something else by a subsequent event.  The one exception
+to that rule is that any variable used in an expression is essentially
+'read-once' - once it's used by an expression in a subsequent event,
+it's reset to its 'unset' state, which means it can't be used again
+unless it's set again.  This ensures not only that an event doesn't
+use an uninitialized variable in a calculation, but that that variable
+is used only once and not for any unrelated subsequent match.
+
+The basic syntax for saving a variable is to simply prefix a unique
+variable name not corresponding to any keyword along with an '=' sign
+to any event field.
+
+Either keys or values can be saved and retrieved in this way.  This
+creates a variable named 'ts0' for a histogram entry with the key
+'next_pid':
+
+  # echo 'hist:keys=next_pid:vals=$ts0:ts0=$common_timestamp ... >> \
+	event/trigger
+
+The ts0 variable can be accessed by any subsequent event having the
+same pid as 'next_pid'.
+
+Variable references are formed by prepending the variable name with
+the '$' sign.  Thus for example, the ts0 variable above would be
+referenced as '$ts0' in expressions.
+
+Because 'vals=' is used, the $common_timestamp variable value above
+will also be summed as a normal histogram value would (though for a
+timestamp it makes little sense).
+
+The below shows that a key value can also be saved in the same way:
+
+  # echo 'hist:timer_pid=common_pid:key=timer_pid ...' >> event/trigger
+
+If a variable isn't a key variable or prefixed with 'vals=', the
+associated event field will be saved in a variable but won't be summed
+as a value:
+
+  # echo 'hist:keys=next_pid:ts1=$common_timestamp ... >> event/trigger
+
+Multiple variables can be assigned at the same time.  The below would
+result in both ts0 and b being created as variables, with both
+common_timestamp and field1 additionally being summed as values:
+
+  # echo 'hist:keys=pid:vals=$ts0,$b:ts0=$common_timestamp,b=field1 ... >> \
+	event/trigger
+
+Note that variable assignments can appear either preceding or
+following their use.  The command below behaves identically to the
+command above:
+
+  # echo 'hist:keys=pid:ts0=$common_timestamp,b=field1:vals=$ts0,$b ... >> \
+	event/trigger
+
+Any number of variables not bound to a 'vals=' prefix can also be
+assigned by simply separating them with colons.  Below is the same
+thing but without the values being summed in the histogram:
+
+  # echo 'hist:keys=pid:ts0=$common_timestamp:b=field1 ... >> event/trigger
+
+Variables set as above can be referenced and used in expressions on
+another event.
+
+For example, here's how a latency can be calculated:
+
+  # echo 'hist:keys=pid,prio:ts0=$common_timestamp ... >> event1/trigger
+  # echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp-$ts0 ... >> event2/trigger
+
+In the first line above, the event's timetamp is saved into the
+variable ts0.  In the next line, ts0 is subtracted from the second
+event's timestamp to produce the latency, which is then assigned into
+yet another variable, 'wakeup_lat'.  The hist trigger below in turn
+makes use of the wakeup_lat variable to compute a combined latency
+using the same key and variable from yet another event:
+
+  # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ... >> event3/trigger
+
+2.2.2 Synthetic Events
+----------------------
+
+Synthetic events are user-defined events generated from hist trigger
+variables or fields associated with one or more other events.  Their
+purpose is to provide a mechanism for displaying data spanning
+multiple events consistent with the existing and already familiar
+usage for normal events.
+
+To define a synthetic event, the user writes a simple specification
+consisting of the name of the new event along with one or more
+variables and their types, which can be any valid field type,
+separated by semicolons, to the tracing/synthetic_events file.
+
+For instance, the following creates a new event named 'wakeup_latency'
+with 3 fields: lat, pid, and prio.  Each of those fields is simply a
+variable reference to a variable on another event:
+
+  # echo 'wakeup_latency \
+          u64 lat; \
+          pid_t pid; \
+	  int prio' >> \
+	  /sys/kernel/debug/tracing/synthetic_events
+
+Reading the tracing/synthetic_events file lists all the currently
+defined synthetic events, in this case the event defined above:
+
+  # cat /sys/kernel/debug/tracing/synthetic_events
+    wakeup_latency u64 lat; pid_t pid; int prio
+
+An existing synthetic event definition can be removed by prepending
+the command that defined it with a '!':
+
+  # echo '!wakeup_latency u64 lat pid_t pid int prio' >> \
+    /sys/kernel/debug/tracing/synthetic_events
+
+At this point, there isn't yet an actual 'wakeup_latency' event
+instantiated in the event subsytem - for this to happen, a 'hist
+trigger action' needs to be instantiated and bound to actual fields
+and variables defined on other events (see Section 6.3.3 below).
+
+Once that is done, an event instance is created, and a histogram can
+be defined using it:
+
+  # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \
+        /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
+
+The new event is created under the tracing/events/synthetic/ directory
+and looks and behaves just like any other event:
+
+  # ls /sys/kernel/debug/tracing/events/synthetic/wakeup_latency
+        enable  filter  format  hist  id  trigger
+
+Like any other event, once a histogram is enabled for the event, the
+output can be displayed by reading the event's 'hist' file.
+
+2.2.3 Hist trigger 'actions'
+----------------------------
+
+A hist trigger 'action' is a function that's executed whenever a
+histogram entry is added or updated.
+
+The default 'action' if no special function is explicity specified is
+as it always has been, to simply update the set of values associated
+with an entry.  Some applications, however, may want to perform
+additional actions at that point, such as generate another event, or
+compare and save a maximum.
+
+The following additional actions are available.  To specify an action
+for a given event, simply specify the action between colons in the
+hist trigger specification.
+
+  - onmatch(matching.event).<synthetic_event_name>(param list)
+
+    The 'onmatch(matching.event).<synthetic_event_name>(params)' hist
+    trigger action is invoked whenever an event matches and the
+    histogram entry would be added or updated.  It causes the named
+    synthetic event to be generated with the values given in the
+    'param list'.  The result is the generation of a synthetic event
+    that consists of the values contained in those variables at the
+    time the invoking event was hit.
+
+    The 'param list' consists of one or more parameters which may be
+    either variables or fields defined on either the 'matching.event'
+    or the target event.  The variables or fields specified in the
+    param list may be either fully-qualified or unqualified.  If a
+    variable is specified as unqualified, it must be unique between
+    the two events.  A field name used as a param can be unqualified
+    if it refers to the target event, but must be fully qualified if
+    it refers to the matching event.  A fully-qualified name is of the
+    form 'system.event_name.$var_name' or 'system.event_name.field'.
+
+    The 'matching.event' specification is simply the fully qualified
+    event name of the event that matches the target event for the
+    onmatch() functionality, in the form 'system.event_name'.
+
+    Finally, the number and type of variables/fields in the 'param
+    list' must match the number and types of the fields in the
+    synthetic event being generated.
+
+    As an example the below defines a simple synthetic event and uses
+    a variable defined on the sched_wakeup_new event as a parameter
+    when invoking the synthetic event.  Here we define the synthetic
+    event:
+
+    # echo 'wakeup_new_test pid_t pid' >> \
+           /sys/kernel/debug/tracing/synthetic_events
+
+    # cat /sys/kernel/debug/tracing/synthetic_events
+          wakeup_new_test pid_t pid
+
+    The following hist trigger both defines the missing testpid
+    variable and specifies an onmatch() action that generates a
+    wakeup_new_test synthetic event whenever a sched_wakeup_new event
+    occurs, which because of the 'if comm == "cyclictest"' filter only
+    happens when the executable is cyclictest:
+
+    # echo 'hist:keys=$testpid:testpid=pid:onmatch(sched.sched_wakeup_new).\
+            wakeup_new_test($testpid) if comm=="cyclictest"' >> \
+            /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger
+
+    Creating and displaying a histogram based on those events is now
+    just a matter of using the fields and new synthetic event in the
+    tracing/events/synthetic directory, as usual:
+
+    # echo 'hist:keys=pid:sort=pid' >> \
+           /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/trigger
+
+    Running 'cyclictest' should cause wakeup_new events to generate
+    wakeup_new_test synthetic events which should result in histogram
+    output in the wakeup_new_test event's hist file:
+
+    # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/hist
+
+    A more typical usage would be to use two events to calculate a
+    latency.  The following example uses a set of hist triggers to
+    produce a 'wakeup_latency' histogram:
+
+    First, we define a 'wakeup_latency' synthetic event:
+
+    # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \
+            /sys/kernel/debug/tracing/synthetic_events
+
+    Next, we specify that whenever we see a sched_waking event for a
+    cyclictest thread, save the timestamp in a 'ts0' variable:
+
+    # echo 'hist:keys=$saved_pid:saved_pid=pid:ts0=$common_timestamp.usecs \
+            if comm=="cyclictest"' >> \
+	    /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
+
+    Then, when the corresponding thread is actually scheduled onto the
+    CPU by a sched_switch event, calculate the latency and use that
+    along with another variable and an event field to generate a
+    wakeup_latency synthetic event:
+
+    # echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp.usecs-$ts0:\
+            onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,\
+	            $saved_pid,next_prio) if next_comm=="cyclictest"' >> \
+	    /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
+
+    We also need to create a histogram on the wakeup_latency synthetic
+    event in order to aggregate the generated synthetic event data:
+
+    # echo 'hist:keys=pid,prio,lat:sort=pid,lat' >> \
+            /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
+
+    Finally, once we've run cyclictest to actually generate some
+    events, we can see the output by looking at the wakeup_latency
+    synthetic event's hist file:
+
+    # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist
+
+  - onmax(var).save(field,..	.)
+
+    The 'onmax(var).save(field,...)' hist trigger action is invoked
+    whenever the value of 'var' associated with a histogram entry
+    exceeds the current maximum contained in that variable.
+
+    The end result is that the trace event fields specified as the
+    onmax.save() params will be saved if 'var' exceeds the current
+    maximum for that hist trigger entry.  This allows context from the
+    event that exhibited the new maximum to be saved for later
+    reference.  When the histogram is displayed, additional fields
+    displaying the saved values will be printed.
+
+    As an example the below defines a couple of hist triggers, one for
+    sched_waking and another for sched_switch, keyed on pid.  Whenever
+    a sched_waking occurs, the timestamp is saved in the entry
+    corresponding to the current pid, and when the scheduler switches
+    back to that pid, the timestamp difference is calculated.  If the
+    resulting latency, stored in wakeup_lat, exceeds the current
+    maximum latency, the values specified in the save() fields are
+    recoreded:
+
+    # echo 'hist:keys=pid:ts0=$common_timestamp.usecs \
+            if comm=="cyclictest"' >> \
+            /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
+
+    # echo 'hist:keys=next_pid:\
+            wakeup_lat=$common_timestamp.usecs-$ts0:\
+            onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) \
+            if next_comm=="cyclictest"' >> \
+            /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
+
+    When the histogram is displayed, the max value and the saved
+    values corresponding to the max are displayed following the rest
+    of the fields:
+
+    # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist
+      { next_pid:       2255 } hitcount:        239
+        common_timestamp-ts0:          0
+        max:         27
+	next_comm: cyclictest
+        prev_pid:          0  prev_prio:        120  prev_comm: swapper/1
+
+      { next_pid:       2256 } hitcount:       2355
+        common_timestamp-ts0: 0
+        max:         49  next_comm: cyclictest
+        prev_pid:          0  prev_prio:        120  prev_comm: swapper/0
+
+      Totals:
+          Hits: 12970
+          Entries: 2
+          Dropped: 0
diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index bba2e5e6e917..4055f51617ef 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -116,8 +116,6 @@ void __jbd2_log_wait_for_space(journal_t *journal)
 	nblocks = jbd2_space_needed(journal);
 	while (jbd2_log_space_left(journal) < nblocks) {
 		write_unlock(&journal->j_state_lock);
-		if (current->plug)
-			io_schedule();
 		mutex_lock(&journal->j_checkpoint_mutex);
 
 		/*
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 96d16ddd6410..3bd606859b0a 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -110,6 +110,7 @@ enum hrtimer_restart {
  * @base:	pointer to the timer base (per cpu and per clock)
  * @state:	state information (See bit values above)
  * @is_rel:	Set if the timer was armed relative
+ * @is_soft:	Set if hrtimer will be expired in soft interrupt context.
  *
  * The hrtimer structure must be initialized by hrtimer_init()
  */
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index d76a47332502..e4f3246ea3a5 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -74,10 +74,6 @@ static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
 	raw_spin_unlock(&rt_b->rt_runtime_lock);
 }
 
-#if defined(CONFIG_SMP) && defined(HAVE_RT_PUSH_IPI)
-static void push_irq_work_func(struct irq_work *work);
-#endif
-
 void init_rt_rq(struct rt_rq *rt_rq)
 {
 	struct rt_prio_array *array;
@@ -97,14 +93,6 @@ void init_rt_rq(struct rt_rq *rt_rq)
 	rt_rq->rt_nr_migratory = 0;
 	rt_rq->overloaded = 0;
 	plist_head_init(&rt_rq->pushable_tasks);
-
-#ifdef HAVE_RT_PUSH_IPI
-	rt_rq->push_flags = 0;
-	rt_rq->push_cpu = nr_cpu_ids;
-	raw_spin_lock_init(&rt_rq->push_lock);
-	init_irq_work(&rt_rq->push_work, push_irq_work_func);
-	rt_rq->push_work.flags |= IRQ_WORK_HARD_IRQ;
-#endif
 #endif /* CONFIG_SMP */
 	/* We start is dequeued state, because no RT tasks are queued */
 	rt_rq->rt_queued = 0;
@@ -1877,68 +1865,6 @@ static void push_rt_tasks(struct rq *rq)
 }
 
 #ifdef HAVE_RT_PUSH_IPI
-/*
- * The search for the next cpu always starts at rq->cpu and ends
- * when we reach rq->cpu again. It will never return rq->cpu.
- * This returns the next cpu to check, or nr_cpu_ids if the loop
- * is complete.
- *
- * rq->rt.push_cpu holds the last cpu returned by this function,
- * or if this is the first instance, it must hold rq->cpu.
- */
-static int rto_next_cpu(struct rq *rq)
-{
-	int prev_cpu = rq->rt.push_cpu;
-	int cpu;
-
-	cpu = cpumask_next(prev_cpu, rq->rd->rto_mask);
-
-	/*
-	 * If the previous cpu is less than the rq's CPU, then it already
-	 * passed the end of the mask, and has started from the beginning.
-	 * We end if the next CPU is greater or equal to rq's CPU.
-	 */
-	if (prev_cpu < rq->cpu) {
-		if (cpu >= rq->cpu)
-			return nr_cpu_ids;
-
-	} else if (cpu >= nr_cpu_ids) {
-		/*
-		 * We passed the end of the mask, start at the beginning.
-		 * If the result is greater or equal to the rq's CPU, then
-		 * the loop is finished.
-		 */
-		cpu = cpumask_first(rq->rd->rto_mask);
-		if (cpu >= rq->cpu)
-			return nr_cpu_ids;
-	}
-	rq->rt.push_cpu = cpu;
-
-	/* Return cpu to let the caller know if the loop is finished or not */
-	return cpu;
-}
-
-static int find_next_push_cpu(struct rq *rq)
-{
-	struct rq *next_rq;
-	int cpu;
-
-	while (1) {
-		cpu = rto_next_cpu(rq);
-		if (cpu >= nr_cpu_ids)
-			break;
-		next_rq = cpu_rq(cpu);
-
-		/* Make sure the next rq can push to this rq */
-		if (next_rq->rt.highest_prio.next < rq->rt.highest_prio.curr)
-			break;
-	}
-
-	return cpu;
-}
-
-#define RT_PUSH_IPI_EXECUTING		1
-#define RT_PUSH_IPI_RESTART		2
 
 /*
  * When a high priority task schedules out from a CPU and a lower priority
@@ -1948,170 +1874,157 @@ static int find_next_push_cpu(struct rq *rq)
  * tasks queued on it (overloaded) needs to be notified that a CPU has opened
  * up that may be able to run one of its non-running queued RT tasks.
  *
- * On large CPU boxes, there's the case that several CPUs could schedule
- * a lower priority task at the same time, in which case it will look for
- * any overloaded CPUs that it could pull a task from. To do this, the runqueue
- * lock must be taken from that overloaded CPU. Having 10s of CPUs all fighting
- * for a single overloaded CPU's runqueue lock can produce a large latency.
- * (This has actually been observed on large boxes running cyclictest).
- * Instead of taking the runqueue lock of the overloaded CPU, each of the
- * CPUs that scheduled a lower priority task simply sends an IPI to the
- * overloaded CPU. An IPI is much cheaper than taking an runqueue lock with
- * lots of contention. The overloaded CPU will look to push its non-running
- * RT task off, and if it does, it can then ignore the other IPIs coming
- * in, and just pass those IPIs off to any other overloaded CPU.
+ * All CPUs with overloaded RT tasks need to be notified as there is currently
+ * no way to know which of these CPUs have the highest priority task waiting
+ * to run. Instead of trying to take a spinlock on each of these CPUs,
+ * which has shown to cause large latency when done on machines with many
+ * CPUs, sending an IPI to the CPUs to have them push off the overloaded
+ * RT tasks waiting to run.
  *
- * When a CPU schedules a lower priority task, it only sends an IPI to
- * the "next" CPU that has overloaded RT tasks. This prevents IPI storms,
- * as having 10 CPUs scheduling lower priority tasks and 10 CPUs with
- * RT overloaded tasks, would cause 100 IPIs to go out at once.
+ * Just sending an IPI to each of the CPUs is also an issue, as on large
+ * count CPU machines, this can cause an IPI storm on a CPU, especially
+ * if its the only CPU with multiple RT tasks queued, and a large number
+ * of CPUs scheduling a lower priority task at the same time.
  *
- * The overloaded RT CPU, when receiving an IPI, will try to push off its
- * overloaded RT tasks and then send an IPI to the next CPU that has
- * overloaded RT tasks. This stops when all CPUs with overloaded RT tasks
- * have completed. Just because a CPU may have pushed off its own overloaded
- * RT task does not mean it should stop sending the IPI around to other
- * overloaded CPUs. There may be another RT task waiting to run on one of
- * those CPUs that are of higher priority than the one that was just
- * pushed.
+ * Each root domain has its own irq work function that can iterate over
+ * all CPUs with RT overloaded tasks. Since all CPUs with overloaded RT
+ * tassk must be checked if there's one or many CPUs that are lowering
+ * their priority, there's a single irq work iterator that will try to
+ * push off RT tasks that are waiting to run.
  *
- * An optimization that could possibly be made is to make a CPU array similar
- * to the cpupri array mask of all running RT tasks, but for the overloaded
- * case, then the IPI could be sent to only the CPU with the highest priority
- * RT task waiting, and that CPU could send off further IPIs to the CPU with
- * the next highest waiting task. Since the overloaded case is much less likely
- * to happen, the complexity of this implementation may not be worth it.
- * Instead, just send an IPI around to all overloaded CPUs.
+ * When a CPU schedules a lower priority task, it will kick off the
+ * irq work iterator that will jump to each CPU with overloaded RT tasks.
+ * As it only takes the first CPU that schedules a lower priority task
+ * to start the process, the rto_start variable is incremented and if
+ * the atomic result is one, then that CPU will try to take the rto_lock.
+ * This prevents high contention on the lock as the process handles all
+ * CPUs scheduling lower priority tasks.
  *
- * The rq->rt.push_flags holds the status of the IPI that is going around.
- * A run queue can only send out a single IPI at a time. The possible flags
- * for rq->rt.push_flags are:
+ * All CPUs that are scheduling a lower priority task will increment the
+ * rt_loop_next variable. This will make sure that the irq work iterator
+ * checks all RT overloaded CPUs whenever a CPU schedules a new lower
+ * priority task, even if the iterator is in the middle of a scan. Incrementing
+ * the rt_loop_next will cause the iterator to perform another scan.
  *
- *    (None or zero):		No IPI is going around for the current rq
- *    RT_PUSH_IPI_EXECUTING:	An IPI for the rq is being passed around
- *    RT_PUSH_IPI_RESTART:	The priority of the running task for the rq
- *				has changed, and the IPI should restart
- *				circulating the overloaded CPUs again.
- *
- * rq->rt.push_cpu contains the CPU that is being sent the IPI. It is updated
- * before sending to the next CPU.
- *
- * Instead of having all CPUs that schedule a lower priority task send
- * an IPI to the same "first" CPU in the RT overload mask, they send it
- * to the next overloaded CPU after their own CPU. This helps distribute
- * the work when there's more than one overloaded CPU and multiple CPUs
- * scheduling in lower priority tasks.
- *
- * When a rq schedules a lower priority task than what was currently
- * running, the next CPU with overloaded RT tasks is examined first.
- * That is, if CPU 1 and 5 are overloaded, and CPU 3 schedules a lower
- * priority task, it will send an IPI first to CPU 5, then CPU 5 will
- * send to CPU 1 if it is still overloaded. CPU 1 will clear the
- * rq->rt.push_flags if RT_PUSH_IPI_RESTART is not set.
- *
- * The first CPU to notice IPI_RESTART is set, will clear that flag and then
- * send an IPI to the next overloaded CPU after the rq->cpu and not the next
- * CPU after push_cpu. That is, if CPU 1, 4 and 5 are overloaded when CPU 3
- * schedules a lower priority task, and the IPI_RESTART gets set while the
- * handling is being done on CPU 5, it will clear the flag and send it back to
- * CPU 4 instead of CPU 1.
- *
- * Note, the above logic can be disabled by turning off the sched_feature
- * RT_PUSH_IPI. Then the rq lock of the overloaded CPU will simply be
- * taken by the CPU requesting a pull and the waiting RT task will be pulled
- * by that CPU. This may be fine for machines with few CPUs.
  */
-static void tell_cpu_to_push(struct rq *rq)
+static int rto_next_cpu(struct rq *rq)
 {
+	struct root_domain *rd = rq->rd;
+	int next;
 	int cpu;
 
-	if (rq->rt.push_flags & RT_PUSH_IPI_EXECUTING) {
-		raw_spin_lock(&rq->rt.push_lock);
-		/* Make sure it's still executing */
-		if (rq->rt.push_flags & RT_PUSH_IPI_EXECUTING) {
-			/*
-			 * Tell the IPI to restart the loop as things have
-			 * changed since it started.
-			 */
-			rq->rt.push_flags |= RT_PUSH_IPI_RESTART;
-			raw_spin_unlock(&rq->rt.push_lock);
-			return;
-		}
-		raw_spin_unlock(&rq->rt.push_lock);
+	/*
+	 * When starting the IPI RT pushing, the rto_cpu is set to -1,
+	 * rt_next_cpu() will simply return the first CPU found in
+	 * the rto_mask.
+	 *
+	 * If rto_next_cpu() is called with rto_cpu is a valid cpu, it
+	 * will return the next CPU found in the rto_mask.
+	 *
+	 * If there are no more CPUs left in the rto_mask, then a check is made
+	 * against rto_loop and rto_loop_next. rto_loop is only updated with
+	 * the rto_lock held, but any CPU may increment the rto_loop_next
+	 * without any locking.
+	 */
+	for (;;) {
+
+		/* When rto_cpu is -1 this acts like cpumask_first() */
+		cpu = cpumask_next(rd->rto_cpu, rd->rto_mask);
+
+		rd->rto_cpu = cpu;
+
+		if (cpu < nr_cpu_ids)
+			return cpu;
+
+		rd->rto_cpu = -1;
+
+		/*
+		 * ACQUIRE ensures we see the @rto_mask changes
+		 * made prior to the @next value observed.
+		 *
+		 * Matches WMB in rt_set_overload().
+		 */
+		next = atomic_read_acquire(&rd->rto_loop_next);
+
+		if (rd->rto_loop == next)
+			break;
+
+		rd->rto_loop = next;
 	}
 
-	/* When here, there's no IPI going around */
+	return -1;
+}
 
-	rq->rt.push_cpu = rq->cpu;
-	cpu = find_next_push_cpu(rq);
-	if (cpu >= nr_cpu_ids)
+static inline bool rto_start_trylock(atomic_t *v)
+{
+	return !atomic_cmpxchg_acquire(v, 0, 1);
+}
+
+static inline void rto_start_unlock(atomic_t *v)
+{
+	atomic_set_release(v, 0);
+}
+
+static void tell_cpu_to_push(struct rq *rq)
+{
+	int cpu = -1;
+
+	/* Keep the loop going if the IPI is currently active */
+	atomic_inc(&rq->rd->rto_loop_next);
+
+	/* Only one CPU can initiate a loop at a time */
+	if (!rto_start_trylock(&rq->rd->rto_loop_start))
 		return;
 
-	rq->rt.push_flags = RT_PUSH_IPI_EXECUTING;
+	raw_spin_lock(&rq->rd->rto_lock);
 
-	irq_work_queue_on(&rq->rt.push_work, cpu);
+	/*
+	 * The rto_cpu is updated under the lock, if it has a valid cpu
+	 * then the IPI is still running and will continue due to the
+	 * update to loop_next, and nothing needs to be done here.
+	 * Otherwise it is finishing up and an ipi needs to be sent.
+	 */
+	if (rq->rd->rto_cpu < 0)
+		cpu = rto_next_cpu(rq);
+
+	raw_spin_unlock(&rq->rd->rto_lock);
+
+	rto_start_unlock(&rq->rd->rto_loop_start);
+
+	if (cpu >= 0)
+		irq_work_queue_on(&rq->rd->rto_push_work, cpu);
 }
 
 /* Called from hardirq context */
-static void try_to_push_tasks(void *arg)
+void rto_push_irq_work_func(struct irq_work *work)
 {
-	struct rt_rq *rt_rq = arg;
-	struct rq *rq, *src_rq;
-	int this_cpu;
+	struct rq *rq;
 	int cpu;
 
-	this_cpu = rt_rq->push_cpu;
+	rq = this_rq();
 
-	/* Paranoid check */
-	BUG_ON(this_cpu != smp_processor_id());
-
-	rq = cpu_rq(this_cpu);
-	src_rq = rq_of_rt_rq(rt_rq);
-
-again:
+	/*
+	 * We do not need to grab the lock to check for has_pushable_tasks.
+	 * When it gets updated, a check is made if a push is possible.
+	 */
 	if (has_pushable_tasks(rq)) {
 		raw_spin_lock(&rq->lock);
-		push_rt_task(rq);
+		push_rt_tasks(rq);
 		raw_spin_unlock(&rq->lock);
 	}
 
+	raw_spin_lock(&rq->rd->rto_lock);
+
 	/* Pass the IPI to the next rt overloaded queue */
-	raw_spin_lock(&rt_rq->push_lock);
-	/*
-	 * If the source queue changed since the IPI went out,
-	 * we need to restart the search from that CPU again.
-	 */
-	if (rt_rq->push_flags & RT_PUSH_IPI_RESTART) {
-		rt_rq->push_flags &= ~RT_PUSH_IPI_RESTART;
-		rt_rq->push_cpu = src_rq->cpu;
-	}
+	cpu = rto_next_cpu(rq);
 
-	cpu = find_next_push_cpu(src_rq);
+	raw_spin_unlock(&rq->rd->rto_lock);
 
-	if (cpu >= nr_cpu_ids)
-		rt_rq->push_flags &= ~RT_PUSH_IPI_EXECUTING;
-	raw_spin_unlock(&rt_rq->push_lock);
-
-	if (cpu >= nr_cpu_ids)
+	if (cpu < 0)
 		return;
 
-	/*
-	 * It is possible that a restart caused this CPU to be
-	 * chosen again. Don't bother with an IPI, just see if we
-	 * have more to push.
-	 */
-	if (unlikely(cpu == rq->cpu))
-		goto again;
-
 	/* Try the next RT overloaded CPU */
-	irq_work_queue_on(&rt_rq->push_work, cpu);
-}
-
-static void push_irq_work_func(struct irq_work *work)
-{
-	struct rt_rq *rt_rq = container_of(work, struct rt_rq, push_work);
-
-	try_to_push_tasks(rt_rq);
+	irq_work_queue_on(&rq->rd->rto_push_work, cpu);
 }
 #endif /* HAVE_RT_PUSH_IPI */
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index dbd5f0251e2f..220f10c3848b 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -502,7 +502,7 @@ static inline int rt_bandwidth_enabled(void)
 }
 
 /* RT IPI pull logic requires IRQ_WORK */
-#ifdef CONFIG_IRQ_WORK
+#if defined(CONFIG_IRQ_WORK) && defined(CONFIG_SMP)
 # define HAVE_RT_PUSH_IPI
 #endif
 
@@ -524,12 +524,6 @@ struct rt_rq {
 	unsigned long rt_nr_total;
 	int overloaded;
 	struct plist_head pushable_tasks;
-#ifdef HAVE_RT_PUSH_IPI
-	int push_flags;
-	int push_cpu;
-	struct irq_work push_work;
-	raw_spinlock_t push_lock;
-#endif
 #endif /* CONFIG_SMP */
 	int rt_queued;
 
@@ -638,6 +632,19 @@ struct root_domain {
 	struct dl_bw dl_bw;
 	struct cpudl cpudl;
 
+#ifdef HAVE_RT_PUSH_IPI
+	/*
+	 * For IPI pull requests, loop across the rto_mask.
+	 */
+	struct irq_work rto_push_work;
+	raw_spinlock_t rto_lock;
+	/* These are only updated and read within rto_lock */
+	int rto_loop;
+	int rto_cpu;
+	/* These atomics are updated outside of a lock */
+	atomic_t rto_loop_next;
+	atomic_t rto_loop_start;
+#endif
 	/*
 	 * The "RT overload" flag: it gets set if a CPU has more than
 	 * one runnable RT task.
@@ -655,6 +662,9 @@ extern void init_defrootdomain(void);
 extern int sched_init_domains(const struct cpumask *cpu_map);
 extern void rq_attach_root(struct rq *rq, struct root_domain *rd);
 
+#ifdef HAVE_RT_PUSH_IPI
+extern void rto_push_irq_work_func(struct irq_work *work);
+#endif
 #endif /* CONFIG_SMP */
 
 /*
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 6798276d29af..c88479dd4f5f 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -269,6 +269,13 @@ static int init_rootdomain(struct root_domain *rd)
 	if (!zalloc_cpumask_var(&rd->rto_mask, GFP_KERNEL))
 		goto free_dlo_mask;
 
+#ifdef HAVE_RT_PUSH_IPI
+	rd->rto_cpu = -1;
+	raw_spin_lock_init(&rd->rto_lock);
+	init_irq_work(&rd->rto_push_work, rto_push_irq_work_func);
+	rd->rto_push_work.flags |= IRQ_WORK_HARD_IRQ;
+#endif
+
 	init_dl_bw(&rd->dl_bw);
 	if (cpudl_init(&rd->cpudl) != 0)
 		goto free_rto_mask;
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index a48132182ed8..e277284c2831 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -151,11 +151,10 @@ static inline void tick_nohz_init(void) { }
 #ifdef CONFIG_NO_HZ_COMMON
 extern unsigned long tick_nohz_active;
 extern void timers_update_nohz(void);
-
-#ifdef CONFIG_SMP
+# ifdef CONFIG_SMP
 extern struct static_key_false timers_migration_enabled;
-#endif
-#else
+# endif
+#else /* CONFIG_NO_HZ_COMMON */
 static inline void timers_update_nohz(void) { }
 #define tick_nohz_active (0)
 #endif
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index a116521f2d99..40ac38728b7a 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -276,14 +276,8 @@ static inline bool is_timers_nohz_active(void)
 {
 	return static_branch_unlikely(&timers_nohz_active);
 }
-
 #else
-
-static inline bool is_timers_nohz_active(void)
-{
-	return false;
-}
-
+static inline bool is_timers_nohz_active(void) { return false; }
 #endif /* NO_HZ_COMMON */
 
 static unsigned long round_jiffies_common(unsigned long j, int cpu,
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index f78a1ad89f82..8c862ea52171 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2246,7 +2246,7 @@ rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
 }
 
 /* Slow path, do not inline */
-static struct noinline ring_buffer_event *
+static noinline struct ring_buffer_event *
 rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
 {
 	if (abs)
@@ -2519,10 +2519,6 @@ rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
 {
 	u64 delta;
 
-	/* In TIME_STAMP mode, write_stamp is unused, nothing to do */
-	if (event->type_len == RINGBUF_TYPE_TIME_STAMP)
-		return;
-
 	/*
 	 * The event first in the commit queue updates the
 	 * time stamp.
@@ -2538,6 +2534,9 @@ rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
 		else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
 			delta = ring_buffer_event_time_stamp(event);
 			cpu_buffer->write_stamp += delta;
+		} else if (event->type_len == RINGBUF_TYPE_TIME_STAMP) {
+			delta = ring_buffer_event_time_stamp(event);
+			cpu_buffer->write_stamp = delta;
 		} else
 			cpu_buffer->write_stamp += event->time_delta;
 	}
@@ -3459,7 +3458,8 @@ rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
 		return;
 
 	case RINGBUF_TYPE_TIME_STAMP:
-		/* In TIME_STAMP mode, write_stamp is unused, nothing to do */
+		delta = ring_buffer_event_time_stamp(event);
+		cpu_buffer->read_stamp = delta;
 		return;
 
 	case RINGBUF_TYPE_DATA:
@@ -3488,7 +3488,8 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
 		return;
 
 	case RINGBUF_TYPE_TIME_STAMP:
-		/* In TIME_STAMP mode, write_stamp is unused, nothing to do */
+		delta = ring_buffer_event_time_stamp(event);
+		iter->read_stamp = delta;
 		return;
 
 	case RINGBUF_TYPE_DATA:
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a0240cf373a2..2ff4998b50dd 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4548,6 +4548,9 @@ static const char readme_msg[] =
 #ifdef CONFIG_X86_64
 	"     x86-tsc:   TSC cycle counter\n"
 #endif
+	"\n  timestamp_mode\t-view the mode used to timestamp events\n"
+	"       delta:   Delta difference against a buffer-wide timestamp\n"
+	"    absolute:   Absolute (standalone) timestamp\n"
 	"\n  trace_marker\t\t- Writes into this file writes into the kernel buffer\n"
 	"\n  trace_marker_raw\t\t- Writes into this file writes binary data into the kernel buffer\n"
 	"  tracing_cpumask\t- Limit which CPUs to trace\n"
@@ -4724,8 +4727,9 @@ static const char readme_msg[] =
 	"\t            .sym        display an address as a symbol\n"
 	"\t            .sym-offset display an address as a symbol and offset\n"
 	"\t            .execname   display a common_pid as a program name\n"
-	"\t            .syscall    display a syscall id as a syscall name\n\n"
-	"\t            .log2       display log2 value rather than raw number\n\n"
+	"\t            .syscall    display a syscall id as a syscall name\n"
+	"\t            .log2       display log2 value rather than raw number\n"
+	"\t            .usecs      display a $common_timestamp in microseconds\n\n"
 	"\t    The 'pause' parameter can be used to pause an existing hist\n"
 	"\t    trigger or to start a hist trigger but not log any events\n"
 	"\t    until told to do so.  'continue' can be used to start or\n"
@@ -6315,6 +6319,40 @@ static int tracing_clock_open(struct inode *inode, struct file *file)
 	return ret;
 }
 
+static int tracing_time_stamp_mode_show(struct seq_file *m, void *v)
+{
+	struct trace_array *tr = m->private;
+
+	mutex_lock(&trace_types_lock);
+
+	if (ring_buffer_time_stamp_abs(tr->trace_buffer.buffer))
+		seq_puts(m, "delta [absolute]\n");
+	else
+		seq_puts(m, "[delta] absolute\n");
+
+	mutex_unlock(&trace_types_lock);
+
+	return 0;
+}
+
+static int tracing_time_stamp_mode_open(struct inode *inode, struct file *file)
+{
+	struct trace_array *tr = inode->i_private;
+	int ret;
+
+	if (tracing_disabled)
+		return -ENODEV;
+
+	if (trace_array_get(tr))
+		return -ENODEV;
+
+	ret = single_open(file, tracing_time_stamp_mode_show, inode->i_private);
+	if (ret < 0)
+		trace_array_put(tr);
+
+	return ret;
+}
+
 int tracing_set_time_stamp_abs(struct trace_array *tr, bool abs)
 {
 	int ret = 0;
@@ -6336,16 +6374,9 @@ int tracing_set_time_stamp_abs(struct trace_array *tr, bool abs)
 
 	ring_buffer_set_time_stamp_abs(tr->trace_buffer.buffer, abs);
 
-	/*
-	 * New timestamps may not be consistent with the previous setting.
-	 * Reset the buffer so that it doesn't have incomparable timestamps.
-	 */
-	tracing_reset_online_cpus(&tr->trace_buffer);
-
 #ifdef CONFIG_TRACER_MAX_TRACE
 	if (tr->max_buffer.buffer)
 		ring_buffer_set_time_stamp_abs(tr->max_buffer.buffer, abs);
-	tracing_reset_online_cpus(&tr->max_buffer);
 #endif
  out:
 	mutex_unlock(&trace_types_lock);
@@ -6600,6 +6631,13 @@ static const struct file_operations trace_clock_fops = {
 	.write		= tracing_clock_write,
 };
 
+static const struct file_operations trace_time_stamp_mode_fops = {
+	.open		= tracing_time_stamp_mode_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= tracing_single_release_tr,
+};
+
 #ifdef CONFIG_TRACER_SNAPSHOT
 static const struct file_operations snapshot_fops = {
 	.open		= tracing_snapshot_open,
@@ -7928,6 +7966,9 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
 	trace_create_file("tracing_on", 0644, d_tracer,
 			  tr, &rb_simple_fops);
 
+	trace_create_file("timestamp_mode", 0444, d_tracer, tr,
+			  &trace_time_stamp_mode_fops);
+
 	create_trace_options_dir(tr);
 
 #if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index e884d5d78551..eb821cd223b1 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -66,6 +66,8 @@ struct hist_field {
 	struct hist_trigger_data	*hist_data;
 	struct hist_var			var;
 	enum field_op_id		operator;
+	char				*system;
+	char				*event_name;
 	char				*name;
 	unsigned int			var_idx;
 	unsigned int			var_ref_idx;
@@ -223,11 +225,10 @@ enum hist_field_flags {
 	HIST_FIELD_FL_TIMESTAMP		= 1 << 10,
 	HIST_FIELD_FL_TIMESTAMP_USECS	= 1 << 11,
 	HIST_FIELD_FL_VAR		= 1 << 12,
-	HIST_FIELD_FL_VAR_ONLY		= 1 << 13,
-	HIST_FIELD_FL_EXPR		= 1 << 14,
-	HIST_FIELD_FL_VAR_REF		= 1 << 15,
-	HIST_FIELD_FL_CPU		= 1 << 16,
-	HIST_FIELD_FL_ALIAS		= 1 << 17,
+	HIST_FIELD_FL_EXPR		= 1 << 13,
+	HIST_FIELD_FL_VAR_REF		= 1 << 14,
+	HIST_FIELD_FL_CPU		= 1 << 15,
+	HIST_FIELD_FL_ALIAS		= 1 << 16,
 };
 
 struct var_defs {
@@ -273,7 +274,6 @@ struct hist_trigger_data {
 	unsigned int			n_keys;
 	unsigned int			n_fields;
 	unsigned int			n_vars;
-	unsigned int			n_var_only;
 	unsigned int			key_size;
 	struct tracing_map_sort_key	sort_keys[TRACING_MAP_SORT_KEYS_MAX];
 	unsigned int			n_sort_keys;
@@ -575,7 +575,7 @@ static const char *synth_field_fmt(char *type)
 		fmt = "%lu";
 	else if (strcmp(type, "pid_t") == 0)
 		fmt = "%d";
-	else if (strstr(type, "[") == 0)
+	else if (strchr(type, '[') != NULL)
 		fmt = "%s";
 
 	return fmt;
@@ -859,7 +859,6 @@ static struct synth_event *find_synth_event(const char *name)
 	return NULL;
 }
 
-/* This function releases synth_event_mutex */
 static int register_synth_event(struct synth_event *event)
 {
 	struct trace_event_call *call = &event->call;
@@ -894,14 +893,7 @@ static int register_synth_event(struct synth_event *event)
 	call->data = event;
 	call->tp = event->tp;
 
-	/*
-	 * trace_add_event_call() grabs event_mutex, but that can
-	 * deadlock with a hist trigger cmd already holding it that
-	 * can grab synth_event_mutex
-	 */
-	mutex_unlock(&synth_event_mutex);
 	ret = trace_add_event_call(call);
-	mutex_lock(&synth_event_mutex);
 	if (ret) {
 		pr_warn("Failed to register synthetic event: %s\n",
 			trace_event_name(call));
@@ -910,9 +902,7 @@ static int register_synth_event(struct synth_event *event)
 
 	ret = set_synth_event_print_fmt(call);
 	if (ret < 0) {
-		mutex_unlock(&synth_event_mutex);
 		trace_remove_event_call(call);
-		mutex_lock(&synth_event_mutex);
 		goto err;
 	}
  out:
@@ -922,42 +912,16 @@ static int register_synth_event(struct synth_event *event)
 	goto out;
 }
 
-/* This function releases synth_event_mutex */
 static int unregister_synth_event(struct synth_event *event)
 {
 	struct trace_event_call *call = &event->call;
 	int ret;
 
-	mutex_unlock(&synth_event_mutex);
 	ret = trace_remove_event_call(call);
-	mutex_lock(&synth_event_mutex);
 
 	return ret;
 }
 
-static int remove_synth_event(struct synth_event *event)
-{
-	int ret = unregister_synth_event(event);
-
-	if (!ret)
-		list_del(&event->list);
-
-	return ret;
-}
-
-static int add_synth_event(struct synth_event *event)
-{
-	int ret;
-
-	ret = register_synth_event(event);
-	if (ret)
-		return ret;
-
-	list_add(&event->list, &synth_event_list);
-
-	return 0;
-}
-
 static void free_synth_event(struct synth_event *event)
 {
 	unsigned int i;
@@ -995,7 +959,7 @@ static struct synth_event *alloc_synth_event(char *event_name, int n_fields,
 		goto out;
 	}
 
-	event->fields = kcalloc(n_fields, sizeof(event->fields), GFP_KERNEL);
+	event->fields = kcalloc(n_fields, sizeof(*event->fields), GFP_KERNEL);
 	if (!event->fields) {
 		free_synth_event(event);
 		event = ERR_PTR(-ENOMEM);
@@ -1025,7 +989,6 @@ struct hist_var_data {
 	struct hist_trigger_data *hist_data;
 };
 
-/* This function releases synth_event_mutex */
 static int create_synth_event(int argc, char **argv)
 {
 	struct synth_field *field, *fields[SYNTH_FIELDS_MAX];
@@ -1057,14 +1020,14 @@ static int create_synth_event(int argc, char **argv)
 	if (event) {
 		if (delete_event) {
 			if (event->ref) {
+				event = NULL;
 				ret = -EBUSY;
 				goto out;
 			}
-			ret = remove_synth_event(event);
-			if (!ret)
-				free_synth_event(event);
+			list_del(&event->list);
 			goto out;
 		}
+		event = NULL;
 		ret = -EEXIST;
 		goto out;
 	} else if (delete_event)
@@ -1103,43 +1066,85 @@ static int create_synth_event(int argc, char **argv)
 		event = NULL;
 		goto err;
 	}
-
-	add_synth_event(event);
  out:
 	mutex_unlock(&synth_event_mutex);
 
+	if (event) {
+		if (delete_event) {
+			ret = unregister_synth_event(event);
+			if (!ret)
+				free_synth_event(event);
+			else {
+				mutex_lock(&synth_event_mutex);
+				if (!find_synth_event(event->name))
+					list_add(&event->list, &synth_event_list);
+				mutex_unlock(&synth_event_mutex);
+			}
+		} else {
+			ret = register_synth_event(event);
+			if (!ret) {
+				mutex_lock(&synth_event_mutex);
+				if (!find_synth_event(event->name))
+					list_add(&event->list, &synth_event_list);
+				mutex_unlock(&synth_event_mutex);
+			} else
+				free_synth_event(event);
+		}
+	}
+
 	return ret;
  err:
+	mutex_unlock(&synth_event_mutex);
+
 	for (i = 0; i < n_fields; i++)
 		free_synth_field(fields[i]);
 	free_synth_event(event);
 
-	goto out;
+	return ret;
 }
 
-/* This function releases synth_event_mutex */
 static int release_all_synth_events(void)
 {
+	struct list_head release_events;
 	struct synth_event *event, *e;
-	int ret = 0;
+	int ret = 0, err = 0;
+
+	INIT_LIST_HEAD(&release_events);
 
 	mutex_lock(&synth_event_mutex);
 
 	list_for_each_entry(event, &synth_event_list, list) {
 		if (event->ref) {
-			ret = -EBUSY;
-			goto out;
+			mutex_unlock(&synth_event_mutex);
+			return -EBUSY;
 		}
 	}
 
 	list_for_each_entry_safe(event, e, &synth_event_list, list) {
-		ret = remove_synth_event(event);
-		if (!ret)
-			free_synth_event(event);
+		list_del(&event->list);
+		list_add(&event->list, &release_events);
 	}
- out:
+
 	mutex_unlock(&synth_event_mutex);
 
+	list_for_each_entry_safe(event, e, &release_events, list) {
+		list_del(&event->list);
+
+		ret = unregister_synth_event(event);
+		if (ret == 0)
+			free_synth_event(event);
+		else {
+			err = ret;
+			mutex_lock(&synth_event_mutex);
+			if (!find_synth_event(event->name))
+				list_add(&event->list, &synth_event_list);
+			mutex_unlock(&synth_event_mutex);
+		}
+	}
+
+	if (err)
+		ret = err;
+
 	return ret;
 }
 
@@ -1244,9 +1249,10 @@ static u64 hist_field_cpu(struct hist_field *hist_field,
 	return cpu;
 }
 
-static struct hist_field *check_var_ref(struct hist_field *hist_field,
-					struct hist_trigger_data *var_data,
-					unsigned int var_idx)
+static struct hist_field *
+check_field_for_var_ref(struct hist_field *hist_field,
+			struct hist_trigger_data *var_data,
+			unsigned int var_idx)
 {
 	struct hist_field *found = NULL;
 
@@ -1260,27 +1266,52 @@ static struct hist_field *check_var_ref(struct hist_field *hist_field,
 	return found;
 }
 
+static struct hist_field *
+check_field_for_var_refs(struct hist_trigger_data *hist_data,
+			 struct hist_field *hist_field,
+			 struct hist_trigger_data *var_data,
+			 unsigned int var_idx,
+			 unsigned int level)
+{
+	struct hist_field *found = NULL;
+	unsigned int i;
+
+	if (level > 2)
+		return found;
+
+	if (!hist_field)
+		return found;
+
+	found = check_field_for_var_ref(hist_field, var_data, var_idx);
+	if (found)
+		return found;
+
+	for (i = 0; i < HIST_FIELD_OPERANDS_MAX; i++) {
+		struct hist_field *operand;
+
+		operand = hist_field->operands[i];
+		found = check_field_for_var_refs(hist_data, operand, var_data,
+						 var_idx, level + 1);
+		if (found)
+			return found;
+	}
+
+	return found;
+}
+
 static struct hist_field *find_var_ref(struct hist_trigger_data *hist_data,
 				       struct hist_trigger_data *var_data,
 				       unsigned int var_idx)
 {
 	struct hist_field *hist_field, *found = NULL;
-	unsigned int i, j;
+	unsigned int i;
 
 	for_each_hist_field(i, hist_data) {
 		hist_field = hist_data->fields[i];
-		found = check_var_ref(hist_field, var_data, var_idx);
+		found = check_field_for_var_refs(hist_data, hist_field,
+						 var_data, var_idx, 0);
 		if (found)
 			return found;
-
-		for (j = 0; j < HIST_FIELD_OPERANDS_MAX; j++) {
-			struct hist_field *operand;
-
-			operand = hist_field->operands[j];
-			found = check_var_ref(operand, var_data, var_idx);
-			if (found)
-				return found;
-		}
 	}
 
 	return found;
@@ -1293,6 +1324,10 @@ static struct hist_field *find_any_var_ref(struct hist_trigger_data *hist_data,
 	struct hist_field *found = NULL;
 	struct hist_var_data *var_data;
 
+	found = find_var_ref(hist_data, hist_data, var_idx);
+	if (found)
+		return found;
+
 	list_for_each_entry(var_data, &tr->hist_vars, list) {
 		found = find_var_ref(var_data->hist_data, hist_data, var_idx);
 		if (found)
@@ -1336,27 +1371,41 @@ static struct hist_var_data *find_hist_vars(struct hist_trigger_data *hist_data)
 	return found;
 }
 
+static bool field_has_hist_vars(struct hist_field *hist_field,
+				unsigned int level)
+{
+	int i;
+
+	if (level > 2)
+		return false;
+
+	if (!hist_field)
+		return false;
+
+	if (hist_field->flags & HIST_FIELD_FL_VAR ||
+	    hist_field->flags & HIST_FIELD_FL_VAR_REF)
+		return true;
+
+	for (i = 0; i < HIST_FIELD_OPERANDS_MAX; i++) {
+		struct hist_field *operand;
+
+		operand = hist_field->operands[i];
+		if (field_has_hist_vars(operand, level + 1))
+			return true;
+	}
+
+	return false;
+}
+
 static bool has_hist_vars(struct hist_trigger_data *hist_data)
 {
 	struct hist_field *hist_field;
-	int i, j;
+	int i;
 
 	for_each_hist_field(i, hist_data) {
 		hist_field = hist_data->fields[i];
-		if (hist_field &&
-		    (hist_field->flags & HIST_FIELD_FL_VAR ||
-		     hist_field->flags & HIST_FIELD_FL_VAR_REF))
+		if (field_has_hist_vars(hist_field, 0))
 			return true;
-
-		for (j = 0; j < HIST_FIELD_OPERANDS_MAX; j++) {
-			struct hist_field *operand;
-
-			operand = hist_field->operands[j];
-			if (operand &&
-			    (operand->flags & HIST_FIELD_FL_VAR ||
-			     operand->flags & HIST_FIELD_FL_VAR_REF))
-				return true;
-		}
 	}
 
 	return false;
@@ -1423,17 +1472,22 @@ static struct hist_field *find_var_field(struct hist_trigger_data *hist_data,
 	return found;
 }
 
-static struct hist_field *find_var(struct trace_event_file *file,
+static struct hist_field *find_var(struct hist_trigger_data *hist_data,
+				   struct trace_event_file *file,
 				   const char *var_name)
 {
-	struct hist_trigger_data *hist_data;
+	struct hist_trigger_data *test_data;
 	struct event_trigger_data *test;
 	struct hist_field *hist_field;
 
+	hist_field = find_var_field(hist_data, var_name);
+	if (hist_field)
+		return hist_field;
+
 	list_for_each_entry_rcu(test, &file->triggers, list) {
 		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
-			hist_data = test->private_data;
-			hist_field = find_var_field(hist_data, var_name);
+			test_data = test->private_data;
+			hist_field = find_var_field(test_data, var_name);
 			if (hist_field)
 				return hist_field;
 		}
@@ -1443,25 +1497,33 @@ static struct hist_field *find_var(struct trace_event_file *file,
 }
 
 static struct trace_event_file *find_var_file(struct trace_array *tr,
-					      const char *system,
-					      const char *event_name,
-					      const char *var_name)
+					      char *system,
+					      char *event_name,
+					      char *var_name)
 {
 	struct hist_trigger_data *var_hist_data;
 	struct hist_var_data *var_data;
 	struct trace_event_call *call;
-	struct trace_event_file *file;
+	struct trace_event_file *file, *found = NULL;
 	const char *name;
 
 	list_for_each_entry(var_data, &tr->hist_vars, list) {
 		var_hist_data = var_data->hist_data;
 		file = var_hist_data->event_file;
+		if (file == found)
+			continue;
 		call = file->event_call;
 		name = trace_event_name(call);
 
 		if (!system || !event_name) {
-			if (find_var(file, var_name))
-				return file;
+			if (find_var(var_hist_data, file, var_name)) {
+				if (found) {
+					hist_err_event("Variable name not unique, need to use fully qualified name (subsys.event.var) for variable: ", system, event_name, var_name);
+					return NULL;
+				}
+
+				found = file;
+			}
 			continue;
 		}
 
@@ -1470,10 +1532,11 @@ static struct trace_event_file *find_var_file(struct trace_array *tr,
 		if (strcmp(system, call->class->system) != 0)
 			continue;
 
-		return file;
+		found = file;
+		break;
 	}
 
-	return NULL;
+	return found;
 }
 
 static struct hist_field *find_file_var(struct trace_event_file *file,
@@ -1495,14 +1558,55 @@ static struct hist_field *find_file_var(struct trace_event_file *file,
 	return NULL;
 }
 
-static struct hist_field *find_event_var(struct trace_array *tr,
-					 const char *system,
-					 const char *event_name,
-					 const char *var_name)
+static struct hist_field *
+find_match_var(struct hist_trigger_data *hist_data, char *var_name)
 {
+	struct trace_array *tr = hist_data->event_file->tr;
+	struct hist_field *hist_field, *found = NULL;
+	struct trace_event_file *file;
+	unsigned int i;
+
+	for (i = 0; i < hist_data->n_actions; i++) {
+		struct action_data *data = hist_data->actions[i];
+
+		if (data->fn == action_trace) {
+			char *system = data->onmatch.match_event_system;
+			char *event_name = data->onmatch.match_event;
+
+			file = find_var_file(tr, system, event_name, var_name);
+			if (!file)
+				continue;
+			hist_field = find_file_var(file, var_name);
+			if (hist_field) {
+				if (found) {
+					hist_err_event("Variable name not unique, need to use fully qualified name (subsys.event.var) for variable: ", system, event_name, var_name);
+					return ERR_PTR(-EINVAL);
+				}
+
+				found = hist_field;
+			}
+		}
+	}
+	return found;
+}
+
+static struct hist_field *find_event_var(struct hist_trigger_data *hist_data,
+					 char *system,
+					 char *event_name,
+					 char *var_name)
+{
+	struct trace_array *tr = hist_data->event_file->tr;
 	struct hist_field *hist_field = NULL;
 	struct trace_event_file *file;
 
+	if (!system || !event_name) {
+		hist_field = find_match_var(hist_data, var_name);
+		if (IS_ERR(hist_field))
+			return NULL;
+		if (hist_field)
+			return hist_field;
+	}
+
 	file = find_var_file(tr, system, event_name, var_name);
 	if (!file)
 		return NULL;
@@ -1596,8 +1700,19 @@ static const char *hist_field_name(struct hist_field *field,
 	else if (field->flags & HIST_FIELD_FL_CPU)
 		field_name = "cpu";
 	else if (field->flags & HIST_FIELD_FL_EXPR ||
-		 field->flags & HIST_FIELD_FL_VAR_REF)
-		field_name = field->name;
+		 field->flags & HIST_FIELD_FL_VAR_REF) {
+		if (field->system) {
+			static char full_name[MAX_FILTER_STR_VAL];
+
+			strcat(full_name, field->system);
+			strcat(full_name, ".");
+			strcat(full_name, field->event_name);
+			strcat(full_name, ".");
+			strcat(full_name, field->name);
+			field_name = full_name;
+		} else
+			field_name = field->name;
+	}
 
 	if (field_name == NULL)
 		field_name = "";
@@ -1762,6 +1877,7 @@ static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
 		char *assignment;
 
 		if (attrs->n_assignments == TRACING_MAP_VARS_MAX) {
+			hist_err("Too many variables defined: ", str);
 			ret = -EINVAL;
 			goto out;
 		}
@@ -2178,34 +2294,60 @@ static void destroy_hist_fields(struct hist_trigger_data *hist_data)
 }
 
 static int init_var_ref(struct hist_field *ref_field,
-			struct hist_field *var_field)
+			struct hist_field *var_field,
+			char *system, char *event_name)
 {
+	int err = 0;
+
 	ref_field->var.idx = var_field->var.idx;
 	ref_field->var.hist_data = var_field->hist_data;
 	ref_field->size = var_field->size;
 	ref_field->is_signed = var_field->is_signed;
 
+	if (system) {
+		ref_field->system = kstrdup(system, GFP_KERNEL);
+		if (!ref_field->system)
+			return -ENOMEM;
+	}
+
+	if (event_name) {
+		ref_field->event_name = kstrdup(event_name, GFP_KERNEL);
+		if (!ref_field->event_name) {
+			err = -ENOMEM;
+			goto free;
+		}
+	}
+
 	ref_field->name = kstrdup(var_field->var.name, GFP_KERNEL);
-	if (!ref_field->name)
-		return -ENOMEM;
+	if (!ref_field->name) {
+		err = -ENOMEM;
+		goto free;
+	}
 
 	ref_field->type = kstrdup(var_field->type, GFP_KERNEL);
 	if (!ref_field->type) {
-		kfree(ref_field->name);
-		return -ENOMEM;
+		err = -ENOMEM;
+		goto free;
 	}
+ out:
+	return err;
+ free:
+	kfree(ref_field->system);
+	kfree(ref_field->event_name);
+	kfree(ref_field->name);
 
-	return 0;
+	goto out;
 }
 
-static struct hist_field *create_var_ref(struct hist_field *var_field)
+static struct hist_field *create_var_ref(struct hist_field *var_field,
+					 char *system, char *event_name)
 {
 	unsigned long flags = HIST_FIELD_FL_VAR_REF;
 	struct hist_field *ref_field;
 
 	ref_field = create_hist_field(var_field->hist_data, NULL, flags, NULL);
 	if (ref_field) {
-		if (init_var_ref(ref_field, var_field)) {
+		if (init_var_ref(ref_field, var_field, system, event_name)) {
 			destroy_hist_field(ref_field, 0);
 			return NULL;
 		}
@@ -2262,7 +2404,7 @@ static char *local_field_var_ref(struct hist_trigger_data *hist_data,
 	return field_name_from_var(hist_data, var_name);
 }
 
-static struct hist_field *parse_var_ref(struct trace_array *tr,
+static struct hist_field *parse_var_ref(struct hist_trigger_data *hist_data,
 					char *system, char *event_name,
 					char *var_name)
 {
@@ -2273,9 +2415,9 @@ static struct hist_field *parse_var_ref(struct trace_array *tr,
 
 	var_name++;
 
-	var_field = find_event_var(tr, system, event_name, var_name);
+	var_field = find_event_var(hist_data, system, event_name, var_name);
 	if (var_field)
-		ref_field = create_var_ref(var_field);
+		ref_field = create_var_ref(var_field, system, event_name);
 
 	if (!ref_field)
 		hist_err_event("Couldn't find variable: $",
@@ -2343,8 +2485,7 @@ static struct hist_field *create_alias(struct hist_trigger_data *hist_data,
 				       char *var_name)
 {
 	struct hist_field *alias = NULL;
-	unsigned long flags = HIST_FIELD_FL_ALIAS | HIST_FIELD_FL_VAR |
-		HIST_FIELD_FL_VAR_ONLY;
+	unsigned long flags = HIST_FIELD_FL_ALIAS | HIST_FIELD_FL_VAR;
 
 	alias = create_hist_field(hist_data, NULL, flags, var_name);
 	if (!alias)
@@ -2353,7 +2494,7 @@ static struct hist_field *create_alias(struct hist_trigger_data *hist_data,
 	alias->fn = var_ref->fn;
 	alias->operands[0] = var_ref;
 
-	if (init_var_ref(alias, var_ref)) {
+	if (init_var_ref(alias, var_ref, var_ref->system, var_ref->event_name)) {
 		destroy_hist_field(alias, 0);
 		return NULL;
 	}
@@ -2366,7 +2507,6 @@ struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
 			      unsigned long *flags, char *var_name)
 {
 	char *s, *ref_system = NULL, *ref_event = NULL, *ref_var = str;
-	struct trace_array *tr = hist_data->event_file->tr;
 	struct ftrace_event_field *field = NULL;
 	struct hist_field *hist_field = NULL;
 	int ret = 0;
@@ -2391,7 +2531,7 @@ struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
 
 	s = local_field_var_ref(hist_data, ref_var);
 	if (!s) {
-		hist_field = parse_var_ref(tr, ref_system, ref_event, ref_var);
+		hist_field = parse_var_ref(hist_data, ref_system, ref_event, ref_var);
 		if (hist_field) {
 			hist_data->var_refs[hist_data->n_var_refs] = hist_field;
 			hist_field->var_ref_idx = hist_data->n_var_refs++;
@@ -2496,6 +2636,7 @@ static struct hist_field *parse_unary(struct hist_trigger_data *hist_data,
 
 	return expr;
  free:
+	destroy_hist_field(expr, 0);
 	return ERR_PTR(ret);
 }
 
@@ -2714,9 +2855,55 @@ static struct trace_event_file *event_file(struct trace_array *tr,
 	return file;
 }
 
+static struct hist_field *
+find_synthetic_field_var(struct hist_trigger_data *target_hist_data,
+			 char *system, char *event_name, char *field_name)
+{
+	struct hist_field *event_var;
+	char *synthetic_name;
+
+	synthetic_name = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
+	if (!synthetic_name)
+		return ERR_PTR(-ENOMEM);
+
+	strcpy(synthetic_name, "synthetic_");
+	strcat(synthetic_name, field_name);
+
+	event_var = find_event_var(target_hist_data, system, event_name, synthetic_name);
+
+	kfree(synthetic_name);
+
+	return event_var;
+}
+
+/**
+ * create_field_var_hist - Automatically create a histogram and var for a field
+ * @target_hist_data: The target hist trigger
+ * @subsys_name: Optional subsystem name
+ * @event_name: Optional event name
+ * @field_name: The name of the field (and the resulting variable)
+ *
+ * Hist trigger actions fetch data from variables, not directly from
+ * events.  However, for convenience, users are allowed to directly
+ * specify an event field in an action, which will be automatically
+ * converted into a variable on their behalf.
+
+ * If a user specifies a field on an event that isn't the event the
+ * histogram currently being defined (the target event histogram), the
+ * only way that can be accomplished is if a new hist trigger is
+ * created and the field variable defined on that.
+ *
+ * This function creates a new histogram compatible with the target
+ * event (meaning a histogram with the same key as the target
+ * histogram), and creates a variable for the specified field, but
+ * with 'synthetic_' prepended to the variable name in order to avoid
+ * collision with normal field variables.
+ *
+ * Return: The variable created for the field.
+ */
 static struct hist_field *
 create_field_var_hist(struct hist_trigger_data *target_hist_data,
-		      char *system, char *event_name, char *field_name)
+		      char *subsys_name, char *event_name, char *field_name)
 {
 	struct trace_array *tr = target_hist_data->event_file->tr;
 	struct hist_field *event_var = ERR_PTR(-EINVAL);
@@ -2731,26 +2918,38 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
 
 	if (target_hist_data->n_field_var_hists >= SYNTH_FIELDS_MAX) {
 		hist_err_event("onmatch: Too many field variables defined: ",
-			       system, event_name, field_name);
+			       subsys_name, event_name, field_name);
 		return ERR_PTR(-EINVAL);
 	}
 
-	file = event_file(tr, system, event_name);
+	file = event_file(tr, subsys_name, event_name);
 
 	if (IS_ERR(file)) {
 		hist_err_event("onmatch: Event file not found: ",
-			       system, event_name, field_name);
+			       subsys_name, event_name, field_name);
 		ret = PTR_ERR(file);
 		return ERR_PTR(ret);
 	}
 
+	/*
+	 * Look for a histogram compatible with target.  We'll use the
+	 * found histogram specification to create a new matching
+	 * histogram with our variable on it.  target_hist_data is not
+	 * yet a registered histogram so we can't use that.
+	 */
 	hist_data = find_compatible_hist(target_hist_data, file);
 	if (!hist_data) {
 		hist_err_event("onmatch: Matching event histogram not found: ",
-			       system, event_name, field_name);
+			       subsys_name, event_name, field_name);
 		return ERR_PTR(-EINVAL);
 	}
 
+	/* See if a synthetic field variable has already been created */
+	event_var = find_synthetic_field_var(target_hist_data, subsys_name,
+					     event_name, field_name);
+	if (event_var && !IS_ERR(event_var))
+		return event_var;
+
 	var_hist = kzalloc(sizeof(*var_hist), GFP_KERNEL);
 	if (!var_hist)
 		return ERR_PTR(-ENOMEM);
@@ -2761,6 +2960,7 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
 		return ERR_PTR(-ENOMEM);
 	}
 
+	/* Use the same keys as the compatible histogram */
 	strcat(cmd, "keys=");
 
 	for_each_hist_key_field(i, hist_data) {
@@ -2771,11 +2971,13 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
 		first = false;
 	}
 
+	/* Create the synthetic field variable specification */
 	strcat(cmd, ":synthetic_");
 	strcat(cmd, field_name);
 	strcat(cmd, "=");
 	strcat(cmd, field_name);
 
+	/* Use the same filter as the compatible histogram */
 	saved_filter = find_trigger_filter(hist_data, file);
 	if (saved_filter) {
 		strcat(cmd, " if ");
@@ -2789,8 +2991,10 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
 		return ERR_PTR(-ENOMEM);
 	}
 
+	/* Save the compatible histogram information */
 	var_hist->hist_data = hist_data;
 
+	/* Create the new histogram with our variable */
 	ret = event_hist_trigger_func(&trigger_hist_cmd, file,
 				      "", "hist", cmd);
 	if (ret) {
@@ -2798,20 +3002,21 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
 		kfree(var_hist->cmd);
 		kfree(var_hist);
 		hist_err_event("onmatch: Couldn't create histogram for field: ",
-			       system, event_name, field_name);
+			       subsys_name, event_name, field_name);
 		return ERR_PTR(ret);
 	}
 
-	strcpy(cmd, "synthetic_");
-	strcat(cmd, field_name);
+	kfree(cmd);
 
-	event_var = find_event_var(tr, system, event_name, cmd);
-	if (!event_var) {
+	/* If we can't find the variable, something went wrong */
+	event_var = find_synthetic_field_var(target_hist_data, subsys_name,
+					     event_name, field_name);
+	if (!event_var || IS_ERR(event_var)) {
 		kfree(cmd);
 		kfree(var_hist->cmd);
 		kfree(var_hist);
 		hist_err_event("onmatch: Couldn't find synthetic variable: ",
-			       system, event_name, field_name);
+			       subsys_name, event_name, field_name);
 		return ERR_PTR(-EINVAL);
 	}
 
@@ -2824,12 +3029,12 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
 
 static struct hist_field *
 find_target_event_var(struct hist_trigger_data *hist_data,
-		      char *system, char *event_name, char *var_name)
+		      char *subsys_name, char *event_name, char *var_name)
 {
 	struct trace_event_file *file = hist_data->event_file;
 	struct hist_field *hist_field = NULL;
 
-	if (system) {
+	if (subsys_name) {
 		struct trace_event_call *call;
 
 		if (!event_name)
@@ -2837,7 +3042,7 @@ find_target_event_var(struct hist_trigger_data *hist_data,
 
 		call = file->event_call;
 
-		if (strcmp(system, call->class->system) != 0)
+		if (strcmp(subsys_name, call->class->system) != 0)
 			return NULL;
 
 		if (strcmp(event_name, trace_event_name(call)) != 0)
@@ -2904,7 +3109,7 @@ static struct hist_field *create_var(struct hist_trigger_data *hist_data,
 	struct hist_field *var;
 	int idx;
 
-	if (find_var(file, name) && !hist_data->remove) {
+	if (find_var(hist_data, file, name) && !hist_data->remove) {
 		var = ERR_PTR(-EINVAL);
 		goto out;
 	}
@@ -2985,13 +3190,33 @@ static struct field_var *create_field_var(struct hist_trigger_data *hist_data,
 	goto out;
 }
 
-static struct field_var *
-create_target_field_var(struct hist_trigger_data *hist_data,
-			char *system, char *event_name, char *var_name)
-{
-	struct trace_event_file *file = hist_data->event_file;
+/**
+ * create_target_field_var - Automatically create a variable for a field
+ * @target_hist_data: The target hist trigger
+ * @subsys_name: Optional subsystem name
+ * @event_name: Optional event name
+ * @var_name: The name of the field (and the resulting variable)
+ *
+ * Hist trigger actions fetch data from variables, not directly from
+ * events.  However, for convenience, users are allowed to directly
+ * specify an event field in an action, which will be automatically
+ * converted into a variable on their behalf.
 
-	if (system) {
+ * This function creates a field variable with the name var_name on
+ * the hist trigger currently being defined on the target event.  If
+ * subsys_name and event_name are specified, this function simply
+ * verifies that they do in fact match the target event subsystem and
+ * event name.
+ *
+ * Return: The variable created for the field.
+ */
+static struct field_var *
+create_target_field_var(struct hist_trigger_data *target_hist_data,
+			char *subsys_name, char *event_name, char *var_name)
+{
+	struct trace_event_file *file = target_hist_data->event_file;
+
+	if (subsys_name) {
 		struct trace_event_call *call;
 
 		if (!event_name)
@@ -2999,14 +3224,14 @@ create_target_field_var(struct hist_trigger_data *hist_data,
 
 		call = file->event_call;
 
-		if (strcmp(system, call->class->system) != 0)
+		if (strcmp(subsys_name, call->class->system) != 0)
 			return NULL;
 
 		if (strcmp(event_name, trace_event_name(call)) != 0)
 			return NULL;
 	}
 
-	return create_field_var(hist_data, file, var_name);
+	return create_field_var(target_hist_data, file, var_name);
 }
 
 static void onmax_print(struct seq_file *m,
@@ -3105,7 +3330,7 @@ static int onmax_create(struct hist_trigger_data *hist_data,
 	if (!ref_field)
 		return -ENOMEM;
 
-	if (init_var_ref(ref_field, var_field)) {
+	if (init_var_ref(ref_field, var_field, NULL, NULL)) {
 		destroy_hist_field(ref_field, 0);
 		ret = -ENOMEM;
 		goto out;
@@ -3145,8 +3370,6 @@ static int onmax_create(struct hist_trigger_data *hist_data,
 
 		kfree(param);
 	}
-
-	hist_data->actions[hist_data->n_actions++] = data;
  out:
 	return ret;
 }
@@ -3327,7 +3550,6 @@ static struct hist_field *
 onmatch_find_var(struct hist_trigger_data *hist_data, struct action_data *data,
 		 char *system, char *event, char *var)
 {
-	struct trace_array *tr = hist_data->event_file->tr;
 	struct hist_field *hist_field;
 
 	var++; /* skip '$' */
@@ -3339,7 +3561,7 @@ onmatch_find_var(struct hist_trigger_data *hist_data, struct action_data *data,
 			event = data->onmatch.match_event;
 		}
 
-		hist_field = find_event_var(tr, system, event, var);
+		hist_field = find_event_var(hist_data, system, event, var);
 	}
 
 	if (!hist_field)
@@ -3356,19 +3578,36 @@ onmatch_create_field_var(struct hist_trigger_data *hist_data,
 	struct hist_field *hist_field = NULL;
 	struct field_var *field_var;
 
+	/*
+	 * First try to create a field var on the target event (the
+	 * currently being defined).  This will create a variable for
+	 * unqualified fields on the target event, or if qualified,
+	 * target fields that have qualified names matching the target.
+	 */
 	field_var = create_target_field_var(hist_data, system, event, var);
-	if (IS_ERR(field_var))
-		goto out;
 
-	if (field_var) {
+	if (field_var && !IS_ERR(field_var)) {
 		save_field_var(hist_data, field_var);
 		hist_field = field_var->var;
 	} else {
+		field_var = NULL;
+		/*
+		 * If no explicit system.event is specfied, default to
+		 * looking for fields on the onmatch(system.event.xxx)
+		 * event.
+		 */
 		if (!system) {
 			system = data->onmatch.match_event_system;
 			event = data->onmatch.match_event;
 		}
 
+		/*
+		 * At this point, we're looking at a field on another
+		 * event.  Because we can't modify a hist trigger on
+		 * another event to add a variable for a field, we need
+		 * to create a new trigger on that event and create the
+		 * variable at the same time.
+		 */
 		hist_field = create_field_var_hist(hist_data, system, event, var);
 		if (IS_ERR(hist_field))
 			goto free;
@@ -3441,7 +3680,7 @@ static int onmatch_create(struct hist_trigger_data *hist_data,
 		}
 
 		if (check_synth_field(event, hist_field, field_pos) == 0) {
-			var_ref = create_var_ref(hist_field);
+			var_ref = create_var_ref(hist_field, system, event_name);
 			if (!var_ref) {
 				kfree(p);
 				ret = -ENOMEM;
@@ -3470,7 +3709,6 @@ static int onmatch_create(struct hist_trigger_data *hist_data,
 	data->fn = action_trace;
 	data->onmatch.synth_event = event;
 	data->onmatch.var_ref_idx = var_ref_idx;
-	hist_data->actions[hist_data->n_actions++] = data;
 	event->ref++;
  out:
 	return ret;
@@ -3588,9 +3826,6 @@ static int __create_val_field(struct hist_trigger_data *hist_data,
 	++hist_data->n_vals;
 	++hist_data->n_fields;
 
-	if (hist_field->flags & HIST_FIELD_FL_VAR_ONLY)
-		hist_data->n_var_only++;
-
 	if (WARN_ON(hist_data->n_vals > TRACING_MAP_VALS_MAX + TRACING_MAP_VARS_MAX))
 		ret = -EINVAL;
  out:
@@ -3618,19 +3853,15 @@ static int create_var_field(struct hist_trigger_data *hist_data,
 	if (WARN_ON(val_idx >= TRACING_MAP_VALS_MAX + TRACING_MAP_VARS_MAX))
 		return -EINVAL;
 
-	if (find_var(file, var_name) && !hist_data->remove) {
+	if (find_var(hist_data, file, var_name) && !hist_data->remove) {
 		hist_err("Variable already defined: ", var_name);
 		return -EINVAL;
 	}
 
 	flags |= HIST_FIELD_FL_VAR;
 	hist_data->n_vars++;
-	if (hist_data->n_vars > TRACING_MAP_VARS_MAX) {
-		hist_err("Too many variables defined: ", var_name);
+	if (WARN_ON(hist_data->n_vars > TRACING_MAP_VARS_MAX))
 		return -EINVAL;
-	}
-
-	flags |= HIST_FIELD_FL_VAR_ONLY;
 
 	return __create_val_field(hist_data, val_idx, file, var_name, expr_str, flags);
 }
@@ -3704,6 +3935,7 @@ static int create_key_field(struct hist_trigger_data *hist_data,
 		}
 
 		if (hist_field->flags & HIST_FIELD_FL_VAR_REF) {
+			hist_err("Using variable references as keys not supported: ", field_str);
 			destroy_hist_field(hist_field, 0);
 			ret = -EINVAL;
 			goto out;
@@ -3822,6 +4054,12 @@ static int parse_var_defs(struct hist_trigger_data *hist_data)
 				goto free;
 			}
 
+			if (n_vars == TRACING_MAP_VARS_MAX) {
+				hist_err("Too many variables defined: ", var_name);
+				ret = -EINVAL;
+				goto free;
+			}
+
 			s = kstrdup(var_name, GFP_KERNEL);
 			if (!s) {
 				ret = -ENOMEM;
@@ -3831,15 +4069,13 @@ static int parse_var_defs(struct hist_trigger_data *hist_data)
 
 			s = kstrdup(field_str, GFP_KERNEL);
 			if (!s) {
+				kfree(hist_data->attrs->var_defs.name[n_vars]);
 				ret = -ENOMEM;
 				goto free;
 			}
 			hist_data->attrs->var_defs.expr[n_vars++] = s;
 
 			hist_data->attrs->var_defs.n_vars = n_vars;
-
-			if (n_vars == TRACING_MAP_VARS_MAX)
-				goto free;
 		}
 	}
 
@@ -3947,7 +4183,7 @@ static int create_sort_keys(struct hist_trigger_data *hist_data)
 			unsigned int idx;
 
 			hist_field = hist_data->fields[j];
-			if (hist_field->flags & HIST_FIELD_FL_VAR_ONLY)
+			if (hist_field->flags & HIST_FIELD_FL_VAR)
 				continue;
 
 			idx = k++;
@@ -3992,8 +4228,7 @@ static void destroy_actions(struct hist_trigger_data *hist_data)
 	}
 }
 
-static int create_actions(struct hist_trigger_data *hist_data,
-			  struct trace_event_file *file)
+static int parse_actions(struct hist_trigger_data *hist_data)
 {
 	struct trace_array *tr = hist_data->event_file->tr;
 	struct action_data *data;
@@ -4008,26 +4243,49 @@ static int create_actions(struct hist_trigger_data *hist_data,
 			char *action_str = str + strlen("onmatch(");
 
 			data = onmatch_parse(tr, action_str);
-			if (IS_ERR(data))
-				return PTR_ERR(data);
-
-			ret = onmatch_create(hist_data, file, data);
-			if (ret) {
-				onmatch_destroy(data);
-				return ret;
+			if (IS_ERR(data)) {
+				ret = PTR_ERR(data);
+				break;
 			}
+			data->fn = action_trace;
 		} else if (strncmp(str, "onmax(", strlen("onmax(")) == 0) {
 			char *action_str = str + strlen("onmax(");
 
 			data = onmax_parse(action_str);
-			if (IS_ERR(data))
-				return PTR_ERR(data);
-
-			ret = onmax_create(hist_data, data);
-			if (ret) {
-				onmax_destroy(data);
-				return ret;
+			if (IS_ERR(data)) {
+				ret = PTR_ERR(data);
+				break;
 			}
+			data->fn = onmax_save;
+		} else {
+			ret = -EINVAL;
+			break;
+		}
+
+		hist_data->actions[hist_data->n_actions++] = data;
+	}
+
+	return ret;
+}
+
+static int create_actions(struct hist_trigger_data *hist_data,
+			  struct trace_event_file *file)
+{
+	struct action_data *data;
+	unsigned int i;
+	int ret = 0;
+
+	for (i = 0; i < hist_data->attrs->n_actions; i++) {
+		data = hist_data->actions[i];
+
+		if (data->fn == action_trace) {
+			ret = onmatch_create(hist_data, file, data);
+			if (ret)
+				return ret;
+		} else if (data->fn == onmax_save) {
+			ret = onmax_create(hist_data, data);
+			if (ret)
+				return ret;
 		}
 	}
 
@@ -4191,6 +4449,10 @@ create_hist_data(unsigned int map_bits,
 	hist_data->remove = remove;
 	hist_data->event_file = file;
 
+	ret = parse_actions(hist_data);
+	if (ret)
+		goto free;
+
 	ret = create_hist_fields(hist_data, file);
 	if (ret)
 		goto free;
@@ -4243,8 +4505,7 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
 		if (hist_field->flags & HIST_FIELD_FL_VAR) {
 			var_idx = hist_field->var.idx;
 			tracing_map_set_var(elt, var_idx, hist_val);
-			if (hist_field->flags & HIST_FIELD_FL_VAR_ONLY)
-				continue;
+			continue;
 		}
 		tracing_map_update_sum(elt, i, hist_val);
 	}
@@ -4414,7 +4675,12 @@ hist_trigger_entry_print(struct seq_file *m,
 				   uval, str);
 		} else if (key_field->flags & HIST_FIELD_FL_EXECNAME) {
 			struct hist_elt_data *elt_data = elt->private_data;
-			char *comm = elt_data->comm;
+			char *comm;
+
+			if (WARN_ON_ONCE(!elt_data))
+				return;
+
+			comm = elt_data->comm;
 
 			uval = *(u64 *)(key + key_field->offset);
 			seq_printf(m, "%s: %-16s[%10llu]", field_name,
@@ -4459,8 +4725,7 @@ hist_trigger_entry_print(struct seq_file *m,
 		field_name = hist_field_name(hist_data->fields[i], 0);
 
 		if (hist_data->fields[i]->flags & HIST_FIELD_FL_VAR ||
-		    hist_data->fields[i]->flags & HIST_FIELD_FL_EXPR ||
-		    hist_data->fields[i]->flags & HIST_FIELD_FL_VAR_REF)
+		    hist_data->fields[i]->flags & HIST_FIELD_FL_EXPR)
 			continue;
 
 		if (hist_data->fields[i]->flags & HIST_FIELD_FL_HEX) {
@@ -4579,7 +4844,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
 	else if (hist_field->flags & HIST_FIELD_FL_CPU)
 		seq_puts(m, "cpu");
 	else if (field_name) {
-		if (hist_field->flags & HIST_FIELD_FL_ALIAS)
+		if (hist_field->flags & HIST_FIELD_FL_VAR_REF ||
+		    hist_field->flags & HIST_FIELD_FL_ALIAS)
 			seq_putc(m, '$');
 		seq_printf(m, "%s", field_name);
 	}
@@ -4597,8 +4863,8 @@ static int event_hist_trigger_print(struct seq_file *m,
 				    struct event_trigger_data *data)
 {
 	struct hist_trigger_data *hist_data = data->private_data;
-	bool have_var_only = false;
 	struct hist_field *field;
+	bool have_var = false;
 	unsigned int i;
 
 	seq_puts(m, "hist:");
@@ -4624,8 +4890,8 @@ static int event_hist_trigger_print(struct seq_file *m,
 
 	for_each_hist_val_field(i, hist_data) {
 		field = hist_data->fields[i];
-		if (field->flags & HIST_FIELD_FL_VAR_ONLY) {
-			have_var_only = true;
+		if (field->flags & HIST_FIELD_FL_VAR) {
+			have_var = true;
 			continue;
 		}
 
@@ -4637,7 +4903,7 @@ static int event_hist_trigger_print(struct seq_file *m,
 		}
 	}
 
-	if (have_var_only) {
+	if (have_var) {
 		unsigned int n = 0;
 
 		seq_puts(m, ":");
@@ -4645,7 +4911,7 @@ static int event_hist_trigger_print(struct seq_file *m,
 		for_each_hist_val_field(i, hist_data) {
 			field = hist_data->fields[i];
 
-			if (field->flags & HIST_FIELD_FL_VAR_ONLY) {
+			if (field->flags & HIST_FIELD_FL_VAR) {
 				if (n++)
 					seq_puts(m, ",");
 				hist_field_print(m, field);
@@ -4659,8 +4925,8 @@ static int event_hist_trigger_print(struct seq_file *m,
 		struct tracing_map_sort_key *sort_key;
 		unsigned int idx, first_key_idx;
 
-		/* skip VAR_ONLY vals */
-		first_key_idx = hist_data->n_vals - hist_data->n_var_only;
+		/* skip VAR vals */
+		first_key_idx = hist_data->n_vals - hist_data->n_vars;
 
 		sort_key = &hist_data->sort_keys[i];
 		idx = sort_key->field_idx;
@@ -4675,7 +4941,7 @@ static int event_hist_trigger_print(struct seq_file *m,
 			seq_puts(m, "hitcount");
 		else {
 			if (idx >= first_key_idx)
-				idx += hist_data->n_var_only;
+				idx += hist_data->n_vars;
 			hist_field_print(m, hist_data->fields[idx]);
 		}
 
@@ -4969,7 +5235,7 @@ static int hist_trigger_enable(struct event_trigger_data *data,
 {
 	int ret = 0;
 
-	list_add_rcu(&data->list, &file->triggers);
+	list_add_tail_rcu(&data->list, &file->triggers);
 
 	update_cond_flag(file);
 
@@ -4982,6 +5248,28 @@ static int hist_trigger_enable(struct event_trigger_data *data,
 	return ret;
 }
 
+static bool have_hist_trigger_match(struct event_trigger_data *data,
+				    struct trace_event_file *file)
+{
+	struct hist_trigger_data *hist_data = data->private_data;
+	struct event_trigger_data *test, *named_data = NULL;
+	bool match = false;
+
+	if (hist_data->attrs->name)
+		named_data = find_named_trigger(hist_data->attrs->name);
+
+	list_for_each_entry_rcu(test, &file->triggers, list) {
+		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			if (hist_trigger_match(data, test, named_data, false)) {
+				match = true;
+				break;
+			}
+		}
+	}
+
+	return match;
+}
+
 static bool hist_trigger_check_refs(struct event_trigger_data *data,
 				    struct trace_event_file *file)
 {
@@ -5072,18 +5360,32 @@ static bool hist_file_check_refs(struct trace_event_file *file)
 static void hist_unreg_all(struct trace_event_file *file)
 {
 	struct event_trigger_data *test, *n;
+	struct hist_trigger_data *hist_data;
+	struct synth_event *se;
+	const char *se_name;
 
 	if (hist_file_check_refs(file))
 		return;
 
 	list_for_each_entry_safe(test, n, &file->triggers, list) {
 		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
-			unregister_field_var_hists(test->private_data);
+			hist_data = test->private_data;
+			unregister_field_var_hists(hist_data);
 			list_del_rcu(&test->list);
 			trace_event_trigger_enable_disable(file, 0);
+
+			mutex_lock(&synth_event_mutex);
+			se_name = trace_event_name(file->event_call);
+			se = find_synth_event(se_name);
+			if (se)
+				se->ref--;
+			mutex_unlock(&synth_event_mutex);
+
 			update_cond_flag(file);
 			if (test->ops->free)
 				test->ops->free(test->ops, test);
+			if (hist_data->enable_timestamps)
+				tracing_set_time_stamp_abs(file->tr, false);
 		}
 	}
 }
@@ -5118,19 +5420,33 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	 * separate the trigger from the filter (k:v [if filter])
 	 * allowing for whitespace in the trigger
 	 */
-	trigger = param;
-	p = strstr(param, " if");
-	if (!p)
-		p = strstr(param, "\tif");
-	if (p) {
-		if (p == trigger)
+	p = trigger = param;
+	do {
+		p = strstr(p, "if");
+		if (!p)
+			break;
+		if (p == param)
 			return -EINVAL;
-		param = p + 1;
-		param = strstrip(param);
-		*p = '\0';
-		trigger = strstrip(trigger);
-	} else
+		if (*(p - 1) != ' ' && *(p - 1) != '\t') {
+			p++;
+			continue;
+		}
+		if (p >= param + strlen(param) - strlen("if") - 1)
+			return -EINVAL;
+		if (*(p + strlen("if")) != ' ' && *(p + strlen("if")) != '\t') {
+			p++;
+			continue;
+		}
+		break;
+	} while (p);
+
+	if (!p)
 		param = NULL;
+	else {
+		*(p - 1) = '\0';
+		param = strstrip(p);
+		trigger = strstrip(trigger);
+	}
 
 	attrs = parse_hist_trigger_attrs(trigger);
 	if (IS_ERR(attrs))
@@ -5147,10 +5463,11 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 
 	trigger_ops = cmd_ops->get_trigger_ops(cmd, trigger);
 
-	ret = -ENOMEM;
 	trigger_data = kzalloc(sizeof(*trigger_data), GFP_KERNEL);
-	if (!trigger_data)
+	if (!trigger_data) {
+		ret = -ENOMEM;
 		goto out_free;
+	}
 
 	trigger_data->count = -1;
 	trigger_data->ops = trigger_ops;
@@ -5169,6 +5486,9 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	}
 
 	if (remove) {
+		if (!have_hist_trigger_match(trigger_data, file))
+			goto out_free;
+
 		if (hist_trigger_check_refs(trigger_data, file)) {
 			ret = -EBUSY;
 			goto out_free;
@@ -5188,7 +5508,6 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	}
 
 	ret = cmd_ops->reg(glob, trigger_ops, trigger_data, file);
-
 	/*
 	 * The above returns on success the # of triggers registered,
 	 * but if it didn't register any it returns zero.  Consider no
@@ -5201,13 +5520,6 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	} else if (ret < 0)
 		goto out_free;
 
-	mutex_lock(&synth_event_mutex);
-	se_name = trace_event_name(file->event_call);
-	se = find_synth_event(se_name);
-	if (se)
-		se->ref++;
-	mutex_unlock(&synth_event_mutex);
-
 	if (get_named_trigger_data(trigger_data))
 		goto enable;
 
@@ -5226,6 +5538,13 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	if (ret)
 		goto out_unreg;
 
+	mutex_lock(&synth_event_mutex);
+	se_name = trace_event_name(file->event_call);
+	se = find_synth_event(se_name);
+	if (se)
+		se->ref++;
+	mutex_unlock(&synth_event_mutex);
+
 	/* Just return zero, not the number of registered triggers */
 	ret = 0;
  out:
diff --git a/localversion-rt b/localversion-rt
index c3054d08a112..1445cd65885c 100644
--- a/localversion-rt
+++ b/localversion-rt
@@ -1 +1 @@
--rt2
+-rt3
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 25e0fd082f13..27549bf47139 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1723,7 +1723,6 @@ struct memcg_stock_pcp {
 #define FLUSHING_CACHED_CHARGE	0
 };
 static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
-static DEFINE_LOCAL_IRQ_LOCK(memcg_stock_ll);
 static DEFINE_MUTEX(percpu_charge_mutex);
 
 /**
@@ -1746,7 +1745,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 	if (nr_pages > CHARGE_BATCH)
 		return ret;
 
-	local_lock_irqsave(memcg_stock_ll, flags);
+	local_irq_save(flags);
 
 	stock = this_cpu_ptr(&memcg_stock);
 	if (memcg == stock->cached && stock->nr_pages >= nr_pages) {
@@ -1754,7 +1753,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 		ret = true;
 	}
 
-	local_unlock_irqrestore(memcg_stock_ll, flags);
+	local_irq_restore(flags);
 
 	return ret;
 }
@@ -1785,13 +1784,13 @@ static void drain_local_stock(struct work_struct *dummy)
 	 * The only protection from memory hotplug vs. drain_stock races is
 	 * that we always operate on local CPU stock here with IRQ disabled
 	 */
-	local_lock_irqsave(memcg_stock_ll, flags);
+	local_irq_save(flags);
 
 	stock = this_cpu_ptr(&memcg_stock);
 	drain_stock(stock);
 	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
 
-	local_unlock_irqrestore(memcg_stock_ll, flags);
+	local_irq_restore(flags);
 }
 
 /*
@@ -1803,7 +1802,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 	struct memcg_stock_pcp *stock;
 	unsigned long flags;
 
-	local_lock_irqsave(memcg_stock_ll, flags);
+	local_irq_save(flags);
 
 	stock = this_cpu_ptr(&memcg_stock);
 	if (stock->cached != memcg) { /* reset if necessary */
@@ -1815,7 +1814,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 	if (stock->nr_pages > CHARGE_BATCH)
 		drain_stock(stock);
 
-	local_unlock_irqrestore(memcg_stock_ll, flags);
+	local_irq_restore(flags);
 }
 
 /*
diff --git a/tools/testing/selftests/ftrace/test.d/functions b/tools/testing/selftests/ftrace/test.d/functions
index f2019b37370d..17afa65c0b41 100644
--- a/tools/testing/selftests/ftrace/test.d/functions
+++ b/tools/testing/selftests/ftrace/test.d/functions
@@ -55,6 +55,13 @@ disable_events() {
     echo 0 > events/enable
 }
 
+clear_synthetic_events() { # reset all current synthetic events
+    grep -v ^# synthetic_events |
+    while read line; do
+        echo "!$line" >> synthetic_events
+    done
+}
+
 initialize_ftrace() { # Reset ftrace to initial-state
 # As the initial state, ftrace will be set to nop tracer,
 # no events, no triggers, no filters, no function filters,
diff --git a/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-extended-error-support.tc b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-extended-error-support.tc
new file mode 100644
index 000000000000..f7691ffcef9c
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-extended-error-support.tc
@@ -0,0 +1,39 @@
+#!/bin/sh
+# description: event trigger - test extended error support
+
+
+do_reset() {
+    reset_trigger
+    echo > set_event
+    clear_trace
+}
+
+fail() { #msg
+    do_reset
+    echo $1
+    exit_fail
+}
+
+if [ ! -f set_event ]; then
+    echo "event tracing is not supported"
+    exit_unsupported
+fi
+
+if [ ! -f synthetic_events ]; then
+    echo "synthetic event is not supported"
+    exit_unsupported
+fi
+
+reset_tracer
+do_reset
+
+echo "Test extended error support"
+echo 'hist:keys=pid:ts0=$common_timestamp.usecs if comm=="ping"' > events/sched/sched_wakeup/trigger
+echo 'hist:keys=pid:ts0=$common_timestamp.usecs if comm=="ping"' >> events/sched/sched_wakeup/trigger &>/dev/null
+if ! grep -q "ERROR:" events/sched/sched_wakeup/hist; then
+    fail "Failed to generate extended error in histogram"
+fi
+
+do_reset
+
+exit 0
diff --git a/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-field-variable-support.tc b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-field-variable-support.tc
new file mode 100644
index 000000000000..46657334ba9a
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-field-variable-support.tc
@@ -0,0 +1,54 @@
+#!/bin/sh
+# description: event trigger - test field variable support
+
+do_reset() {
+    reset_trigger
+    echo > set_event
+    clear_trace
+}
+
+fail() { #msg
+    do_reset
+    echo $1
+    exit_fail
+}
+
+if [ ! -f set_event ]; then
+    echo "event tracing is not supported"
+    exit_unsupported
+fi
+
+if [ ! -f synthetic_events ]; then
+    echo "synthetic event is not supported"
+    exit_unsupported
+fi
+
+clear_synthetic_events
+reset_tracer
+do_reset
+
+echo "Test field variable support"
+
+echo 'wakeup_latency u64 lat; pid_t pid; int prio; char comm[16]' > synthetic_events
+echo 'hist:keys=comm:ts0=$common_timestamp.usecs if comm=="ping"' > events/sched/sched_waking/trigger
+echo 'hist:keys=next_comm:wakeup_lat=$common_timestamp.usecs-$ts0:onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,next_pid,sched.sched_waking.prio,next_comm) if next_comm=="ping"' > events/sched/sched_switch/trigger
+echo 'hist:keys=pid,prio,comm:vals=lat:sort=pid,prio' > events/synthetic/wakeup_latency/trigger
+
+ping localhost -c 3
+if ! grep -q "ping" events/synthetic/wakeup_latency/hist; then
+    fail "Failed to create inter-event histogram"
+fi
+
+if ! grep -q "synthetic_prio=prio" events/sched/sched_waking/hist; then
+    fail "Failed to create histogram with field variable"
+fi
+
+echo '!hist:keys=next_comm:wakeup_lat=$common_timestamp.usecs-$ts0:onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,next_pid,sched.sched_waking.prio,next_comm) if next_comm=="ping"' >> events/sched/sched_switch/trigger
+
+if grep -q "synthetic_prio=prio" events/sched/sched_waking/hist; then
+    fail "Failed to remove histogram with field variable"
+fi
+
+do_reset
+
+exit 0
diff --git a/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-inter-event-combined-hist.tc b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-inter-event-combined-hist.tc
new file mode 100644
index 000000000000..8d00064aa0b6
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-inter-event-combined-hist.tc
@@ -0,0 +1,58 @@
+#!/bin/sh
+# description: event trigger - test inter-event combined histogram trigger
+
+do_reset() {
+    reset_trigger
+    echo > set_event
+    clear_trace
+}
+
+fail() { #msg
+    do_reset
+    echo $1
+    exit_fail
+}
+
+if [ ! -f set_event ]; then
+    echo "event tracing is not supported"
+    exit_unsupported
+fi
+
+if [ ! -f synthetic_events ]; then
+    echo "synthetic event is not supported"
+    exit_unsupported
+fi
+
+reset_tracer
+do_reset
+clear_synthetic_events
+
+echo "Test create synthetic event"
+
+echo 'waking_latency  u64 lat pid_t pid' > synthetic_events
+if [ ! -d events/synthetic/waking_latency ]; then
+    fail "Failed to create waking_latency synthetic event"
+fi
+
+echo "Test combined histogram"
+
+echo 'hist:keys=pid:ts0=$common_timestamp.usecs if comm=="ping"' > events/sched/sched_waking/trigger
+echo 'hist:keys=pid:waking_lat=$common_timestamp.usecs-$ts0:onmatch(sched.sched_waking).waking_latency($waking_lat,pid) if comm=="ping"' > events/sched/sched_wakeup/trigger
+echo 'hist:keys=pid,lat:sort=pid,lat' > events/synthetic/waking_latency/trigger
+
+echo 'wakeup_latency u64 lat pid_t pid' >> synthetic_events
+echo 'hist:keys=pid:ts1=$common_timestamp.usecs if comm=="ping"' >> events/sched/sched_wakeup/trigger
+echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp.usecs-$ts1:onmatch(sched.sched_wakeup).wakeup_latency($wakeup_lat,next_pid) if next_comm=="ping"' > events/sched/sched_switch/trigger
+
+echo 'waking+wakeup_latency u64 lat; pid_t pid' >> synthetic_events
+echo 'hist:keys=pid,lat:sort=pid,lat:ww_lat=$waking_lat+$wakeup_lat:onmatch(synthetic.wakeup_latency).waking+wakeup_latency($ww_lat,pid)' >> events/synthetic/wakeup_latency/trigger
+echo 'hist:keys=pid,lat:sort=pid,lat' >> events/synthetic/waking+wakeup_latency/trigger
+
+ping localhost -c 3
+if ! grep -q "pid:" events/synthetic/waking+wakeup_latency/hist; then
+    fail "Failed to create combined histogram"
+fi
+
+do_reset
+
+exit 0
diff --git a/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmatch-action-hist.tc b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmatch-action-hist.tc
new file mode 100644
index 000000000000..ac13051d9cf8
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmatch-action-hist.tc
@@ -0,0 +1,50 @@
+#!/bin/sh
+# description: event trigger - test inter-event histogram trigger onmatch action
+
+do_reset() {
+    reset_trigger
+    echo > set_event
+    clear_trace
+}
+
+fail() { #msg
+    do_reset
+    echo $1
+    exit_fail
+}
+
+if [ ! -f set_event ]; then
+    echo "event tracing is not supported"
+    exit_unsupported
+fi
+
+if [ ! -f synthetic_events ]; then
+    echo "synthetic event is not supported"
+    exit_unsupported
+fi
+
+clear_synthetic_events
+reset_tracer
+do_reset
+
+echo "Test create synthetic event"
+
+echo 'wakeup_latency  u64 lat pid_t pid char comm[16]' > synthetic_events
+if [ ! -d events/synthetic/wakeup_latency ]; then
+    fail "Failed to create wakeup_latency synthetic event"
+fi
+
+echo "Test create histogram for synthetic event"
+echo "Test histogram variables,simple expression support and onmatch action"
+
+echo 'hist:keys=pid:ts0=$common_timestamp.usecs if comm=="ping"' > events/sched/sched_wakeup/trigger
+echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp.usecs-$ts0:onmatch(sched.sched_wakeup).wakeup_latency($wakeup_lat,next_pid,next_comm) if next_comm=="ping"' > events/sched/sched_switch/trigger
+echo 'hist:keys=comm,pid,lat:wakeup_lat=lat:sort=lat' > events/synthetic/wakeup_latency/trigger
+ping localhost -c 5
+if ! grep -q "ping" events/synthetic/wakeup_latency/hist; then
+    fail "Failed to create onmatch action inter-event histogram"
+fi
+
+do_reset
+
+exit 0
diff --git a/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmatch-onmax-action-hist.tc b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmatch-onmax-action-hist.tc
new file mode 100644
index 000000000000..39bf19d5cc2c
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmatch-onmax-action-hist.tc
@@ -0,0 +1,50 @@
+#!/bin/sh
+# description: event trigger - test inter-event histogram trigger onmatch-onmax action
+
+do_reset() {
+    reset_trigger
+    echo > set_event
+    clear_trace
+}
+
+fail() { #msg
+    do_reset
+    echo $1
+    exit_fail
+}
+
+if [ ! -f set_event ]; then
+    echo "event tracing is not supported"
+    exit_unsupported
+fi
+
+if [ ! -f synthetic_events ]; then
+    echo "synthetic event is not supported"
+    exit_unsupported
+fi
+
+clear_synthetic_events
+reset_tracer
+do_reset
+
+echo "Test create synthetic event"
+
+echo 'wakeup_latency  u64 lat pid_t pid char comm[16]' > synthetic_events
+if [ ! -d events/synthetic/wakeup_latency ]; then
+    fail "Failed to create wakeup_latency synthetic event"
+fi
+
+echo "Test create histogram for synthetic event"
+echo "Test histogram variables,simple expression support and onmatch-onmax action"
+
+echo 'hist:keys=pid:ts0=$common_timestamp.usecs if comm=="ping"' > events/sched/sched_wakeup/trigger
+echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp.usecs-$ts0:onmatch(sched.sched_wakeup).wakeup_latency($wakeup_lat,next_pid,next_comm):onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) if next_comm=="ping"' >> events/sched/sched_switch/trigger
+echo 'hist:keys=comm,pid,lat:wakeup_lat=lat:sort=lat' > events/synthetic/wakeup_latency/trigger
+ping localhost -c 5
+if [ ! grep -q "ping" events/synthetic/wakeup_latency/hist -o ! grep -q "max:" events/sched/sched_switch/hist]; then
+    fail "Failed to create onmatch-onmax action inter-event histogram"
+fi
+
+do_reset
+
+exit 0
diff --git a/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmax-action-hist.tc b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmax-action-hist.tc
new file mode 100644
index 000000000000..65f55a53126e
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-onmax-action-hist.tc
@@ -0,0 +1,48 @@
+#!/bin/sh
+# description: event trigger - test inter-event histogram trigger onmax action
+
+do_reset() {
+    reset_trigger
+    echo > set_event
+    clear_trace
+}
+
+fail() { #msg
+    do_reset
+    echo $1
+    exit_fail
+}
+
+if [ ! -f set_event ]; then
+    echo "event tracing is not supported"
+    exit_unsupported
+fi
+
+if [ ! -f synthetic_events ]; then
+    echo "synthetic event is not supported"
+    exit_unsupported
+fi
+
+clear_synthetic_events
+reset_tracer
+do_reset
+
+echo "Test create synthetic event"
+
+echo 'wakeup_latency  u64 lat pid_t pid char comm[16]' > synthetic_events
+if [ ! -d events/synthetic/wakeup_latency ]; then
+    fail "Failed to create wakeup_latency synthetic event"
+fi
+
+echo "Test onmax action"
+
+echo 'hist:keys=pid:ts0=$common_timestamp.usecs if comm=="ping"' >> events/sched/sched_waking/trigger
+echo 'hist:keys=next_pid:wakeup_lat=$common_timestamp.usecs-$ts0:onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) if next_comm=="ping"' >> events/sched/sched_switch/trigger
+ping localhost -c 3
+if ! grep -q "max:" events/sched/sched_switch/hist; then
+    fail "Failed to create onmax action inter-event histogram"
+fi
+
+do_reset
+
+exit 0
diff --git a/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-synthetic-event-createremove.tc b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-synthetic-event-createremove.tc
new file mode 100644
index 000000000000..cef11377dcbd
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-synthetic-event-createremove.tc
@@ -0,0 +1,54 @@
+#!/bin/sh
+# description: event trigger - test synthetic event create remove
+do_reset() {
+    reset_trigger
+    echo > set_event
+    clear_trace
+}
+
+fail() { #msg
+    do_reset
+    echo $1
+    exit_fail
+}
+
+if [ ! -f set_event ]; then
+    echo "event tracing is not supported"
+    exit_unsupported
+fi
+
+if [ ! -f synthetic_events ]; then
+    echo "synthetic event is not supported"
+    exit_unsupported
+fi
+
+clear_synthetic_events
+reset_tracer
+do_reset
+
+echo "Test create synthetic event"
+
+echo 'wakeup_latency  u64 lat pid_t pid char comm[16]' > synthetic_events
+if [ ! -d events/synthetic/wakeup_latency ]; then
+    fail "Failed to create wakeup_latency synthetic event"
+fi
+
+reset_trigger
+
+echo "Test create synthetic event with an error"
+echo 'wakeup_latency  u64 lat pid_t pid char' > synthetic_events > /dev/null
+if [ -d events/synthetic/wakeup_latency ]; then
+    fail "Created wakeup_latency synthetic event with an invalid format"
+fi
+
+reset_trigger
+
+echo "Test remove synthetic event"
+echo '!wakeup_latency  u64 lat pid_t pid char comm[16]' > synthetic_events
+if [ -d events/synthetic/wakeup_latency ]; then
+    fail "Failed to delete wakeup_latency synthetic event"
+fi
+
+do_reset
+
+exit 0
