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Event Histograms
Documentation written by Tom Zanussi
1. Introduction
===============
Histogram triggers are special event triggers that can be used to
aggregate trace event data into histograms. For information on
trace events and event triggers, see Documentation/trace/events.txt.
2. Histogram Trigger Command
============================
A histogram trigger command is an event trigger command that
aggregates event hits into a hash table keyed on one or more trace
event format fields (or stacktrace) and a set of running totals
derived from one or more trace event format fields and/or event
counts (hitcount).
The format of a hist trigger is as follows:
hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>]
[:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue]
[:clear][:name=histname1] [if <filter>]
When a matching event is hit, an entry is added to a hash table
using the key(s) and value(s) named. Keys and values correspond to
fields in the event's format description. Values must correspond to
numeric fields - on an event hit, the value(s) will be added to a
sum kept for that field. The special string 'hitcount' can be used
in place of an explicit value field - this is simply a count of
event hits. If 'values' isn't specified, an implicit 'hitcount'
value will be automatically created and used as the only value.
Keys can be any field, or the special string 'stacktrace', which
will use the event's kernel stacktrace as the key. The keywords
'keys' or 'key' can be used to specify keys, and the keywords
'values', 'vals', or 'val' can be used to specify values. Compound
keys consisting of up to two fields can be specified by the 'keys'
keyword. Hashing a compound key produces a unique entry in the
table for each unique combination of component keys, and can be
useful for providing more fine-grained summaries of event data.
Additionally, sort keys consisting of up to two fields can be
specified by the 'sort' keyword. If more than one field is
specified, the result will be a 'sort within a sort': the first key
is taken to be the primary sort key and the second the secondary
key. If a hist trigger is given a name using the 'name' parameter,
its histogram data will be shared with other triggers of the same
name, and trigger hits will update this common data. Only triggers
with 'compatible' fields can be combined in this way; triggers are
'compatible' if the fields named in the trigger share the same
number and type of fields and those fields also have the same names.
Note that any two events always share the compatible 'hitcount' and
'stacktrace' fields and can therefore be combined using those
fields, however pointless that may be.
'hist' triggers add a 'hist' file to each event's subdirectory.
Reading the 'hist' file for the event will dump the hash table in
its entirety to stdout. If there are multiple hist triggers
attached to an event, there will be a table for each trigger in the
output. The table displayed for a named trigger will be the same as
any other instance having the same name. Each printed hash table
entry is a simple list of the keys and values comprising the entry;
keys are printed first and are delineated by curly braces, and are
followed by the set of value fields for the entry. By default,
numeric fields are displayed as base-10 integers. This can be
modified by appending any of the following modifiers to the field
name:
.hex display a number as a hex value
.sym display an address as a symbol
.sym-offset display an address as a symbol and offset
.syscall display a syscall id as a system call name
.execname display a common_pid as a program name
.log2 display log2 value rather than raw number
.usecs display a common_timestamp in microseconds
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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: