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    Subject[PATCH v7 01/37] tracing: Move hist trigger Documentation to histogram.txt
    Date
    The hist trigger Documentation takes up a large part of events.txt -
    since it will be getting even larger, move it to a separate file.

    Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
    ---
    Documentation/trace/events.txt | 1548 +-----------------------------------
    Documentation/trace/histogram.txt | 1568 +++++++++++++++++++++++++++++++++++++
    2 files changed, 1569 insertions(+), 1547 deletions(-)
    create mode 100644 Documentation/trace/histogram.txt

    diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt
    index 2cc08d4..e28f7f2 100644
    --- a/Documentation/trace/events.txt
    +++ b/Documentation/trace/events.txt
    @@ -517,1550 +517,4 @@ The following commands are supported:
    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
    -
    - 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.
    -
    -
    -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
    + See Documentation/trace/histogram.txt for details and examples.
    diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt
    new file mode 100644
    index 0000000..b2145f4
    --- /dev/null
    +++ b/Documentation/trace/histogram.txt
    @@ -0,0 +1,1568 @@
    + 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
    +
    + 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.
    +
    +
    +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
    --
    1.9.3
    \
     
     \ /
      Last update: 2017-12-06 23:38    [W:5.431 / U:0.124 seconds]
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