0001 ================
0002 Event Histograms
0003 ================
0004
0005 Documentation written by Tom Zanussi
0006
0007 1. Introduction
0008 ===============
0009
0010 Histogram triggers are special event triggers that can be used to
0011 aggregate trace event data into histograms. For information on
0012 trace events and event triggers, see Documentation/trace/events.rst.
0013
0014
0015 2. Histogram Trigger Command
0016 ============================
0017
0018 A histogram trigger command is an event trigger command that
0019 aggregates event hits into a hash table keyed on one or more trace
0020 event format fields (or stacktrace) and a set of running totals
0021 derived from one or more trace event format fields and/or event
0022 counts (hitcount).
0023
0024 The format of a hist trigger is as follows::
0025
0026 hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>]
0027 [:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue]
0028 [:clear][:name=histname1][:<handler>.<action>] [if <filter>]
0029
0030 When a matching event is hit, an entry is added to a hash table
0031 using the key(s) and value(s) named. Keys and values correspond to
0032 fields in the event's format description. Values must correspond to
0033 numeric fields - on an event hit, the value(s) will be added to a
0034 sum kept for that field. The special string 'hitcount' can be used
0035 in place of an explicit value field - this is simply a count of
0036 event hits. If 'values' isn't specified, an implicit 'hitcount'
0037 value will be automatically created and used as the only value.
0038 Keys can be any field, or the special string 'stacktrace', which
0039 will use the event's kernel stacktrace as the key. The keywords
0040 'keys' or 'key' can be used to specify keys, and the keywords
0041 'values', 'vals', or 'val' can be used to specify values. Compound
0042 keys consisting of up to two fields can be specified by the 'keys'
0043 keyword. Hashing a compound key produces a unique entry in the
0044 table for each unique combination of component keys, and can be
0045 useful for providing more fine-grained summaries of event data.
0046 Additionally, sort keys consisting of up to two fields can be
0047 specified by the 'sort' keyword. If more than one field is
0048 specified, the result will be a 'sort within a sort': the first key
0049 is taken to be the primary sort key and the second the secondary
0050 key. If a hist trigger is given a name using the 'name' parameter,
0051 its histogram data will be shared with other triggers of the same
0052 name, and trigger hits will update this common data. Only triggers
0053 with 'compatible' fields can be combined in this way; triggers are
0054 'compatible' if the fields named in the trigger share the same
0055 number and type of fields and those fields also have the same names.
0056 Note that any two events always share the compatible 'hitcount' and
0057 'stacktrace' fields and can therefore be combined using those
0058 fields, however pointless that may be.
0059
0060 'hist' triggers add a 'hist' file to each event's subdirectory.
0061 Reading the 'hist' file for the event will dump the hash table in
0062 its entirety to stdout. If there are multiple hist triggers
0063 attached to an event, there will be a table for each trigger in the
0064 output. The table displayed for a named trigger will be the same as
0065 any other instance having the same name. Each printed hash table
0066 entry is a simple list of the keys and values comprising the entry;
0067 keys are printed first and are delineated by curly braces, and are
0068 followed by the set of value fields for the entry. By default,
0069 numeric fields are displayed as base-10 integers. This can be
0070 modified by appending any of the following modifiers to the field
0071 name:
0072
0073 ============= =================================================
0074 .hex display a number as a hex value
0075 .sym display an address as a symbol
0076 .sym-offset display an address as a symbol and offset
0077 .syscall display a syscall id as a system call name
0078 .execname display a common_pid as a program name
0079 .log2 display log2 value rather than raw number
0080 .buckets=size display grouping of values rather than raw number
0081 .usecs display a common_timestamp in microseconds
0082 ============= =================================================
0083
0084 Note that in general the semantics of a given field aren't
0085 interpreted when applying a modifier to it, but there are some
0086 restrictions to be aware of in this regard:
0087
0088 - only the 'hex' modifier can be used for values (because values
0089 are essentially sums, and the other modifiers don't make sense
0090 in that context).
0091 - the 'execname' modifier can only be used on a 'common_pid'. The
0092 reason for this is that the execname is simply the 'comm' value
0093 saved for the 'current' process when an event was triggered,
0094 which is the same as the common_pid value saved by the event
0095 tracing code. Trying to apply that comm value to other pid
0096 values wouldn't be correct, and typically events that care save
0097 pid-specific comm fields in the event itself.
0098
0099 A typical usage scenario would be the following to enable a hist
0100 trigger, read its current contents, and then turn it off::
0101
0102 # echo 'hist:keys=skbaddr.hex:vals=len' > \
0103 /sys/kernel/debug/tracing/events/net/netif_rx/trigger
0104
0105 # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
0106
0107 # echo '!hist:keys=skbaddr.hex:vals=len' > \
0108 /sys/kernel/debug/tracing/events/net/netif_rx/trigger
0109
0110 The trigger file itself can be read to show the details of the
0111 currently attached hist trigger. This information is also displayed
0112 at the top of the 'hist' file when read.
0113
0114 By default, the size of the hash table is 2048 entries. The 'size'
0115 parameter can be used to specify more or fewer than that. The units
0116 are in terms of hashtable entries - if a run uses more entries than
0117 specified, the results will show the number of 'drops', the number
0118 of hits that were ignored. The size should be a power of 2 between
0119 128 and 131072 (any non- power-of-2 number specified will be rounded
0120 up).
0121
0122 The 'sort' parameter can be used to specify a value field to sort
0123 on. The default if unspecified is 'hitcount' and the default sort
0124 order is 'ascending'. To sort in the opposite direction, append
0125 .descending' to the sort key.
0126
0127 The 'pause' parameter can be used to pause an existing hist trigger
0128 or to start a hist trigger but not log any events until told to do
0129 so. 'continue' or 'cont' can be used to start or restart a paused
0130 hist trigger.
0131
0132 The 'clear' parameter will clear the contents of a running hist
0133 trigger and leave its current paused/active state.
0134
0135 Note that the 'pause', 'cont', and 'clear' parameters should be
0136 applied using 'append' shell operator ('>>') if applied to an
0137 existing trigger, rather than via the '>' operator, which will cause
0138 the trigger to be removed through truncation.
0139
0140 - enable_hist/disable_hist
0141
0142 The enable_hist and disable_hist triggers can be used to have one
0143 event conditionally start and stop another event's already-attached
0144 hist trigger. Any number of enable_hist and disable_hist triggers
0145 can be attached to a given event, allowing that event to kick off
0146 and stop aggregations on a host of other events.
0147
0148 The format is very similar to the enable/disable_event triggers::
0149
0150 enable_hist:<system>:<event>[:count]
0151 disable_hist:<system>:<event>[:count]
0152
0153 Instead of enabling or disabling the tracing of the target event
0154 into the trace buffer as the enable/disable_event triggers do, the
0155 enable/disable_hist triggers enable or disable the aggregation of
0156 the target event into a hash table.
0157
0158 A typical usage scenario for the enable_hist/disable_hist triggers
0159 would be to first set up a paused hist trigger on some event,
0160 followed by an enable_hist/disable_hist pair that turns the hist
0161 aggregation on and off when conditions of interest are hit::
0162
0163 # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \
0164 /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
0165
0166 # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
0167 /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
0168
0169 # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
0170 /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
0171
0172 The above sets up an initially paused hist trigger which is unpaused
0173 and starts aggregating events when a given program is executed, and
0174 which stops aggregating when the process exits and the hist trigger
0175 is paused again.
0176
0177 The examples below provide a more concrete illustration of the
0178 concepts and typical usage patterns discussed above.
0179
0180 'special' event fields
0181 ------------------------
0182
0183 There are a number of 'special event fields' available for use as
0184 keys or values in a hist trigger. These look like and behave as if
0185 they were actual event fields, but aren't really part of the event's
0186 field definition or format file. They are however available for any
0187 event, and can be used anywhere an actual event field could be.
0188 They are:
0189
0190 ====================== ==== =======================================
0191 common_timestamp u64 timestamp (from ring buffer) associated
0192 with the event, in nanoseconds. May be
0193 modified by .usecs to have timestamps
0194 interpreted as microseconds.
0195 common_cpu int the cpu on which the event occurred.
0196 ====================== ==== =======================================
0197
0198 Extended error information
0199 --------------------------
0200
0201 For some error conditions encountered when invoking a hist trigger
0202 command, extended error information is available via the
0203 tracing/error_log file. See Error Conditions in
0204 :file:`Documentation/trace/ftrace.rst` for details.
0205
0206 6.2 'hist' trigger examples
0207 ---------------------------
0208
0209 The first set of examples creates aggregations using the kmalloc
0210 event. The fields that can be used for the hist trigger are listed
0211 in the kmalloc event's format file::
0212
0213 # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/format
0214 name: kmalloc
0215 ID: 374
0216 format:
0217 field:unsigned short common_type; offset:0; size:2; signed:0;
0218 field:unsigned char common_flags; offset:2; size:1; signed:0;
0219 field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
0220 field:int common_pid; offset:4; size:4; signed:1;
0221
0222 field:unsigned long call_site; offset:8; size:8; signed:0;
0223 field:const void * ptr; offset:16; size:8; signed:0;
0224 field:size_t bytes_req; offset:24; size:8; signed:0;
0225 field:size_t bytes_alloc; offset:32; size:8; signed:0;
0226 field:gfp_t gfp_flags; offset:40; size:4; signed:0;
0227
0228 We'll start by creating a hist trigger that generates a simple table
0229 that lists the total number of bytes requested for each function in
0230 the kernel that made one or more calls to kmalloc::
0231
0232 # echo 'hist:key=call_site:val=bytes_req.buckets=32' > \
0233 /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
0234
0235 This tells the tracing system to create a 'hist' trigger using the
0236 call_site field of the kmalloc event as the key for the table, which
0237 just means that each unique call_site address will have an entry
0238 created for it in the table. The 'val=bytes_req' parameter tells
0239 the hist trigger that for each unique entry (call_site) in the
0240 table, it should keep a running total of the number of bytes
0241 requested by that call_site.
0242
0243 We'll let it run for awhile and then dump the contents of the 'hist'
0244 file in the kmalloc event's subdirectory (for readability, a number
0245 of entries have been omitted)::
0246
0247 # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
0248 # trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
0249
0250 { call_site: 18446744072106379007 } hitcount: 1 bytes_req: 176
0251 { call_site: 18446744071579557049 } hitcount: 1 bytes_req: 1024
0252 { call_site: 18446744071580608289 } hitcount: 1 bytes_req: 16384
0253 { call_site: 18446744071581827654 } hitcount: 1 bytes_req: 24
0254 { call_site: 18446744071580700980 } hitcount: 1 bytes_req: 8
0255 { call_site: 18446744071579359876 } hitcount: 1 bytes_req: 152
0256 { call_site: 18446744071580795365 } hitcount: 3 bytes_req: 144
0257 { call_site: 18446744071581303129 } hitcount: 3 bytes_req: 144
0258 { call_site: 18446744071580713234 } hitcount: 4 bytes_req: 2560
0259 { call_site: 18446744071580933750 } hitcount: 4 bytes_req: 736
0260 .
0261 .
0262 .
0263 { call_site: 18446744072106047046 } hitcount: 69 bytes_req: 5576
0264 { call_site: 18446744071582116407 } hitcount: 73 bytes_req: 2336
0265 { call_site: 18446744072106054684 } hitcount: 136 bytes_req: 140504
0266 { call_site: 18446744072106224230 } hitcount: 136 bytes_req: 19584
0267 { call_site: 18446744072106078074 } hitcount: 153 bytes_req: 2448
0268 { call_site: 18446744072106062406 } hitcount: 153 bytes_req: 36720
0269 { call_site: 18446744071582507929 } hitcount: 153 bytes_req: 37088
0270 { call_site: 18446744072102520590 } hitcount: 273 bytes_req: 10920
0271 { call_site: 18446744071582143559 } hitcount: 358 bytes_req: 716
0272 { call_site: 18446744072106465852 } hitcount: 417 bytes_req: 56712
0273 { call_site: 18446744072102523378 } hitcount: 485 bytes_req: 27160
0274 { call_site: 18446744072099568646 } hitcount: 1676 bytes_req: 33520
0275
0276 Totals:
0277 Hits: 4610
0278 Entries: 45
0279 Dropped: 0
0280
0281 The output displays a line for each entry, beginning with the key
0282 specified in the trigger, followed by the value(s) also specified in
0283 the trigger. At the beginning of the output is a line that displays
0284 the trigger info, which can also be displayed by reading the
0285 'trigger' file::
0286
0287 # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
0288 hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
0289
0290 At the end of the output are a few lines that display the overall
0291 totals for the run. The 'Hits' field shows the total number of
0292 times the event trigger was hit, the 'Entries' field shows the total
0293 number of used entries in the hash table, and the 'Dropped' field
0294 shows the number of hits that were dropped because the number of
0295 used entries for the run exceeded the maximum number of entries
0296 allowed for the table (normally 0, but if not a hint that you may
0297 want to increase the size of the table using the 'size' parameter).
0298
0299 Notice in the above output that there's an extra field, 'hitcount',
0300 which wasn't specified in the trigger. Also notice that in the
0301 trigger info output, there's a parameter, 'sort=hitcount', which
0302 wasn't specified in the trigger either. The reason for that is that
0303 every trigger implicitly keeps a count of the total number of hits
0304 attributed to a given entry, called the 'hitcount'. That hitcount
0305 information is explicitly displayed in the output, and in the
0306 absence of a user-specified sort parameter, is used as the default
0307 sort field.
0308
0309 The value 'hitcount' can be used in place of an explicit value in
0310 the 'values' parameter if you don't really need to have any
0311 particular field summed and are mainly interested in hit
0312 frequencies.
0313
0314 To turn the hist trigger off, simply call up the trigger in the
0315 command history and re-execute it with a '!' prepended::
0316
0317 # echo '!hist:key=call_site:val=bytes_req' > \
0318 /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
0319
0320 Finally, notice that the call_site as displayed in the output above
0321 isn't really very useful. It's an address, but normally addresses
0322 are displayed in hex. To have a numeric field displayed as a hex
0323 value, simply append '.hex' to the field name in the trigger::
0324
0325 # echo 'hist:key=call_site.hex:val=bytes_req' > \
0326 /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
0327
0328 # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
0329 # trigger info: hist:keys=call_site.hex:vals=bytes_req:sort=hitcount:size=2048 [active]
0330
0331 { call_site: ffffffffa026b291 } hitcount: 1 bytes_req: 433
0332 { call_site: ffffffffa07186ff } hitcount: 1 bytes_req: 176
0333 { call_site: ffffffff811ae721 } hitcount: 1 bytes_req: 16384
0334 { call_site: ffffffff811c5134 } hitcount: 1 bytes_req: 8
0335 { call_site: ffffffffa04a9ebb } hitcount: 1 bytes_req: 511
0336 { call_site: ffffffff8122e0a6 } hitcount: 1 bytes_req: 12
0337 { call_site: ffffffff8107da84 } hitcount: 1 bytes_req: 152
0338 { call_site: ffffffff812d8246 } hitcount: 1 bytes_req: 24
0339 { call_site: ffffffff811dc1e5 } hitcount: 3 bytes_req: 144
0340 { call_site: ffffffffa02515e8 } hitcount: 3 bytes_req: 648
0341 { call_site: ffffffff81258159 } hitcount: 3 bytes_req: 144
0342 { call_site: ffffffff811c80f4 } hitcount: 4 bytes_req: 544
0343 .
0344 .
0345 .
0346 { call_site: ffffffffa06c7646 } hitcount: 106 bytes_req: 8024
0347 { call_site: ffffffffa06cb246 } hitcount: 132 bytes_req: 31680
0348 { call_site: ffffffffa06cef7a } hitcount: 132 bytes_req: 2112
0349 { call_site: ffffffff8137e399 } hitcount: 132 bytes_req: 23232
0350 { call_site: ffffffffa06c941c } hitcount: 185 bytes_req: 171360
0351 { call_site: ffffffffa06f2a66 } hitcount: 185 bytes_req: 26640
0352 { call_site: ffffffffa036a70e } hitcount: 265 bytes_req: 10600
0353 { call_site: ffffffff81325447 } hitcount: 292 bytes_req: 584
0354 { call_site: ffffffffa072da3c } hitcount: 446 bytes_req: 60656
0355 { call_site: ffffffffa036b1f2 } hitcount: 526 bytes_req: 29456
0356 { call_site: ffffffffa0099c06 } hitcount: 1780 bytes_req: 35600
0357
0358 Totals:
0359 Hits: 4775
0360 Entries: 46
0361 Dropped: 0
0362
0363 Even that's only marginally more useful - while hex values do look
0364 more like addresses, what users are typically more interested in
0365 when looking at text addresses are the corresponding symbols
0366 instead. To have an address displayed as symbolic value instead,
0367 simply append '.sym' or '.sym-offset' to the field name in the
0368 trigger::
0369
0370 # echo 'hist:key=call_site.sym:val=bytes_req' > \
0371 /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
0372
0373 # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
0374 # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=hitcount:size=2048 [active]
0375
0376 { call_site: [ffffffff810adcb9] syslog_print_all } hitcount: 1 bytes_req: 1024
0377 { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
0378 { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
0379 { call_site: [ffffffff8154acbe] usb_alloc_urb } hitcount: 1 bytes_req: 192
0380 { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
0381 { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
0382 { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
0383 { call_site: [ffffffff811febd5] fsnotify_alloc_group } hitcount: 2 bytes_req: 528
0384 { call_site: [ffffffff81440f58] __tty_buffer_request_room } hitcount: 2 bytes_req: 2624
0385 { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 2 bytes_req: 96
0386 { call_site: [ffffffffa05e19af] ieee80211_start_tx_ba_session [mac80211] } hitcount: 2 bytes_req: 464
0387 { call_site: [ffffffff81672406] tcp_get_metrics } hitcount: 2 bytes_req: 304
0388 { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
0389 { call_site: [ffffffff81089b05] sched_create_group } hitcount: 2 bytes_req: 1424
0390 .
0391 .
0392 .
0393 { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1185 bytes_req: 123240
0394 { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 1185 bytes_req: 104280
0395 { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 1402 bytes_req: 190672
0396 { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 1518 bytes_req: 146208
0397 { call_site: [ffffffffa029070e] drm_vma_node_allow [drm] } hitcount: 1746 bytes_req: 69840
0398 { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 2021 bytes_req: 792312
0399 { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 2592 bytes_req: 145152
0400 { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2629 bytes_req: 378576
0401 { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2629 bytes_req: 3783248
0402 { call_site: [ffffffff81325607] apparmor_file_alloc_security } hitcount: 5192 bytes_req: 10384
0403 { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 5529 bytes_req: 110584
0404 { call_site: [ffffffff8131ebf7] aa_alloc_task_context } hitcount: 21943 bytes_req: 702176
0405 { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 55759 bytes_req: 5074265
0406
0407 Totals:
0408 Hits: 109928
0409 Entries: 71
0410 Dropped: 0
0411
0412 Because the default sort key above is 'hitcount', the above shows a
0413 the list of call_sites by increasing hitcount, so that at the bottom
0414 we see the functions that made the most kmalloc calls during the
0415 run. If instead we we wanted to see the top kmalloc callers in
0416 terms of the number of bytes requested rather than the number of
0417 calls, and we wanted the top caller to appear at the top, we can use
0418 the 'sort' parameter, along with the 'descending' modifier::
0419
0420 # echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \
0421 /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
0422
0423 # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
0424 # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
0425
0426 { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2186 bytes_req: 3397464
0427 { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1790 bytes_req: 712176
0428 { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 8132 bytes_req: 513135
0429 { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 106 bytes_req: 440128
0430 { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2186 bytes_req: 314784
0431 { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 2174 bytes_req: 208992
0432 { call_site: [ffffffff811ae8e1] __kmalloc } hitcount: 8 bytes_req: 131072
0433 { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 859 bytes_req: 116824
0434 { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 1834 bytes_req: 102704
0435 { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 972 bytes_req: 101088
0436 { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 972 bytes_req: 85536
0437 { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 3333 bytes_req: 66664
0438 { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 209 bytes_req: 61632
0439 .
0440 .
0441 .
0442 { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
0443 { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
0444 { call_site: [ffffffff812d8406] copy_semundo } hitcount: 2 bytes_req: 48
0445 { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 1 bytes_req: 48
0446 { call_site: [ffffffffa027121a] drm_getmagic [drm] } hitcount: 1 bytes_req: 48
0447 { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
0448 { call_site: [ffffffff811c52f4] bprm_change_interp } hitcount: 2 bytes_req: 16
0449 { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
0450 { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
0451 { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
0452
0453 Totals:
0454 Hits: 32133
0455 Entries: 81
0456 Dropped: 0
0457
0458 To display the offset and size information in addition to the symbol
0459 name, just use 'sym-offset' instead::
0460
0461 # echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \
0462 /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
0463
0464 # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
0465 # trigger info: hist:keys=call_site.sym-offset:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
0466
0467 { call_site: [ffffffffa046041c] i915_gem_execbuffer2+0x6c/0x2c0 [i915] } hitcount: 4569 bytes_req: 3163720
0468 { call_site: [ffffffffa0489a66] intel_ring_begin+0xc6/0x1f0 [i915] } hitcount: 4569 bytes_req: 657936
0469 { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23+0x694/0x1020 [i915] } hitcount: 1519 bytes_req: 472936
0470 { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23+0x516/0x1020 [i915] } hitcount: 3050 bytes_req: 211832
0471 { call_site: [ffffffff811e2a1b] seq_buf_alloc+0x1b/0x50 } hitcount: 34 bytes_req: 148384
0472 { call_site: [ffffffffa04a580c] intel_crtc_page_flip+0xbc/0x870 [i915] } hitcount: 1385 bytes_req: 144040
0473 { call_site: [ffffffff811ae8e1] __kmalloc+0x191/0x1b0 } hitcount: 8 bytes_req: 131072
0474 { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl+0x282/0x360 [drm] } hitcount: 1385 bytes_req: 121880
0475 { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc+0x32/0x100 [drm] } hitcount: 1848 bytes_req: 103488
0476 { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state+0x2c/0xa0 [i915] } hitcount: 461 bytes_req: 62696
0477 { call_site: [ffffffffa029070e] drm_vma_node_allow+0x2e/0xd0 [drm] } hitcount: 1541 bytes_req: 61640
0478 { call_site: [ffffffff815f8d7b] sk_prot_alloc+0xcb/0x1b0 } hitcount: 57 bytes_req: 57456
0479 .
0480 .
0481 .
0482 { call_site: [ffffffff8109524a] alloc_fair_sched_group+0x5a/0x1a0 } hitcount: 2 bytes_req: 128
0483 { call_site: [ffffffffa027b921] drm_vm_open_locked+0x31/0xa0 [drm] } hitcount: 3 bytes_req: 96
0484 { call_site: [ffffffff8122e266] proc_self_follow_link+0x76/0xb0 } hitcount: 8 bytes_req: 96
0485 { call_site: [ffffffff81213e80] load_elf_binary+0x240/0x1650 } hitcount: 3 bytes_req: 84
0486 { call_site: [ffffffff8154bc62] usb_control_msg+0x42/0x110 } hitcount: 1 bytes_req: 8
0487 { call_site: [ffffffffa00bf6fe] hidraw_send_report+0x7e/0x1a0 [hid] } hitcount: 1 bytes_req: 7
0488 { call_site: [ffffffffa00bf1ca] hidraw_report_event+0x8a/0x120 [hid] } hitcount: 1 bytes_req: 7
0489
0490 Totals:
0491 Hits: 26098
0492 Entries: 64
0493 Dropped: 0
0494
0495 We can also add multiple fields to the 'values' parameter. For
0496 example, we might want to see the total number of bytes allocated
0497 alongside bytes requested, and display the result sorted by bytes
0498 allocated in a descending order::
0499
0500 # echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \
0501 /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
0502
0503 # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
0504 # trigger info: hist:keys=call_site.sym:vals=bytes_req,bytes_alloc:sort=bytes_alloc.descending:size=2048 [active]
0505
0506 { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 7403 bytes_req: 4084360 bytes_alloc: 5958016
0507 { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 541 bytes_req: 2213968 bytes_alloc: 2228224
0508 { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 7404 bytes_req: 1066176 bytes_alloc: 1421568
0509 { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1565 bytes_req: 557368 bytes_alloc: 1037760
0510 { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 9557 bytes_req: 595778 bytes_alloc: 695744
0511 { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 5839 bytes_req: 430680 bytes_alloc: 470400
0512 { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 2388 bytes_req: 324768 bytes_alloc: 458496
0513 { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 3911 bytes_req: 219016 bytes_alloc: 250304
0514 { call_site: [ffffffff815f8d7b] sk_prot_alloc } hitcount: 235 bytes_req: 236880 bytes_alloc: 240640
0515 { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 557 bytes_req: 169024 bytes_alloc: 221760
0516 { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 9378 bytes_req: 187548 bytes_alloc: 206312
0517 { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1519 bytes_req: 157976 bytes_alloc: 194432
0518 .
0519 .
0520 .
0521 { call_site: [ffffffff8109bd3b] sched_autogroup_create_attach } hitcount: 2 bytes_req: 144 bytes_alloc: 192
0522 { call_site: [ffffffff81097ee8] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
0523 { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
0524 { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
0525 { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
0526 { call_site: [ffffffff81213e80] load_elf_binary } hitcount: 3 bytes_req: 84 bytes_alloc: 96
0527 { call_site: [ffffffff81079a2e] kthread_create_on_node } hitcount: 1 bytes_req: 56 bytes_alloc: 64
0528 { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
0529 { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 bytes_alloc: 8
0530 { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
0531
0532 Totals:
0533 Hits: 66598
0534 Entries: 65
0535 Dropped: 0
0536
0537 Finally, to finish off our kmalloc example, instead of simply having
0538 the hist trigger display symbolic call_sites, we can have the hist
0539 trigger additionally display the complete set of kernel stack traces
0540 that led to each call_site. To do that, we simply use the special
0541 value 'stacktrace' for the key parameter::
0542
0543 # echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \
0544 /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
0545
0546 The above trigger will use the kernel stack trace in effect when an
0547 event is triggered as the key for the hash table. This allows the
0548 enumeration of every kernel callpath that led up to a particular
0549 event, along with a running total of any of the event fields for
0550 that event. Here we tally bytes requested and bytes allocated for
0551 every callpath in the system that led up to a kmalloc (in this case
0552 every callpath to a kmalloc for a kernel compile)::
0553
0554 # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
0555 # trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active]
0556
0557 { stacktrace:
0558 __kmalloc_track_caller+0x10b/0x1a0
0559 kmemdup+0x20/0x50
0560 hidraw_report_event+0x8a/0x120 [hid]
0561 hid_report_raw_event+0x3ea/0x440 [hid]
0562 hid_input_report+0x112/0x190 [hid]
0563 hid_irq_in+0xc2/0x260 [usbhid]
0564 __usb_hcd_giveback_urb+0x72/0x120
0565 usb_giveback_urb_bh+0x9e/0xe0
0566 tasklet_hi_action+0xf8/0x100
0567 __do_softirq+0x114/0x2c0
0568 irq_exit+0xa5/0xb0
0569 do_IRQ+0x5a/0xf0
0570 ret_from_intr+0x0/0x30
0571 cpuidle_enter+0x17/0x20
0572 cpu_startup_entry+0x315/0x3e0
0573 rest_init+0x7c/0x80
0574 } hitcount: 3 bytes_req: 21 bytes_alloc: 24
0575 { stacktrace:
0576 __kmalloc_track_caller+0x10b/0x1a0
0577 kmemdup+0x20/0x50
0578 hidraw_report_event+0x8a/0x120 [hid]
0579 hid_report_raw_event+0x3ea/0x440 [hid]
0580 hid_input_report+0x112/0x190 [hid]
0581 hid_irq_in+0xc2/0x260 [usbhid]
0582 __usb_hcd_giveback_urb+0x72/0x120
0583 usb_giveback_urb_bh+0x9e/0xe0
0584 tasklet_hi_action+0xf8/0x100
0585 __do_softirq+0x114/0x2c0
0586 irq_exit+0xa5/0xb0
0587 do_IRQ+0x5a/0xf0
0588 ret_from_intr+0x0/0x30
0589 } hitcount: 3 bytes_req: 21 bytes_alloc: 24
0590 { stacktrace:
0591 kmem_cache_alloc_trace+0xeb/0x150
0592 aa_alloc_task_context+0x27/0x40
0593 apparmor_cred_prepare+0x1f/0x50
0594 security_prepare_creds+0x16/0x20
0595 prepare_creds+0xdf/0x1a0
0596 SyS_capset+0xb5/0x200
0597 system_call_fastpath+0x12/0x6a
0598 } hitcount: 1 bytes_req: 32 bytes_alloc: 32
0599 .
0600 .
0601 .
0602 { stacktrace:
0603 __kmalloc+0x11b/0x1b0
0604 i915_gem_execbuffer2+0x6c/0x2c0 [i915]
0605 drm_ioctl+0x349/0x670 [drm]
0606 do_vfs_ioctl+0x2f0/0x4f0
0607 SyS_ioctl+0x81/0xa0
0608 system_call_fastpath+0x12/0x6a
0609 } hitcount: 17726 bytes_req: 13944120 bytes_alloc: 19593808
0610 { stacktrace:
0611 __kmalloc+0x11b/0x1b0
0612 load_elf_phdrs+0x76/0xa0
0613 load_elf_binary+0x102/0x1650
0614 search_binary_handler+0x97/0x1d0
0615 do_execveat_common.isra.34+0x551/0x6e0
0616 SyS_execve+0x3a/0x50
0617 return_from_execve+0x0/0x23
0618 } hitcount: 33348 bytes_req: 17152128 bytes_alloc: 20226048
0619 { stacktrace:
0620 kmem_cache_alloc_trace+0xeb/0x150
0621 apparmor_file_alloc_security+0x27/0x40
0622 security_file_alloc+0x16/0x20
0623 get_empty_filp+0x93/0x1c0
0624 path_openat+0x31/0x5f0
0625 do_filp_open+0x3a/0x90
0626 do_sys_open+0x128/0x220
0627 SyS_open+0x1e/0x20
0628 system_call_fastpath+0x12/0x6a
0629 } hitcount: 4766422 bytes_req: 9532844 bytes_alloc: 38131376
0630 { stacktrace:
0631 __kmalloc+0x11b/0x1b0
0632 seq_buf_alloc+0x1b/0x50
0633 seq_read+0x2cc/0x370
0634 proc_reg_read+0x3d/0x80
0635 __vfs_read+0x28/0xe0
0636 vfs_read+0x86/0x140
0637 SyS_read+0x46/0xb0
0638 system_call_fastpath+0x12/0x6a
0639 } hitcount: 19133 bytes_req: 78368768 bytes_alloc: 78368768
0640
0641 Totals:
0642 Hits: 6085872
0643 Entries: 253
0644 Dropped: 0
0645
0646 If you key a hist trigger on common_pid, in order for example to
0647 gather and display sorted totals for each process, you can use the
0648 special .execname modifier to display the executable names for the
0649 processes in the table rather than raw pids. The example below
0650 keeps a per-process sum of total bytes read::
0651
0652 # echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \
0653 /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
0654
0655 # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/hist
0656 # trigger info: hist:keys=common_pid.execname:vals=count:sort=count.descending:size=2048 [active]
0657
0658 { common_pid: gnome-terminal [ 3196] } hitcount: 280 count: 1093512
0659 { common_pid: Xorg [ 1309] } hitcount: 525 count: 256640
0660 { common_pid: compiz [ 2889] } hitcount: 59 count: 254400
0661 { common_pid: bash [ 8710] } hitcount: 3 count: 66369
0662 { common_pid: dbus-daemon-lau [ 8703] } hitcount: 49 count: 47739
0663 { common_pid: irqbalance [ 1252] } hitcount: 27 count: 27648
0664 { common_pid: 01ifupdown [ 8705] } hitcount: 3 count: 17216
0665 { common_pid: dbus-daemon [ 772] } hitcount: 10 count: 12396
0666 { common_pid: Socket Thread [ 8342] } hitcount: 11 count: 11264
0667 { common_pid: nm-dhcp-client. [ 8701] } hitcount: 6 count: 7424
0668 { common_pid: gmain [ 1315] } hitcount: 18 count: 6336
0669 .
0670 .
0671 .
0672 { common_pid: postgres [ 1892] } hitcount: 2 count: 32
0673 { common_pid: postgres [ 1891] } hitcount: 2 count: 32
0674 { common_pid: gmain [ 8704] } hitcount: 2 count: 32
0675 { common_pid: upstart-dbus-br [ 2740] } hitcount: 21 count: 21
0676 { common_pid: nm-dispatcher.a [ 8696] } hitcount: 1 count: 16
0677 { common_pid: indicator-datet [ 2904] } hitcount: 1 count: 16
0678 { common_pid: gdbus [ 2998] } hitcount: 1 count: 16
0679 { common_pid: rtkit-daemon [ 2052] } hitcount: 1 count: 8
0680 { common_pid: init [ 1] } hitcount: 2 count: 2
0681
0682 Totals:
0683 Hits: 2116
0684 Entries: 51
0685 Dropped: 0
0686
0687 Similarly, if you key a hist trigger on syscall id, for example to
0688 gather and display a list of systemwide syscall hits, you can use
0689 the special .syscall modifier to display the syscall names rather
0690 than raw ids. The example below keeps a running total of syscall
0691 counts for the system during the run::
0692
0693 # echo 'hist:key=id.syscall:val=hitcount' > \
0694 /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
0695
0696 # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
0697 # trigger info: hist:keys=id.syscall:vals=hitcount:sort=hitcount:size=2048 [active]
0698
0699 { id: sys_fsync [ 74] } hitcount: 1
0700 { id: sys_newuname [ 63] } hitcount: 1
0701 { id: sys_prctl [157] } hitcount: 1
0702 { id: sys_statfs [137] } hitcount: 1
0703 { id: sys_symlink [ 88] } hitcount: 1
0704 { id: sys_sendmmsg [307] } hitcount: 1
0705 { id: sys_semctl [ 66] } hitcount: 1
0706 { id: sys_readlink [ 89] } hitcount: 3
0707 { id: sys_bind [ 49] } hitcount: 3
0708 { id: sys_getsockname [ 51] } hitcount: 3
0709 { id: sys_unlink [ 87] } hitcount: 3
0710 { id: sys_rename [ 82] } hitcount: 4
0711 { id: unknown_syscall [ 58] } hitcount: 4
0712 { id: sys_connect [ 42] } hitcount: 4
0713 { id: sys_getpid [ 39] } hitcount: 4
0714 .
0715 .
0716 .
0717 { id: sys_rt_sigprocmask [ 14] } hitcount: 952
0718 { id: sys_futex [202] } hitcount: 1534
0719 { id: sys_write [ 1] } hitcount: 2689
0720 { id: sys_setitimer [ 38] } hitcount: 2797
0721 { id: sys_read [ 0] } hitcount: 3202
0722 { id: sys_select [ 23] } hitcount: 3773
0723 { id: sys_writev [ 20] } hitcount: 4531
0724 { id: sys_poll [ 7] } hitcount: 8314
0725 { id: sys_recvmsg [ 47] } hitcount: 13738
0726 { id: sys_ioctl [ 16] } hitcount: 21843
0727
0728 Totals:
0729 Hits: 67612
0730 Entries: 72
0731 Dropped: 0
0732
0733 The syscall counts above provide a rough overall picture of system
0734 call activity on the system; we can see for example that the most
0735 popular system call on this system was the 'sys_ioctl' system call.
0736
0737 We can use 'compound' keys to refine that number and provide some
0738 further insight as to which processes exactly contribute to the
0739 overall ioctl count.
0740
0741 The command below keeps a hitcount for every unique combination of
0742 system call id and pid - the end result is essentially a table
0743 that keeps a per-pid sum of system call hits. The results are
0744 sorted using the system call id as the primary key, and the
0745 hitcount sum as the secondary key::
0746
0747 # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \
0748 /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
0749
0750 # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
0751 # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active]
0752
0753 { id: sys_read [ 0], common_pid: rtkit-daemon [ 1877] } hitcount: 1
0754 { id: sys_read [ 0], common_pid: gdbus [ 2976] } hitcount: 1
0755 { id: sys_read [ 0], common_pid: console-kit-dae [ 3400] } hitcount: 1
0756 { id: sys_read [ 0], common_pid: postgres [ 1865] } hitcount: 1
0757 { id: sys_read [ 0], common_pid: deja-dup-monito [ 3543] } hitcount: 2
0758 { id: sys_read [ 0], common_pid: NetworkManager [ 890] } hitcount: 2
0759 { id: sys_read [ 0], common_pid: evolution-calen [ 3048] } hitcount: 2
0760 { id: sys_read [ 0], common_pid: postgres [ 1864] } hitcount: 2
0761 { id: sys_read [ 0], common_pid: nm-applet [ 3022] } hitcount: 2
0762 { id: sys_read [ 0], common_pid: whoopsie [ 1212] } hitcount: 2
0763 .
0764 .
0765 .
0766 { id: sys_ioctl [ 16], common_pid: bash [ 8479] } hitcount: 1
0767 { id: sys_ioctl [ 16], common_pid: bash [ 3472] } hitcount: 12
0768 { id: sys_ioctl [ 16], common_pid: gnome-terminal [ 3199] } hitcount: 16
0769 { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 1808
0770 { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 5580
0771 .
0772 .
0773 .
0774 { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2690] } hitcount: 3
0775 { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2688] } hitcount: 16
0776 { id: sys_inotify_add_watch [254], common_pid: gmain [ 975] } hitcount: 2
0777 { id: sys_inotify_add_watch [254], common_pid: gmain [ 3204] } hitcount: 4
0778 { id: sys_inotify_add_watch [254], common_pid: gmain [ 2888] } hitcount: 4
0779 { id: sys_inotify_add_watch [254], common_pid: gmain [ 3003] } hitcount: 4
0780 { id: sys_inotify_add_watch [254], common_pid: gmain [ 2873] } hitcount: 4
0781 { id: sys_inotify_add_watch [254], common_pid: gmain [ 3196] } hitcount: 6
0782 { id: sys_openat [257], common_pid: java [ 2623] } hitcount: 2
0783 { id: sys_eventfd2 [290], common_pid: ibus-ui-gtk3 [ 2760] } hitcount: 4
0784 { id: sys_eventfd2 [290], common_pid: compiz [ 2994] } hitcount: 6
0785
0786 Totals:
0787 Hits: 31536
0788 Entries: 323
0789 Dropped: 0
0790
0791 The above list does give us a breakdown of the ioctl syscall by
0792 pid, but it also gives us quite a bit more than that, which we
0793 don't really care about at the moment. Since we know the syscall
0794 id for sys_ioctl (16, displayed next to the sys_ioctl name), we
0795 can use that to filter out all the other syscalls::
0796
0797 # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \
0798 /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
0799
0800 # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
0801 # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active]
0802
0803 { id: sys_ioctl [ 16], common_pid: gmain [ 2769] } hitcount: 1
0804 { id: sys_ioctl [ 16], common_pid: evolution-addre [ 8571] } hitcount: 1
0805 { id: sys_ioctl [ 16], common_pid: gmain [ 3003] } hitcount: 1
0806 { id: sys_ioctl [ 16], common_pid: gmain [ 2781] } hitcount: 1
0807 { id: sys_ioctl [ 16], common_pid: gmain [ 2829] } hitcount: 1
0808 { id: sys_ioctl [ 16], common_pid: bash [ 8726] } hitcount: 1
0809 { id: sys_ioctl [ 16], common_pid: bash [ 8508] } hitcount: 1
0810 { id: sys_ioctl [ 16], common_pid: gmain [ 2970] } hitcount: 1
0811 { id: sys_ioctl [ 16], common_pid: gmain [ 2768] } hitcount: 1
0812 .
0813 .
0814 .
0815 { id: sys_ioctl [ 16], common_pid: pool [ 8559] } hitcount: 45
0816 { id: sys_ioctl [ 16], common_pid: pool [ 8555] } hitcount: 48
0817 { id: sys_ioctl [ 16], common_pid: pool [ 8551] } hitcount: 48
0818 { id: sys_ioctl [ 16], common_pid: avahi-daemon [ 896] } hitcount: 66
0819 { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 26674
0820 { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 73443
0821
0822 Totals:
0823 Hits: 101162
0824 Entries: 103
0825 Dropped: 0
0826
0827 The above output shows that 'compiz' and 'Xorg' are far and away
0828 the heaviest ioctl callers (which might lead to questions about
0829 whether they really need to be making all those calls and to
0830 possible avenues for further investigation.)
0831
0832 The compound key examples used a key and a sum value (hitcount) to
0833 sort the output, but we can just as easily use two keys instead.
0834 Here's an example where we use a compound key composed of the the
0835 common_pid and size event fields. Sorting with pid as the primary
0836 key and 'size' as the secondary key allows us to display an
0837 ordered summary of the recvfrom sizes, with counts, received by
0838 each process::
0839
0840 # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \
0841 /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger
0842
0843 # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist
0844 # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active]
0845
0846 { common_pid: smbd [ 784], size: 4 } hitcount: 1
0847 { common_pid: dnsmasq [ 1412], size: 4096 } hitcount: 672
0848 { common_pid: postgres [ 1796], size: 1000 } hitcount: 6
0849 { common_pid: postgres [ 1867], size: 1000 } hitcount: 10
0850 { common_pid: bamfdaemon [ 2787], size: 28 } hitcount: 2
0851 { common_pid: bamfdaemon [ 2787], size: 14360 } hitcount: 1
0852 { common_pid: compiz [ 2994], size: 8 } hitcount: 1
0853 { common_pid: compiz [ 2994], size: 20 } hitcount: 11
0854 { common_pid: gnome-terminal [ 3199], size: 4 } hitcount: 2
0855 { common_pid: firefox [ 8817], size: 4 } hitcount: 1
0856 { common_pid: firefox [ 8817], size: 8 } hitcount: 5
0857 { common_pid: firefox [ 8817], size: 588 } hitcount: 2
0858 { common_pid: firefox [ 8817], size: 628 } hitcount: 1
0859 { common_pid: firefox [ 8817], size: 6944 } hitcount: 1
0860 { common_pid: firefox [ 8817], size: 408880 } hitcount: 2
0861 { common_pid: firefox [ 8822], size: 8 } hitcount: 2
0862 { common_pid: firefox [ 8822], size: 160 } hitcount: 2
0863 { common_pid: firefox [ 8822], size: 320 } hitcount: 2
0864 { common_pid: firefox [ 8822], size: 352 } hitcount: 1
0865 .
0866 .
0867 .
0868 { common_pid: pool [ 8923], size: 1960 } hitcount: 10
0869 { common_pid: pool [ 8923], size: 2048 } hitcount: 10
0870 { common_pid: pool [ 8924], size: 1960 } hitcount: 10
0871 { common_pid: pool [ 8924], size: 2048 } hitcount: 10
0872 { common_pid: pool [ 8928], size: 1964 } hitcount: 4
0873 { common_pid: pool [ 8928], size: 1965 } hitcount: 2
0874 { common_pid: pool [ 8928], size: 2048 } hitcount: 6
0875 { common_pid: pool [ 8929], size: 1982 } hitcount: 1
0876 { common_pid: pool [ 8929], size: 2048 } hitcount: 1
0877
0878 Totals:
0879 Hits: 2016
0880 Entries: 224
0881 Dropped: 0
0882
0883 The above example also illustrates the fact that although a compound
0884 key is treated as a single entity for hashing purposes, the sub-keys
0885 it's composed of can be accessed independently.
0886
0887 The next example uses a string field as the hash key and
0888 demonstrates how you can manually pause and continue a hist trigger.
0889 In this example, we'll aggregate fork counts and don't expect a
0890 large number of entries in the hash table, so we'll drop it to a
0891 much smaller number, say 256::
0892
0893 # echo 'hist:key=child_comm:val=hitcount:size=256' > \
0894 /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
0895
0896 # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
0897 # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
0898
0899 { child_comm: dconf worker } hitcount: 1
0900 { child_comm: ibus-daemon } hitcount: 1
0901 { child_comm: whoopsie } hitcount: 1
0902 { child_comm: smbd } hitcount: 1
0903 { child_comm: gdbus } hitcount: 1
0904 { child_comm: kthreadd } hitcount: 1
0905 { child_comm: dconf worker } hitcount: 1
0906 { child_comm: evolution-alarm } hitcount: 2
0907 { child_comm: Socket Thread } hitcount: 2
0908 { child_comm: postgres } hitcount: 2
0909 { child_comm: bash } hitcount: 3
0910 { child_comm: compiz } hitcount: 3
0911 { child_comm: evolution-sourc } hitcount: 4
0912 { child_comm: dhclient } hitcount: 4
0913 { child_comm: pool } hitcount: 5
0914 { child_comm: nm-dispatcher.a } hitcount: 8
0915 { child_comm: firefox } hitcount: 8
0916 { child_comm: dbus-daemon } hitcount: 8
0917 { child_comm: glib-pacrunner } hitcount: 10
0918 { child_comm: evolution } hitcount: 23
0919
0920 Totals:
0921 Hits: 89
0922 Entries: 20
0923 Dropped: 0
0924
0925 If we want to pause the hist trigger, we can simply append :pause to
0926 the command that started the trigger. Notice that the trigger info
0927 displays as [paused]::
0928
0929 # echo 'hist:key=child_comm:val=hitcount:size=256:pause' >> \
0930 /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
0931
0932 # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
0933 # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [paused]
0934
0935 { child_comm: dconf worker } hitcount: 1
0936 { child_comm: kthreadd } hitcount: 1
0937 { child_comm: dconf worker } hitcount: 1
0938 { child_comm: gdbus } hitcount: 1
0939 { child_comm: ibus-daemon } hitcount: 1
0940 { child_comm: Socket Thread } hitcount: 2
0941 { child_comm: evolution-alarm } hitcount: 2
0942 { child_comm: smbd } hitcount: 2
0943 { child_comm: bash } hitcount: 3
0944 { child_comm: whoopsie } hitcount: 3
0945 { child_comm: compiz } hitcount: 3
0946 { child_comm: evolution-sourc } hitcount: 4
0947 { child_comm: pool } hitcount: 5
0948 { child_comm: postgres } hitcount: 6
0949 { child_comm: firefox } hitcount: 8
0950 { child_comm: dhclient } hitcount: 10
0951 { child_comm: emacs } hitcount: 12
0952 { child_comm: dbus-daemon } hitcount: 20
0953 { child_comm: nm-dispatcher.a } hitcount: 20
0954 { child_comm: evolution } hitcount: 35
0955 { child_comm: glib-pacrunner } hitcount: 59
0956
0957 Totals:
0958 Hits: 199
0959 Entries: 21
0960 Dropped: 0
0961
0962 To manually continue having the trigger aggregate events, append
0963 :cont instead. Notice that the trigger info displays as [active]
0964 again, and the data has changed::
0965
0966 # echo 'hist:key=child_comm:val=hitcount:size=256:cont' >> \
0967 /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
0968
0969 # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
0970 # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
0971
0972 { child_comm: dconf worker } hitcount: 1
0973 { child_comm: dconf worker } hitcount: 1
0974 { child_comm: kthreadd } hitcount: 1
0975 { child_comm: gdbus } hitcount: 1
0976 { child_comm: ibus-daemon } hitcount: 1
0977 { child_comm: Socket Thread } hitcount: 2
0978 { child_comm: evolution-alarm } hitcount: 2
0979 { child_comm: smbd } hitcount: 2
0980 { child_comm: whoopsie } hitcount: 3
0981 { child_comm: compiz } hitcount: 3
0982 { child_comm: evolution-sourc } hitcount: 4
0983 { child_comm: bash } hitcount: 5
0984 { child_comm: pool } hitcount: 5
0985 { child_comm: postgres } hitcount: 6
0986 { child_comm: firefox } hitcount: 8
0987 { child_comm: dhclient } hitcount: 11
0988 { child_comm: emacs } hitcount: 12
0989 { child_comm: dbus-daemon } hitcount: 22
0990 { child_comm: nm-dispatcher.a } hitcount: 22
0991 { child_comm: evolution } hitcount: 35
0992 { child_comm: glib-pacrunner } hitcount: 59
0993
0994 Totals:
0995 Hits: 206
0996 Entries: 21
0997 Dropped: 0
0998
0999 The previous example showed how to start and stop a hist trigger by
1000 appending 'pause' and 'continue' to the hist trigger command. A
1001 hist trigger can also be started in a paused state by initially
1002 starting the trigger with ':pause' appended. This allows you to
1003 start the trigger only when you're ready to start collecting data
1004 and not before. For example, you could start the trigger in a
1005 paused state, then unpause it and do something you want to measure,
1006 then pause the trigger again when done.
1007
1008 Of course, doing this manually can be difficult and error-prone, but
1009 it is possible to automatically start and stop a hist trigger based
1010 on some condition, via the enable_hist and disable_hist triggers.
1011
1012 For example, suppose we wanted to take a look at the relative
1013 weights in terms of skb length for each callpath that leads to a
1014 netif_receive_skb event when downloading a decent-sized file using
1015 wget.
1016
1017 First we set up an initially paused stacktrace trigger on the
1018 netif_receive_skb event::
1019
1020 # echo 'hist:key=stacktrace:vals=len:pause' > \
1021 /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
1022
1023 Next, we set up an 'enable_hist' trigger on the sched_process_exec
1024 event, with an 'if filename==/usr/bin/wget' filter. The effect of
1025 this new trigger is that it will 'unpause' the hist trigger we just
1026 set up on netif_receive_skb if and only if it sees a
1027 sched_process_exec event with a filename of '/usr/bin/wget'. When
1028 that happens, all netif_receive_skb events are aggregated into a
1029 hash table keyed on stacktrace::
1030
1031 # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
1032 /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
1033
1034 The aggregation continues until the netif_receive_skb is paused
1035 again, which is what the following disable_hist event does by
1036 creating a similar setup on the sched_process_exit event, using the
1037 filter 'comm==wget'::
1038
1039 # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
1040 /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
1041
1042 Whenever a process exits and the comm field of the disable_hist
1043 trigger filter matches 'comm==wget', the netif_receive_skb hist
1044 trigger is disabled.
1045
1046 The overall effect is that netif_receive_skb events are aggregated
1047 into the hash table for only the duration of the wget. Executing a
1048 wget command and then listing the 'hist' file will display the
1049 output generated by the wget command::
1050
1051 $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
1052
1053 # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
1054 # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
1055
1056 { stacktrace:
1057 __netif_receive_skb_core+0x46d/0x990
1058 __netif_receive_skb+0x18/0x60
1059 netif_receive_skb_internal+0x23/0x90
1060 napi_gro_receive+0xc8/0x100
1061 ieee80211_deliver_skb+0xd6/0x270 [mac80211]
1062 ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
1063 ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
1064 ieee80211_rx+0x31d/0x900 [mac80211]
1065 iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
1066 iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
1067 iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
1068 irq_thread_fn+0x20/0x50
1069 irq_thread+0x11f/0x150
1070 kthread+0xd2/0xf0
1071 ret_from_fork+0x42/0x70
1072 } hitcount: 85 len: 28884
1073 { stacktrace:
1074 __netif_receive_skb_core+0x46d/0x990
1075 __netif_receive_skb+0x18/0x60
1076 netif_receive_skb_internal+0x23/0x90
1077 napi_gro_complete+0xa4/0xe0
1078 dev_gro_receive+0x23a/0x360
1079 napi_gro_receive+0x30/0x100
1080 ieee80211_deliver_skb+0xd6/0x270 [mac80211]
1081 ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
1082 ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
1083 ieee80211_rx+0x31d/0x900 [mac80211]
1084 iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
1085 iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
1086 iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
1087 irq_thread_fn+0x20/0x50
1088 irq_thread+0x11f/0x150
1089 kthread+0xd2/0xf0
1090 } hitcount: 98 len: 664329
1091 { stacktrace:
1092 __netif_receive_skb_core+0x46d/0x990
1093 __netif_receive_skb+0x18/0x60
1094 process_backlog+0xa8/0x150
1095 net_rx_action+0x15d/0x340
1096 __do_softirq+0x114/0x2c0
1097 do_softirq_own_stack+0x1c/0x30
1098 do_softirq+0x65/0x70
1099 __local_bh_enable_ip+0xb5/0xc0
1100 ip_finish_output+0x1f4/0x840
1101 ip_output+0x6b/0xc0
1102 ip_local_out_sk+0x31/0x40
1103 ip_send_skb+0x1a/0x50
1104 udp_send_skb+0x173/0x2a0
1105 udp_sendmsg+0x2bf/0x9f0
1106 inet_sendmsg+0x64/0xa0
1107 sock_sendmsg+0x3d/0x50
1108 } hitcount: 115 len: 13030
1109 { stacktrace:
1110 __netif_receive_skb_core+0x46d/0x990
1111 __netif_receive_skb+0x18/0x60
1112 netif_receive_skb_internal+0x23/0x90
1113 napi_gro_complete+0xa4/0xe0
1114 napi_gro_flush+0x6d/0x90
1115 iwl_pcie_irq_handler+0x92a/0x12f0 [iwlwifi]
1116 irq_thread_fn+0x20/0x50
1117 irq_thread+0x11f/0x150
1118 kthread+0xd2/0xf0
1119 ret_from_fork+0x42/0x70
1120 } hitcount: 934 len: 5512212
1121
1122 Totals:
1123 Hits: 1232
1124 Entries: 4
1125 Dropped: 0
1126
1127 The above shows all the netif_receive_skb callpaths and their total
1128 lengths for the duration of the wget command.
1129
1130 The 'clear' hist trigger param can be used to clear the hash table.
1131 Suppose we wanted to try another run of the previous example but
1132 this time also wanted to see the complete list of events that went
1133 into the histogram. In order to avoid having to set everything up
1134 again, we can just clear the histogram first::
1135
1136 # echo 'hist:key=stacktrace:vals=len:clear' >> \
1137 /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
1138
1139 Just to verify that it is in fact cleared, here's what we now see in
1140 the hist file::
1141
1142 # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
1143 # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
1144
1145 Totals:
1146 Hits: 0
1147 Entries: 0
1148 Dropped: 0
1149
1150 Since we want to see the detailed list of every netif_receive_skb
1151 event occurring during the new run, which are in fact the same
1152 events being aggregated into the hash table, we add some additional
1153 'enable_event' events to the triggering sched_process_exec and
1154 sched_process_exit events as such::
1155
1156 # echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \
1157 /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
1158
1159 # echo 'disable_event:net:netif_receive_skb if comm==wget' > \
1160 /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
1161
1162 If you read the trigger files for the sched_process_exec and
1163 sched_process_exit triggers, you should see two triggers for each:
1164 one enabling/disabling the hist aggregation and the other
1165 enabling/disabling the logging of events::
1166
1167 # cat /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
1168 enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
1169 enable_hist:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
1170
1171 # cat /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
1172 enable_event:net:netif_receive_skb:unlimited if comm==wget
1173 disable_hist:net:netif_receive_skb:unlimited if comm==wget
1174
1175 In other words, whenever either of the sched_process_exec or
1176 sched_process_exit events is hit and matches 'wget', it enables or
1177 disables both the histogram and the event log, and what you end up
1178 with is a hash table and set of events just covering the specified
1179 duration. Run the wget command again::
1180
1181 $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
1182
1183 Displaying the 'hist' file should show something similar to what you
1184 saw in the last run, but this time you should also see the
1185 individual events in the trace file::
1186
1187 # cat /sys/kernel/debug/tracing/trace
1188
1189 # tracer: nop
1190 #
1191 # entries-in-buffer/entries-written: 183/1426 #P:4
1192 #
1193 # _-----=> irqs-off
1194 # / _----=> need-resched
1195 # | / _---=> hardirq/softirq
1196 # || / _--=> preempt-depth
1197 # ||| / delay
1198 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
1199 # | | | |||| | |
1200 wget-15108 [000] ..s1 31769.606929: netif_receive_skb: dev=lo skbaddr=ffff88009c353100 len=60
1201 wget-15108 [000] ..s1 31769.606999: netif_receive_skb: dev=lo skbaddr=ffff88009c353200 len=60
1202 dnsmasq-1382 [000] ..s1 31769.677652: netif_receive_skb: dev=lo skbaddr=ffff88009c352b00 len=130
1203 dnsmasq-1382 [000] ..s1 31769.685917: netif_receive_skb: dev=lo skbaddr=ffff88009c352200 len=138
1204 ##### CPU 2 buffer started ####
1205 irq/29-iwlwifi-559 [002] ..s. 31772.031529: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433d00 len=2948
1206 irq/29-iwlwifi-559 [002] ..s. 31772.031572: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432200 len=1500
1207 irq/29-iwlwifi-559 [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948
1208 irq/29-iwlwifi-559 [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948
1209 irq/29-iwlwifi-559 [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500
1210 .
1211 .
1212 .
1213
1214 The following example demonstrates how multiple hist triggers can be
1215 attached to a given event. This capability can be useful for
1216 creating a set of different summaries derived from the same set of
1217 events, or for comparing the effects of different filters, among
1218 other things::
1219
1220 # echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \
1221 /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
1222 # echo 'hist:keys=skbaddr.hex:vals=len if len > 4096' >> \
1223 /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
1224 # echo 'hist:keys=skbaddr.hex:vals=len if len == 256' >> \
1225 /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
1226 # echo 'hist:keys=skbaddr.hex:vals=len' >> \
1227 /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
1228 # echo 'hist:keys=len:vals=common_preempt_count' >> \
1229 /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
1230
1231 The above set of commands create four triggers differing only in
1232 their filters, along with a completely different though fairly
1233 nonsensical trigger. Note that in order to append multiple hist
1234 triggers to the same file, you should use the '>>' operator to
1235 append them ('>' will also add the new hist trigger, but will remove
1236 any existing hist triggers beforehand).
1237
1238 Displaying the contents of the 'hist' file for the event shows the
1239 contents of all five histograms::
1240
1241 # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
1242
1243 # event histogram
1244 #
1245 # trigger info: hist:keys=len:vals=hitcount,common_preempt_count:sort=hitcount:size=2048 [active]
1246 #
1247
1248 { len: 176 } hitcount: 1 common_preempt_count: 0
1249 { len: 223 } hitcount: 1 common_preempt_count: 0
1250 { len: 4854 } hitcount: 1 common_preempt_count: 0
1251 { len: 395 } hitcount: 1 common_preempt_count: 0
1252 { len: 177 } hitcount: 1 common_preempt_count: 0
1253 { len: 446 } hitcount: 1 common_preempt_count: 0
1254 { len: 1601 } hitcount: 1 common_preempt_count: 0
1255 .
1256 .
1257 .
1258 { len: 1280 } hitcount: 66 common_preempt_count: 0
1259 { len: 116 } hitcount: 81 common_preempt_count: 40
1260 { len: 708 } hitcount: 112 common_preempt_count: 0
1261 { len: 46 } hitcount: 221 common_preempt_count: 0
1262 { len: 1264 } hitcount: 458 common_preempt_count: 0
1263
1264 Totals:
1265 Hits: 1428
1266 Entries: 147
1267 Dropped: 0
1268
1269
1270 # event histogram
1271 #
1272 # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
1273 #
1274
1275 { skbaddr: ffff8800baee5e00 } hitcount: 1 len: 130
1276 { skbaddr: ffff88005f3d5600 } hitcount: 1 len: 1280
1277 { skbaddr: ffff88005f3d4900 } hitcount: 1 len: 1280
1278 { skbaddr: ffff88009fed6300 } hitcount: 1 len: 115
1279 { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 115
1280 { skbaddr: ffff88008cdb1900 } hitcount: 1 len: 46
1281 { skbaddr: ffff880064b5ef00 } hitcount: 1 len: 118
1282 { skbaddr: ffff880044e3c700 } hitcount: 1 len: 60
1283 { skbaddr: ffff880100065900 } hitcount: 1 len: 46
1284 { skbaddr: ffff8800d46bd500 } hitcount: 1 len: 116
1285 { skbaddr: ffff88005f3d5f00 } hitcount: 1 len: 1280
1286 { skbaddr: ffff880100064700 } hitcount: 1 len: 365
1287 { skbaddr: ffff8800badb6f00 } hitcount: 1 len: 60
1288 .
1289 .
1290 .
1291 { skbaddr: ffff88009fe0be00 } hitcount: 27 len: 24677
1292 { skbaddr: ffff88009fe0a400 } hitcount: 27 len: 23052
1293 { skbaddr: ffff88009fe0b700 } hitcount: 31 len: 25589
1294 { skbaddr: ffff88009fe0b600 } hitcount: 32 len: 27326
1295 { skbaddr: ffff88006a462800 } hitcount: 68 len: 71678
1296 { skbaddr: ffff88006a463700 } hitcount: 70 len: 72678
1297 { skbaddr: ffff88006a462b00 } hitcount: 71 len: 77589
1298 { skbaddr: ffff88006a463600 } hitcount: 73 len: 71307
1299 { skbaddr: ffff88006a462200 } hitcount: 81 len: 81032
1300
1301 Totals:
1302 Hits: 1451
1303 Entries: 318
1304 Dropped: 0
1305
1306
1307 # event histogram
1308 #
1309 # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len == 256 [active]
1310 #
1311
1312
1313 Totals:
1314 Hits: 0
1315 Entries: 0
1316 Dropped: 0
1317
1318
1319 # event histogram
1320 #
1321 # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len > 4096 [active]
1322 #
1323
1324 { skbaddr: ffff88009fd2c300 } hitcount: 1 len: 7212
1325 { skbaddr: ffff8800d2bcce00 } hitcount: 1 len: 7212
1326 { skbaddr: ffff8800d2bcd700 } hitcount: 1 len: 7212
1327 { skbaddr: ffff8800d2bcda00 } hitcount: 1 len: 21492
1328 { skbaddr: ffff8800ae2e2d00 } hitcount: 1 len: 7212
1329 { skbaddr: ffff8800d2bcdb00 } hitcount: 1 len: 7212
1330 { skbaddr: ffff88006a4df500 } hitcount: 1 len: 4854
1331 { skbaddr: ffff88008ce47b00 } hitcount: 1 len: 18636
1332 { skbaddr: ffff8800ae2e2200 } hitcount: 1 len: 12924
1333 { skbaddr: ffff88005f3e1000 } hitcount: 1 len: 4356
1334 { skbaddr: ffff8800d2bcdc00 } hitcount: 2 len: 24420
1335 { skbaddr: ffff8800d2bcc200 } hitcount: 2 len: 12996
1336
1337 Totals:
1338 Hits: 14
1339 Entries: 12
1340 Dropped: 0
1341
1342
1343 # event histogram
1344 #
1345 # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len < 0 [active]
1346 #
1347
1348
1349 Totals:
1350 Hits: 0
1351 Entries: 0
1352 Dropped: 0
1353
1354 Named triggers can be used to have triggers share a common set of
1355 histogram data. This capability is mostly useful for combining the
1356 output of events generated by tracepoints contained inside inline
1357 functions, but names can be used in a hist trigger on any event.
1358 For example, these two triggers when hit will update the same 'len'
1359 field in the shared 'foo' histogram data::
1360
1361 # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
1362 /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
1363 # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
1364 /sys/kernel/debug/tracing/events/net/netif_rx/trigger
1365
1366 You can see that they're updating common histogram data by reading
1367 each event's hist files at the same time::
1368
1369 # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist;
1370 cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
1371
1372 # event histogram
1373 #
1374 # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
1375 #
1376
1377 { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46
1378 { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76
1379 { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46
1380 { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468
1381 { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46
1382 { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52
1383 { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168
1384 { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46
1385 { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260
1386 { skbaddr: ffff880064505000 } hitcount: 1 len: 46
1387 { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32
1388 { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46
1389 { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44
1390 { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168
1391 { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40
1392 { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40
1393 { skbaddr: ffff880064505f00 } hitcount: 1 len: 174
1394 { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160
1395 { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76
1396 { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46
1397 { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32
1398 { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46
1399 { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988
1400 { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46
1401 { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44
1402 { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676
1403 { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107
1404 { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92
1405 { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142
1406 { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220
1407 { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92
1408 { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92
1409 { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675
1410 { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138
1411 { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138
1412 { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184
1413 { skbaddr: ffff880064504400 } hitcount: 4 len: 184
1414 { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184
1415 { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230
1416 { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196
1417 { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276
1418 { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276
1419
1420 Totals:
1421 Hits: 81
1422 Entries: 42
1423 Dropped: 0
1424 # event histogram
1425 #
1426 # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
1427 #
1428
1429 { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46
1430 { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76
1431 { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46
1432 { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468
1433 { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46
1434 { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52
1435 { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168
1436 { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46
1437 { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260
1438 { skbaddr: ffff880064505000 } hitcount: 1 len: 46
1439 { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32
1440 { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46
1441 { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44
1442 { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168
1443 { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40
1444 { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40
1445 { skbaddr: ffff880064505f00 } hitcount: 1 len: 174
1446 { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160
1447 { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76
1448 { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46
1449 { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32
1450 { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46
1451 { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988
1452 { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46
1453 { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44
1454 { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676
1455 { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107
1456 { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92
1457 { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142
1458 { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220
1459 { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92
1460 { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92
1461 { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675
1462 { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138
1463 { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138
1464 { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184
1465 { skbaddr: ffff880064504400 } hitcount: 4 len: 184
1466 { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184
1467 { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230
1468 { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196
1469 { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276
1470 { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276
1471
1472 Totals:
1473 Hits: 81
1474 Entries: 42
1475 Dropped: 0
1476
1477 And here's an example that shows how to combine histogram data from
1478 any two events even if they don't share any 'compatible' fields
1479 other than 'hitcount' and 'stacktrace'. These commands create a
1480 couple of triggers named 'bar' using those fields::
1481
1482 # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
1483 /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
1484 # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
1485 /sys/kernel/debug/tracing/events/net/netif_rx/trigger
1486
1487 And displaying the output of either shows some interesting if
1488 somewhat confusing output::
1489
1490 # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
1491 # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
1492
1493 # event histogram
1494 #
1495 # trigger info: hist:name=bar:keys=stacktrace:vals=hitcount:sort=hitcount:size=2048 [active]
1496 #
1497
1498 { stacktrace:
1499 kernel_clone+0x18e/0x330
1500 kernel_thread+0x29/0x30
1501 kthreadd+0x154/0x1b0
1502 ret_from_fork+0x3f/0x70
1503 } hitcount: 1
1504 { stacktrace:
1505 netif_rx_internal+0xb2/0xd0
1506 netif_rx_ni+0x20/0x70
1507 dev_loopback_xmit+0xaa/0xd0
1508 ip_mc_output+0x126/0x240
1509 ip_local_out_sk+0x31/0x40
1510 igmp_send_report+0x1e9/0x230
1511 igmp_timer_expire+0xe9/0x120
1512 call_timer_fn+0x39/0xf0
1513 run_timer_softirq+0x1e1/0x290
1514 __do_softirq+0xfd/0x290
1515 irq_exit+0x98/0xb0
1516 smp_apic_timer_interrupt+0x4a/0x60
1517 apic_timer_interrupt+0x6d/0x80
1518 cpuidle_enter+0x17/0x20
1519 call_cpuidle+0x3b/0x60
1520 cpu_startup_entry+0x22d/0x310
1521 } hitcount: 1
1522 { stacktrace:
1523 netif_rx_internal+0xb2/0xd0
1524 netif_rx_ni+0x20/0x70
1525 dev_loopback_xmit+0xaa/0xd0
1526 ip_mc_output+0x17f/0x240
1527 ip_local_out_sk+0x31/0x40
1528 ip_send_skb+0x1a/0x50
1529 udp_send_skb+0x13e/0x270
1530 udp_sendmsg+0x2bf/0x980
1531 inet_sendmsg+0x67/0xa0
1532 sock_sendmsg+0x38/0x50
1533 SYSC_sendto+0xef/0x170
1534 SyS_sendto+0xe/0x10
1535 entry_SYSCALL_64_fastpath+0x12/0x6a
1536 } hitcount: 2
1537 { stacktrace:
1538 netif_rx_internal+0xb2/0xd0
1539 netif_rx+0x1c/0x60
1540 loopback_xmit+0x6c/0xb0
1541 dev_hard_start_xmit+0x219/0x3a0
1542 __dev_queue_xmit+0x415/0x4f0
1543 dev_queue_xmit_sk+0x13/0x20
1544 ip_finish_output2+0x237/0x340
1545 ip_finish_output+0x113/0x1d0
1546 ip_output+0x66/0xc0
1547 ip_local_out_sk+0x31/0x40
1548 ip_send_skb+0x1a/0x50
1549 udp_send_skb+0x16d/0x270
1550 udp_sendmsg+0x2bf/0x980
1551 inet_sendmsg+0x67/0xa0
1552 sock_sendmsg+0x38/0x50
1553 ___sys_sendmsg+0x14e/0x270
1554 } hitcount: 76
1555 { stacktrace:
1556 netif_rx_internal+0xb2/0xd0
1557 netif_rx+0x1c/0x60
1558 loopback_xmit+0x6c/0xb0
1559 dev_hard_start_xmit+0x219/0x3a0
1560 __dev_queue_xmit+0x415/0x4f0
1561 dev_queue_xmit_sk+0x13/0x20
1562 ip_finish_output2+0x237/0x340
1563 ip_finish_output+0x113/0x1d0
1564 ip_output+0x66/0xc0
1565 ip_local_out_sk+0x31/0x40
1566 ip_send_skb+0x1a/0x50
1567 udp_send_skb+0x16d/0x270
1568 udp_sendmsg+0x2bf/0x980
1569 inet_sendmsg+0x67/0xa0
1570 sock_sendmsg+0x38/0x50
1571 ___sys_sendmsg+0x269/0x270
1572 } hitcount: 77
1573 { stacktrace:
1574 netif_rx_internal+0xb2/0xd0
1575 netif_rx+0x1c/0x60
1576 loopback_xmit+0x6c/0xb0
1577 dev_hard_start_xmit+0x219/0x3a0
1578 __dev_queue_xmit+0x415/0x4f0
1579 dev_queue_xmit_sk+0x13/0x20
1580 ip_finish_output2+0x237/0x340
1581 ip_finish_output+0x113/0x1d0
1582 ip_output+0x66/0xc0
1583 ip_local_out_sk+0x31/0x40
1584 ip_send_skb+0x1a/0x50
1585 udp_send_skb+0x16d/0x270
1586 udp_sendmsg+0x2bf/0x980
1587 inet_sendmsg+0x67/0xa0
1588 sock_sendmsg+0x38/0x50
1589 SYSC_sendto+0xef/0x170
1590 } hitcount: 88
1591 { stacktrace:
1592 kernel_clone+0x18e/0x330
1593 SyS_clone+0x19/0x20
1594 entry_SYSCALL_64_fastpath+0x12/0x6a
1595 } hitcount: 244
1596
1597 Totals:
1598 Hits: 489
1599 Entries: 7
1600 Dropped: 0
1601
1602 2.2 Inter-event hist triggers
1603 -----------------------------
1604
1605 Inter-event hist triggers are hist triggers that combine values from
1606 one or more other events and create a histogram using that data. Data
1607 from an inter-event histogram can in turn become the source for
1608 further combined histograms, thus providing a chain of related
1609 histograms, which is important for some applications.
1610
1611 The most important example of an inter-event quantity that can be used
1612 in this manner is latency, which is simply a difference in timestamps
1613 between two events. Although latency is the most important
1614 inter-event quantity, note that because the support is completely
1615 general across the trace event subsystem, any event field can be used
1616 in an inter-event quantity.
1617
1618 An example of a histogram that combines data from other histograms
1619 into a useful chain would be a 'wakeupswitch latency' histogram that
1620 combines a 'wakeup latency' histogram and a 'switch latency'
1621 histogram.
1622
1623 Normally, a hist trigger specification consists of a (possibly
1624 compound) key along with one or more numeric values, which are
1625 continually updated sums associated with that key. A histogram
1626 specification in this case consists of individual key and value
1627 specifications that refer to trace event fields associated with a
1628 single event type.
1629
1630 The inter-event hist trigger extension allows fields from multiple
1631 events to be referenced and combined into a multi-event histogram
1632 specification. In support of this overall goal, a few enabling
1633 features have been added to the hist trigger support:
1634
1635 - In order to compute an inter-event quantity, a value from one
1636 event needs to saved and then referenced from another event. This
1637 requires the introduction of support for histogram 'variables'.
1638
1639 - The computation of inter-event quantities and their combination
1640 require some minimal amount of support for applying simple
1641 expressions to variables (+ and -).
1642
1643 - A histogram consisting of inter-event quantities isn't logically a
1644 histogram on either event (so having the 'hist' file for either
1645 event host the histogram output doesn't really make sense). To
1646 address the idea that the histogram is associated with a
1647 combination of events, support is added allowing the creation of
1648 'synthetic' events that are events derived from other events.
1649 These synthetic events are full-fledged events just like any other
1650 and can be used as such, as for instance to create the
1651 'combination' histograms mentioned previously.
1652
1653 - A set of 'actions' can be associated with histogram entries -
1654 these can be used to generate the previously mentioned synthetic
1655 events, but can also be used for other purposes, such as for
1656 example saving context when a 'max' latency has been hit.
1657
1658 - Trace events don't have a 'timestamp' associated with them, but
1659 there is an implicit timestamp saved along with an event in the
1660 underlying ftrace ring buffer. This timestamp is now exposed as a
1661 a synthetic field named 'common_timestamp' which can be used in
1662 histograms as if it were any other event field; it isn't an actual
1663 field in the trace format but rather is a synthesized value that
1664 nonetheless can be used as if it were an actual field. By default
1665 it is in units of nanoseconds; appending '.usecs' to a
1666 common_timestamp field changes the units to microseconds.
1667
1668 A note on inter-event timestamps: If common_timestamp is used in a
1669 histogram, the trace buffer is automatically switched over to using
1670 absolute timestamps and the "global" trace clock, in order to avoid
1671 bogus timestamp differences with other clocks that aren't coherent
1672 across CPUs. This can be overridden by specifying one of the other
1673 trace clocks instead, using the "clock=XXX" hist trigger attribute,
1674 where XXX is any of the clocks listed in the tracing/trace_clock
1675 pseudo-file.
1676
1677 These features are described in more detail in the following sections.
1678
1679 2.2.1 Histogram Variables
1680 -------------------------
1681
1682 Variables are simply named locations used for saving and retrieving
1683 values between matching events. A 'matching' event is defined as an
1684 event that has a matching key - if a variable is saved for a histogram
1685 entry corresponding to that key, any subsequent event with a matching
1686 key can access that variable.
1687
1688 A variable's value is normally available to any subsequent event until
1689 it is set to something else by a subsequent event. The one exception
1690 to that rule is that any variable used in an expression is essentially
1691 'read-once' - once it's used by an expression in a subsequent event,
1692 it's reset to its 'unset' state, which means it can't be used again
1693 unless it's set again. This ensures not only that an event doesn't
1694 use an uninitialized variable in a calculation, but that that variable
1695 is used only once and not for any unrelated subsequent match.
1696
1697 The basic syntax for saving a variable is to simply prefix a unique
1698 variable name not corresponding to any keyword along with an '=' sign
1699 to any event field.
1700
1701 Either keys or values can be saved and retrieved in this way. This
1702 creates a variable named 'ts0' for a histogram entry with the key
1703 'next_pid'::
1704
1705 # echo 'hist:keys=next_pid:vals=$ts0:ts0=common_timestamp ... >> \
1706 event/trigger
1707
1708 The ts0 variable can be accessed by any subsequent event having the
1709 same pid as 'next_pid'.
1710
1711 Variable references are formed by prepending the variable name with
1712 the '$' sign. Thus for example, the ts0 variable above would be
1713 referenced as '$ts0' in expressions.
1714
1715 Because 'vals=' is used, the common_timestamp variable value above
1716 will also be summed as a normal histogram value would (though for a
1717 timestamp it makes little sense).
1718
1719 The below shows that a key value can also be saved in the same way::
1720
1721 # echo 'hist:timer_pid=common_pid:key=timer_pid ...' >> event/trigger
1722
1723 If a variable isn't a key variable or prefixed with 'vals=', the
1724 associated event field will be saved in a variable but won't be summed
1725 as a value::
1726
1727 # echo 'hist:keys=next_pid:ts1=common_timestamp ...' >> event/trigger
1728
1729 Multiple variables can be assigned at the same time. The below would
1730 result in both ts0 and b being created as variables, with both
1731 common_timestamp and field1 additionally being summed as values::
1732
1733 # echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ...' >> \
1734 event/trigger
1735
1736 Note that variable assignments can appear either preceding or
1737 following their use. The command below behaves identically to the
1738 command above::
1739
1740 # echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ...' >> \
1741 event/trigger
1742
1743 Any number of variables not bound to a 'vals=' prefix can also be
1744 assigned by simply separating them with colons. Below is the same
1745 thing but without the values being summed in the histogram::
1746
1747 # echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ...' >> event/trigger
1748
1749 Variables set as above can be referenced and used in expressions on
1750 another event.
1751
1752 For example, here's how a latency can be calculated::
1753
1754 # echo 'hist:keys=pid,prio:ts0=common_timestamp ...' >> event1/trigger
1755 # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ...' >> event2/trigger
1756
1757 In the first line above, the event's timestamp is saved into the
1758 variable ts0. In the next line, ts0 is subtracted from the second
1759 event's timestamp to produce the latency, which is then assigned into
1760 yet another variable, 'wakeup_lat'. The hist trigger below in turn
1761 makes use of the wakeup_lat variable to compute a combined latency
1762 using the same key and variable from yet another event::
1763
1764 # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ...' >> event3/trigger
1765
1766 Expressions support the use of addition, subtraction, multiplication and
1767 division operators (+-\*/).
1768
1769 Note if division by zero cannot be detected at parse time (i.e. the
1770 divisor is not a constant), the result will be -1.
1771
1772 Numeric constants can also be used directly in an expression::
1773
1774 # echo 'hist:keys=next_pid:timestamp_secs=common_timestamp/1000000 ...' >> event/trigger
1775
1776 or assigned to a variable and referenced in a subsequent expression::
1777
1778 # echo 'hist:keys=next_pid:us_per_sec=1000000 ...' >> event/trigger
1779 # echo 'hist:keys=next_pid:timestamp_secs=common_timestamp/$us_per_sec ...' >> event/trigger
1780
1781 2.2.2 Synthetic Events
1782 ----------------------
1783
1784 Synthetic events are user-defined events generated from hist trigger
1785 variables or fields associated with one or more other events. Their
1786 purpose is to provide a mechanism for displaying data spanning
1787 multiple events consistent with the existing and already familiar
1788 usage for normal events.
1789
1790 To define a synthetic event, the user writes a simple specification
1791 consisting of the name of the new event along with one or more
1792 variables and their types, which can be any valid field type,
1793 separated by semicolons, to the tracing/synthetic_events file.
1794
1795 See synth_field_size() for available types.
1796
1797 If field_name contains [n], the field is considered to be a static array.
1798
1799 If field_names contains[] (no subscript), the field is considered to
1800 be a dynamic array, which will only take as much space in the event as
1801 is required to hold the array.
1802
1803 A string field can be specified using either the static notation:
1804
1805 char name[32];
1806
1807 Or the dynamic:
1808
1809 char name[];
1810
1811 The size limit for either is 256.
1812
1813 For instance, the following creates a new event named 'wakeup_latency'
1814 with 3 fields: lat, pid, and prio. Each of those fields is simply a
1815 variable reference to a variable on another event::
1816
1817 # echo 'wakeup_latency \
1818 u64 lat; \
1819 pid_t pid; \
1820 int prio' >> \
1821 /sys/kernel/debug/tracing/synthetic_events
1822
1823 Reading the tracing/synthetic_events file lists all the currently
1824 defined synthetic events, in this case the event defined above::
1825
1826 # cat /sys/kernel/debug/tracing/synthetic_events
1827 wakeup_latency u64 lat; pid_t pid; int prio
1828
1829 An existing synthetic event definition can be removed by prepending
1830 the command that defined it with a '!'::
1831
1832 # echo '!wakeup_latency u64 lat pid_t pid int prio' >> \
1833 /sys/kernel/debug/tracing/synthetic_events
1834
1835 At this point, there isn't yet an actual 'wakeup_latency' event
1836 instantiated in the event subsystem - for this to happen, a 'hist
1837 trigger action' needs to be instantiated and bound to actual fields
1838 and variables defined on other events (see Section 2.2.3 below on
1839 how that is done using hist trigger 'onmatch' action). Once that is
1840 done, the 'wakeup_latency' synthetic event instance is created.
1841
1842 The new event is created under the tracing/events/synthetic/ directory
1843 and looks and behaves just like any other event::
1844
1845 # ls /sys/kernel/debug/tracing/events/synthetic/wakeup_latency
1846 enable filter format hist id trigger
1847
1848 A histogram can now be defined for the new synthetic event::
1849
1850 # echo 'hist:keys=pid,prio,lat.log2:sort=lat' >> \
1851 /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
1852
1853 The above shows the latency "lat" in a power of 2 grouping.
1854
1855 Like any other event, once a histogram is enabled for the event, the
1856 output can be displayed by reading the event's 'hist' file.
1857
1858 # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist
1859
1860 # event histogram
1861 #
1862 # trigger info: hist:keys=pid,prio,lat.log2:vals=hitcount:sort=lat.log2:size=2048 [active]
1863 #
1864
1865 { pid: 2035, prio: 9, lat: ~ 2^2 } hitcount: 43
1866 { pid: 2034, prio: 9, lat: ~ 2^2 } hitcount: 60
1867 { pid: 2029, prio: 9, lat: ~ 2^2 } hitcount: 965
1868 { pid: 2034, prio: 120, lat: ~ 2^2 } hitcount: 9
1869 { pid: 2033, prio: 120, lat: ~ 2^2 } hitcount: 5
1870 { pid: 2030, prio: 9, lat: ~ 2^2 } hitcount: 335
1871 { pid: 2030, prio: 120, lat: ~ 2^2 } hitcount: 10
1872 { pid: 2032, prio: 120, lat: ~ 2^2 } hitcount: 1
1873 { pid: 2035, prio: 120, lat: ~ 2^2 } hitcount: 2
1874 { pid: 2031, prio: 9, lat: ~ 2^2 } hitcount: 176
1875 { pid: 2028, prio: 120, lat: ~ 2^2 } hitcount: 15
1876 { pid: 2033, prio: 9, lat: ~ 2^2 } hitcount: 91
1877 { pid: 2032, prio: 9, lat: ~ 2^2 } hitcount: 125
1878 { pid: 2029, prio: 120, lat: ~ 2^2 } hitcount: 4
1879 { pid: 2031, prio: 120, lat: ~ 2^2 } hitcount: 3
1880 { pid: 2029, prio: 120, lat: ~ 2^3 } hitcount: 2
1881 { pid: 2035, prio: 9, lat: ~ 2^3 } hitcount: 41
1882 { pid: 2030, prio: 120, lat: ~ 2^3 } hitcount: 1
1883 { pid: 2032, prio: 9, lat: ~ 2^3 } hitcount: 32
1884 { pid: 2031, prio: 9, lat: ~ 2^3 } hitcount: 44
1885 { pid: 2034, prio: 9, lat: ~ 2^3 } hitcount: 40
1886 { pid: 2030, prio: 9, lat: ~ 2^3 } hitcount: 29
1887 { pid: 2033, prio: 9, lat: ~ 2^3 } hitcount: 31
1888 { pid: 2029, prio: 9, lat: ~ 2^3 } hitcount: 31
1889 { pid: 2028, prio: 120, lat: ~ 2^3 } hitcount: 18
1890 { pid: 2031, prio: 120, lat: ~ 2^3 } hitcount: 2
1891 { pid: 2028, prio: 120, lat: ~ 2^4 } hitcount: 1
1892 { pid: 2029, prio: 9, lat: ~ 2^4 } hitcount: 4
1893 { pid: 2031, prio: 120, lat: ~ 2^7 } hitcount: 1
1894 { pid: 2032, prio: 120, lat: ~ 2^7 } hitcount: 1
1895
1896 Totals:
1897 Hits: 2122
1898 Entries: 30
1899 Dropped: 0
1900
1901
1902 The latency values can also be grouped linearly by a given size with
1903 the ".buckets" modifier and specify a size (in this case groups of 10).
1904
1905 # echo 'hist:keys=pid,prio,lat.buckets=10:sort=lat' >> \
1906 /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
1907
1908 # event histogram
1909 #
1910 # trigger info: hist:keys=pid,prio,lat.buckets=10:vals=hitcount:sort=lat.buckets=10:size=2048 [active]
1911 #
1912
1913 { pid: 2067, prio: 9, lat: ~ 0-9 } hitcount: 220
1914 { pid: 2068, prio: 9, lat: ~ 0-9 } hitcount: 157
1915 { pid: 2070, prio: 9, lat: ~ 0-9 } hitcount: 100
1916 { pid: 2067, prio: 120, lat: ~ 0-9 } hitcount: 6
1917 { pid: 2065, prio: 120, lat: ~ 0-9 } hitcount: 2
1918 { pid: 2066, prio: 120, lat: ~ 0-9 } hitcount: 2
1919 { pid: 2069, prio: 9, lat: ~ 0-9 } hitcount: 122
1920 { pid: 2069, prio: 120, lat: ~ 0-9 } hitcount: 8
1921 { pid: 2070, prio: 120, lat: ~ 0-9 } hitcount: 1
1922 { pid: 2068, prio: 120, lat: ~ 0-9 } hitcount: 7
1923 { pid: 2066, prio: 9, lat: ~ 0-9 } hitcount: 365
1924 { pid: 2064, prio: 120, lat: ~ 0-9 } hitcount: 35
1925 { pid: 2065, prio: 9, lat: ~ 0-9 } hitcount: 998
1926 { pid: 2071, prio: 9, lat: ~ 0-9 } hitcount: 85
1927 { pid: 2065, prio: 9, lat: ~ 10-19 } hitcount: 2
1928 { pid: 2064, prio: 120, lat: ~ 10-19 } hitcount: 2
1929
1930 Totals:
1931 Hits: 2112
1932 Entries: 16
1933 Dropped: 0
1934
1935 2.2.3 Hist trigger 'handlers' and 'actions'
1936 -------------------------------------------
1937
1938 A hist trigger 'action' is a function that's executed (in most cases
1939 conditionally) whenever a histogram entry is added or updated.
1940
1941 When a histogram entry is added or updated, a hist trigger 'handler'
1942 is what decides whether the corresponding action is actually invoked
1943 or not.
1944
1945 Hist trigger handlers and actions are paired together in the general
1946 form:
1947
1948 <handler>.<action>
1949
1950 To specify a handler.action pair for a given event, simply specify
1951 that handler.action pair between colons in the hist trigger
1952 specification.
1953
1954 In theory, any handler can be combined with any action, but in
1955 practice, not every handler.action combination is currently supported;
1956 if a given handler.action combination isn't supported, the hist
1957 trigger will fail with -EINVAL;
1958
1959 The default 'handler.action' if none is explicitly specified is as it
1960 always has been, to simply update the set of values associated with an
1961 entry. Some applications, however, may want to perform additional
1962 actions at that point, such as generate another event, or compare and
1963 save a maximum.
1964
1965 The supported handlers and actions are listed below, and each is
1966 described in more detail in the following paragraphs, in the context
1967 of descriptions of some common and useful handler.action combinations.
1968
1969 The available handlers are:
1970
1971 - onmatch(matching.event) - invoke action on any addition or update
1972 - onmax(var) - invoke action if var exceeds current max
1973 - onchange(var) - invoke action if var changes
1974
1975 The available actions are:
1976
1977 - trace(<synthetic_event_name>,param list) - generate synthetic event
1978 - save(field,...) - save current event fields
1979 - snapshot() - snapshot the trace buffer
1980
1981 The following commonly-used handler.action pairs are available:
1982
1983 - onmatch(matching.event).trace(<synthetic_event_name>,param list)
1984
1985 The 'onmatch(matching.event).trace(<synthetic_event_name>,param
1986 list)' hist trigger action is invoked whenever an event matches
1987 and the histogram entry would be added or updated. It causes the
1988 named synthetic event to be generated with the values given in the
1989 'param list'. The result is the generation of a synthetic event
1990 that consists of the values contained in those variables at the
1991 time the invoking event was hit. For example, if the synthetic
1992 event name is 'wakeup_latency', a wakeup_latency event is
1993 generated using onmatch(event).trace(wakeup_latency,arg1,arg2).
1994
1995 There is also an equivalent alternative form available for
1996 generating synthetic events. In this form, the synthetic event
1997 name is used as if it were a function name. For example, using
1998 the 'wakeup_latency' synthetic event name again, the
1999 wakeup_latency event would be generated by invoking it as if it
2000 were a function call, with the event field values passed in as
2001 arguments: onmatch(event).wakeup_latency(arg1,arg2). The syntax
2002 for this form is:
2003
2004 onmatch(matching.event).<synthetic_event_name>(param list)
2005
2006 In either case, the 'param list' consists of one or more
2007 parameters which may be either variables or fields defined on
2008 either the 'matching.event' or the target event. The variables or
2009 fields specified in the param list may be either fully-qualified
2010 or unqualified. If a variable is specified as unqualified, it
2011 must be unique between the two events. A field name used as a
2012 param can be unqualified if it refers to the target event, but
2013 must be fully qualified if it refers to the matching event. A
2014 fully-qualified name is of the form 'system.event_name.$var_name'
2015 or 'system.event_name.field'.
2016
2017 The 'matching.event' specification is simply the fully qualified
2018 event name of the event that matches the target event for the
2019 onmatch() functionality, in the form 'system.event_name'. Histogram
2020 keys of both events are compared to find if events match. In case
2021 multiple histogram keys are used, they all must match in the specified
2022 order.
2023
2024 Finally, the number and type of variables/fields in the 'param
2025 list' must match the number and types of the fields in the
2026 synthetic event being generated.
2027
2028 As an example the below defines a simple synthetic event and uses
2029 a variable defined on the sched_wakeup_new event as a parameter
2030 when invoking the synthetic event. Here we define the synthetic
2031 event::
2032
2033 # echo 'wakeup_new_test pid_t pid' >> \
2034 /sys/kernel/debug/tracing/synthetic_events
2035
2036 # cat /sys/kernel/debug/tracing/synthetic_events
2037 wakeup_new_test pid_t pid
2038
2039 The following hist trigger both defines the missing testpid
2040 variable and specifies an onmatch() action that generates a
2041 wakeup_new_test synthetic event whenever a sched_wakeup_new event
2042 occurs, which because of the 'if comm == "cyclictest"' filter only
2043 happens when the executable is cyclictest::
2044
2045 # echo 'hist:keys=$testpid:testpid=pid:onmatch(sched.sched_wakeup_new).\
2046 wakeup_new_test($testpid) if comm=="cyclictest"' >> \
2047 /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger
2048
2049 Or, equivalently, using the 'trace' keyword syntax:
2050
2051 # echo 'hist:keys=$testpid:testpid=pid:onmatch(sched.sched_wakeup_new).\
2052 trace(wakeup_new_test,$testpid) if comm=="cyclictest"' >> \
2053 /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger
2054
2055 Creating and displaying a histogram based on those events is now
2056 just a matter of using the fields and new synthetic event in the
2057 tracing/events/synthetic directory, as usual::
2058
2059 # echo 'hist:keys=pid:sort=pid' >> \
2060 /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/trigger
2061
2062 Running 'cyclictest' should cause wakeup_new events to generate
2063 wakeup_new_test synthetic events which should result in histogram
2064 output in the wakeup_new_test event's hist file::
2065
2066 # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/hist
2067
2068 A more typical usage would be to use two events to calculate a
2069 latency. The following example uses a set of hist triggers to
2070 produce a 'wakeup_latency' histogram.
2071
2072 First, we define a 'wakeup_latency' synthetic event::
2073
2074 # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \
2075 /sys/kernel/debug/tracing/synthetic_events
2076
2077 Next, we specify that whenever we see a sched_waking event for a
2078 cyclictest thread, save the timestamp in a 'ts0' variable::
2079
2080 # echo 'hist:keys=$saved_pid:saved_pid=pid:ts0=common_timestamp.usecs \
2081 if comm=="cyclictest"' >> \
2082 /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
2083
2084 Then, when the corresponding thread is actually scheduled onto the
2085 CPU by a sched_switch event (saved_pid matches next_pid), calculate
2086 the latency and use that along with another variable and an event field
2087 to generate a wakeup_latency synthetic event::
2088
2089 # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0:\
2090 onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,\
2091 $saved_pid,next_prio) if next_comm=="cyclictest"' >> \
2092 /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
2093
2094 We also need to create a histogram on the wakeup_latency synthetic
2095 event in order to aggregate the generated synthetic event data::
2096
2097 # echo 'hist:keys=pid,prio,lat:sort=pid,lat' >> \
2098 /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
2099
2100 Finally, once we've run cyclictest to actually generate some
2101 events, we can see the output by looking at the wakeup_latency
2102 synthetic event's hist file::
2103
2104 # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist
2105
2106 - onmax(var).save(field,.. .)
2107
2108 The 'onmax(var).save(field,...)' hist trigger action is invoked
2109 whenever the value of 'var' associated with a histogram entry
2110 exceeds the current maximum contained in that variable.
2111
2112 The end result is that the trace event fields specified as the
2113 onmax.save() params will be saved if 'var' exceeds the current
2114 maximum for that hist trigger entry. This allows context from the
2115 event that exhibited the new maximum to be saved for later
2116 reference. When the histogram is displayed, additional fields
2117 displaying the saved values will be printed.
2118
2119 As an example the below defines a couple of hist triggers, one for
2120 sched_waking and another for sched_switch, keyed on pid. Whenever
2121 a sched_waking occurs, the timestamp is saved in the entry
2122 corresponding to the current pid, and when the scheduler switches
2123 back to that pid, the timestamp difference is calculated. If the
2124 resulting latency, stored in wakeup_lat, exceeds the current
2125 maximum latency, the values specified in the save() fields are
2126 recorded::
2127
2128 # echo 'hist:keys=pid:ts0=common_timestamp.usecs \
2129 if comm=="cyclictest"' >> \
2130 /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
2131
2132 # echo 'hist:keys=next_pid:\
2133 wakeup_lat=common_timestamp.usecs-$ts0:\
2134 onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) \
2135 if next_comm=="cyclictest"' >> \
2136 /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
2137
2138 When the histogram is displayed, the max value and the saved
2139 values corresponding to the max are displayed following the rest
2140 of the fields::
2141
2142 # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist
2143 { next_pid: 2255 } hitcount: 239
2144 common_timestamp-ts0: 0
2145 max: 27
2146 next_comm: cyclictest
2147 prev_pid: 0 prev_prio: 120 prev_comm: swapper/1
2148
2149 { next_pid: 2256 } hitcount: 2355
2150 common_timestamp-ts0: 0
2151 max: 49 next_comm: cyclictest
2152 prev_pid: 0 prev_prio: 120 prev_comm: swapper/0
2153
2154 Totals:
2155 Hits: 12970
2156 Entries: 2
2157 Dropped: 0
2158
2159 - onmax(var).snapshot()
2160
2161 The 'onmax(var).snapshot()' hist trigger action is invoked
2162 whenever the value of 'var' associated with a histogram entry
2163 exceeds the current maximum contained in that variable.
2164
2165 The end result is that a global snapshot of the trace buffer will
2166 be saved in the tracing/snapshot file if 'var' exceeds the current
2167 maximum for any hist trigger entry.
2168
2169 Note that in this case the maximum is a global maximum for the
2170 current trace instance, which is the maximum across all buckets of
2171 the histogram. The key of the specific trace event that caused
2172 the global maximum and the global maximum itself are displayed,
2173 along with a message stating that a snapshot has been taken and
2174 where to find it. The user can use the key information displayed
2175 to locate the corresponding bucket in the histogram for even more
2176 detail.
2177
2178 As an example the below defines a couple of hist triggers, one for
2179 sched_waking and another for sched_switch, keyed on pid. Whenever
2180 a sched_waking event occurs, the timestamp is saved in the entry
2181 corresponding to the current pid, and when the scheduler switches
2182 back to that pid, the timestamp difference is calculated. If the
2183 resulting latency, stored in wakeup_lat, exceeds the current
2184 maximum latency, a snapshot is taken. As part of the setup, all
2185 the scheduler events are also enabled, which are the events that
2186 will show up in the snapshot when it is taken at some point:
2187
2188 # echo 1 > /sys/kernel/debug/tracing/events/sched/enable
2189
2190 # echo 'hist:keys=pid:ts0=common_timestamp.usecs \
2191 if comm=="cyclictest"' >> \
2192 /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
2193
2194 # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0: \
2195 onmax($wakeup_lat).save(next_prio,next_comm,prev_pid,prev_prio, \
2196 prev_comm):onmax($wakeup_lat).snapshot() \
2197 if next_comm=="cyclictest"' >> \
2198 /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
2199
2200 When the histogram is displayed, for each bucket the max value
2201 and the saved values corresponding to the max are displayed
2202 following the rest of the fields.
2203
2204 If a snapshot was taken, there is also a message indicating that,
2205 along with the value and event that triggered the global maximum:
2206
2207 # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist
2208 { next_pid: 2101 } hitcount: 200
2209 max: 52 next_prio: 120 next_comm: cyclictest \
2210 prev_pid: 0 prev_prio: 120 prev_comm: swapper/6
2211
2212 { next_pid: 2103 } hitcount: 1326
2213 max: 572 next_prio: 19 next_comm: cyclictest \
2214 prev_pid: 0 prev_prio: 120 prev_comm: swapper/1
2215
2216 { next_pid: 2102 } hitcount: 1982 \
2217 max: 74 next_prio: 19 next_comm: cyclictest \
2218 prev_pid: 0 prev_prio: 120 prev_comm: swapper/5
2219
2220 Snapshot taken (see tracing/snapshot). Details:
2221 triggering value { onmax($wakeup_lat) }: 572 \
2222 triggered by event with key: { next_pid: 2103 }
2223
2224 Totals:
2225 Hits: 3508
2226 Entries: 3
2227 Dropped: 0
2228
2229 In the above case, the event that triggered the global maximum has
2230 the key with next_pid == 2103. If you look at the bucket that has
2231 2103 as the key, you'll find the additional values save()'d along
2232 with the local maximum for that bucket, which should be the same
2233 as the global maximum (since that was the same value that
2234 triggered the global snapshot).
2235
2236 And finally, looking at the snapshot data should show at or near
2237 the end the event that triggered the snapshot (in this case you
2238 can verify the timestamps between the sched_waking and
2239 sched_switch events, which should match the time displayed in the
2240 global maximum)::
2241
2242 # cat /sys/kernel/debug/tracing/snapshot
2243
2244 <...>-2103 [005] d..3 309.873125: sched_switch: prev_comm=cyclictest prev_pid=2103 prev_prio=19 prev_state=D ==> next_comm=swapper/5 next_pid=0 next_prio=120
2245 <idle>-0 [005] d.h3 309.873611: sched_waking: comm=cyclictest pid=2102 prio=19 target_cpu=005
2246 <idle>-0 [005] dNh4 309.873613: sched_wakeup: comm=cyclictest pid=2102 prio=19 target_cpu=005
2247 <idle>-0 [005] d..3 309.873616: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=S ==> next_comm=cyclictest next_pid=2102 next_prio=19
2248 <...>-2102 [005] d..3 309.873625: sched_switch: prev_comm=cyclictest prev_pid=2102 prev_prio=19 prev_state=D ==> next_comm=swapper/5 next_pid=0 next_prio=120
2249 <idle>-0 [005] d.h3 309.874624: sched_waking: comm=cyclictest pid=2102 prio=19 target_cpu=005
2250 <idle>-0 [005] dNh4 309.874626: sched_wakeup: comm=cyclictest pid=2102 prio=19 target_cpu=005
2251 <idle>-0 [005] dNh3 309.874628: sched_waking: comm=cyclictest pid=2103 prio=19 target_cpu=005
2252 <idle>-0 [005] dNh4 309.874630: sched_wakeup: comm=cyclictest pid=2103 prio=19 target_cpu=005
2253 <idle>-0 [005] d..3 309.874633: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=S ==> next_comm=cyclictest next_pid=2102 next_prio=19
2254 <idle>-0 [004] d.h3 309.874757: sched_waking: comm=gnome-terminal- pid=1699 prio=120 target_cpu=004
2255 <idle>-0 [004] dNh4 309.874762: sched_wakeup: comm=gnome-terminal- pid=1699 prio=120 target_cpu=004
2256 <idle>-0 [004] d..3 309.874766: sched_switch: prev_comm=swapper/4 prev_pid=0 prev_prio=120 prev_state=S ==> next_comm=gnome-terminal- next_pid=1699 next_prio=120
2257 gnome-terminal--1699 [004] d.h2 309.874941: sched_stat_runtime: comm=gnome-terminal- pid=1699 runtime=180706 [ns] vruntime=1126870572 [ns]
2258 <idle>-0 [003] d.s4 309.874956: sched_waking: comm=rcu_sched pid=9 prio=120 target_cpu=007
2259 <idle>-0 [003] d.s5 309.874960: sched_wake_idle_without_ipi: cpu=7
2260 <idle>-0 [003] d.s5 309.874961: sched_wakeup: comm=rcu_sched pid=9 prio=120 target_cpu=007
2261 <idle>-0 [007] d..3 309.874963: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=S ==> next_comm=rcu_sched next_pid=9 next_prio=120
2262 rcu_sched-9 [007] d..3 309.874973: sched_stat_runtime: comm=rcu_sched pid=9 runtime=13646 [ns] vruntime=22531430286 [ns]
2263 rcu_sched-9 [007] d..3 309.874978: sched_switch: prev_comm=rcu_sched prev_pid=9 prev_prio=120 prev_state=R+ ==> next_comm=swapper/7 next_pid=0 next_prio=120
2264 <...>-2102 [005] d..4 309.874994: sched_migrate_task: comm=cyclictest pid=2103 prio=19 orig_cpu=5 dest_cpu=1
2265 <...>-2102 [005] d..4 309.875185: sched_wake_idle_without_ipi: cpu=1
2266 <idle>-0 [001] d..3 309.875200: sched_switch: prev_comm=swapper/1 prev_pid=0 prev_prio=120 prev_state=S ==> next_comm=cyclictest next_pid=2103 next_prio=19
2267
2268 - onchange(var).save(field,.. .)
2269
2270 The 'onchange(var).save(field,...)' hist trigger action is invoked
2271 whenever the value of 'var' associated with a histogram entry
2272 changes.
2273
2274 The end result is that the trace event fields specified as the
2275 onchange.save() params will be saved if 'var' changes for that
2276 hist trigger entry. This allows context from the event that
2277 changed the value to be saved for later reference. When the
2278 histogram is displayed, additional fields displaying the saved
2279 values will be printed.
2280
2281 - onchange(var).snapshot()
2282
2283 The 'onchange(var).snapshot()' hist trigger action is invoked
2284 whenever the value of 'var' associated with a histogram entry
2285 changes.
2286
2287 The end result is that a global snapshot of the trace buffer will
2288 be saved in the tracing/snapshot file if 'var' changes for any
2289 hist trigger entry.
2290
2291 Note that in this case the changed value is a global variable
2292 associated with current trace instance. The key of the specific
2293 trace event that caused the value to change and the global value
2294 itself are displayed, along with a message stating that a snapshot
2295 has been taken and where to find it. The user can use the key
2296 information displayed to locate the corresponding bucket in the
2297 histogram for even more detail.
2298
2299 As an example the below defines a hist trigger on the tcp_probe
2300 event, keyed on dport. Whenever a tcp_probe event occurs, the
2301 cwnd field is checked against the current value stored in the
2302 $cwnd variable. If the value has changed, a snapshot is taken.
2303 As part of the setup, all the scheduler and tcp events are also
2304 enabled, which are the events that will show up in the snapshot
2305 when it is taken at some point:
2306
2307 # echo 1 > /sys/kernel/debug/tracing/events/sched/enable
2308 # echo 1 > /sys/kernel/debug/tracing/events/tcp/enable
2309
2310 # echo 'hist:keys=dport:cwnd=snd_cwnd: \
2311 onchange($cwnd).save(snd_wnd,srtt,rcv_wnd): \
2312 onchange($cwnd).snapshot()' >> \
2313 /sys/kernel/debug/tracing/events/tcp/tcp_probe/trigger
2314
2315 When the histogram is displayed, for each bucket the tracked value
2316 and the saved values corresponding to that value are displayed
2317 following the rest of the fields.
2318
2319 If a snapshot was taken, there is also a message indicating that,
2320 along with the value and event that triggered the snapshot::
2321
2322 # cat /sys/kernel/debug/tracing/events/tcp/tcp_probe/hist
2323
2324 { dport: 1521 } hitcount: 8
2325 changed: 10 snd_wnd: 35456 srtt: 154262 rcv_wnd: 42112
2326
2327 { dport: 80 } hitcount: 23
2328 changed: 10 snd_wnd: 28960 srtt: 19604 rcv_wnd: 29312
2329
2330 { dport: 9001 } hitcount: 172
2331 changed: 10 snd_wnd: 48384 srtt: 260444 rcv_wnd: 55168
2332
2333 { dport: 443 } hitcount: 211
2334 changed: 10 snd_wnd: 26960 srtt: 17379 rcv_wnd: 28800
2335
2336 Snapshot taken (see tracing/snapshot). Details::
2337
2338 triggering value { onchange($cwnd) }: 10
2339 triggered by event with key: { dport: 80 }
2340
2341 Totals:
2342 Hits: 414
2343 Entries: 4
2344 Dropped: 0
2345
2346 In the above case, the event that triggered the snapshot has the
2347 key with dport == 80. If you look at the bucket that has 80 as
2348 the key, you'll find the additional values save()'d along with the
2349 changed value for that bucket, which should be the same as the
2350 global changed value (since that was the same value that triggered
2351 the global snapshot).
2352
2353 And finally, looking at the snapshot data should show at or near
2354 the end the event that triggered the snapshot::
2355
2356 # cat /sys/kernel/debug/tracing/snapshot
2357
2358 gnome-shell-1261 [006] dN.3 49.823113: sched_stat_runtime: comm=gnome-shell pid=1261 runtime=49347 [ns] vruntime=1835730389 [ns]
2359 kworker/u16:4-773 [003] d..3 49.823114: sched_switch: prev_comm=kworker/u16:4 prev_pid=773 prev_prio=120 prev_state=R+ ==> next_comm=kworker/3:2 next_pid=135 next_prio=120
2360 gnome-shell-1261 [006] d..3 49.823114: sched_switch: prev_comm=gnome-shell prev_pid=1261 prev_prio=120 prev_state=R+ ==> next_comm=kworker/6:2 next_pid=387 next_prio=120
2361 kworker/3:2-135 [003] d..3 49.823118: sched_stat_runtime: comm=kworker/3:2 pid=135 runtime=5339 [ns] vruntime=17815800388 [ns]
2362 kworker/6:2-387 [006] d..3 49.823120: sched_stat_runtime: comm=kworker/6:2 pid=387 runtime=9594 [ns] vruntime=14589605367 [ns]
2363 kworker/6:2-387 [006] d..3 49.823122: sched_switch: prev_comm=kworker/6:2 prev_pid=387 prev_prio=120 prev_state=R+ ==> next_comm=gnome-shell next_pid=1261 next_prio=120
2364 kworker/3:2-135 [003] d..3 49.823123: sched_switch: prev_comm=kworker/3:2 prev_pid=135 prev_prio=120 prev_state=T ==> next_comm=swapper/3 next_pid=0 next_prio=120
2365 <idle>-0 [004] ..s7 49.823798: tcp_probe: src=10.0.0.10:54326 dest=23.215.104.193:80 mark=0x0 length=32 snd_nxt=0xe3ae2ff5 snd_una=0xe3ae2ecd snd_cwnd=10 ssthresh=2147483647 snd_wnd=28960 srtt=19604 rcv_wnd=29312
2366
2367 3. User space creating a trigger
2368 --------------------------------
2369
2370 Writing into /sys/kernel/tracing/trace_marker writes into the ftrace
2371 ring buffer. This can also act like an event, by writing into the trigger
2372 file located in /sys/kernel/tracing/events/ftrace/print/
2373
2374 Modifying cyclictest to write into the trace_marker file before it sleeps
2375 and after it wakes up, something like this::
2376
2377 static void traceputs(char *str)
2378 {
2379 /* tracemark_fd is the trace_marker file descriptor */
2380 if (tracemark_fd < 0)
2381 return;
2382 /* write the tracemark message */
2383 write(tracemark_fd, str, strlen(str));
2384 }
2385
2386 And later add something like::
2387
2388 traceputs("start");
2389 clock_nanosleep(...);
2390 traceputs("end");
2391
2392 We can make a histogram from this::
2393
2394 # cd /sys/kernel/tracing
2395 # echo 'latency u64 lat' > synthetic_events
2396 # echo 'hist:keys=common_pid:ts0=common_timestamp.usecs if buf == "start"' > events/ftrace/print/trigger
2397 # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(ftrace.print).latency($lat) if buf == "end"' >> events/ftrace/print/trigger
2398 # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger
2399
2400 The above created a synthetic event called "latency" and two histograms
2401 against the trace_marker, one gets triggered when "start" is written into the
2402 trace_marker file and the other when "end" is written. If the pids match, then
2403 it will call the "latency" synthetic event with the calculated latency as its
2404 parameter. Finally, a histogram is added to the latency synthetic event to
2405 record the calculated latency along with the pid.
2406
2407 Now running cyclictest with::
2408
2409 # ./cyclictest -p80 -d0 -i250 -n -a -t --tracemark -b 1000
2410
2411 -p80 : run threads at priority 80
2412 -d0 : have all threads run at the same interval
2413 -i250 : start the interval at 250 microseconds (all threads will do this)
2414 -n : sleep with nanosleep
2415 -a : affine all threads to a separate CPU
2416 -t : one thread per available CPU
2417 --tracemark : enable trace mark writing
2418 -b 1000 : stop if any latency is greater than 1000 microseconds
2419
2420 Note, the -b 1000 is used just to make --tracemark available.
2421
2422 Then we can see the histogram created by this with::
2423
2424 # cat events/synthetic/latency/hist
2425 # event histogram
2426 #
2427 # trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active]
2428 #
2429
2430 { lat: 107, common_pid: 2039 } hitcount: 1
2431 { lat: 122, common_pid: 2041 } hitcount: 1
2432 { lat: 166, common_pid: 2039 } hitcount: 1
2433 { lat: 174, common_pid: 2039 } hitcount: 1
2434 { lat: 194, common_pid: 2041 } hitcount: 1
2435 { lat: 196, common_pid: 2036 } hitcount: 1
2436 { lat: 197, common_pid: 2038 } hitcount: 1
2437 { lat: 198, common_pid: 2039 } hitcount: 1
2438 { lat: 199, common_pid: 2039 } hitcount: 1
2439 { lat: 200, common_pid: 2041 } hitcount: 1
2440 { lat: 201, common_pid: 2039 } hitcount: 2
2441 { lat: 202, common_pid: 2038 } hitcount: 1
2442 { lat: 202, common_pid: 2043 } hitcount: 1
2443 { lat: 203, common_pid: 2039 } hitcount: 1
2444 { lat: 203, common_pid: 2036 } hitcount: 1
2445 { lat: 203, common_pid: 2041 } hitcount: 1
2446 { lat: 206, common_pid: 2038 } hitcount: 2
2447 { lat: 207, common_pid: 2039 } hitcount: 1
2448 { lat: 207, common_pid: 2036 } hitcount: 1
2449 { lat: 208, common_pid: 2040 } hitcount: 1
2450 { lat: 209, common_pid: 2043 } hitcount: 1
2451 { lat: 210, common_pid: 2039 } hitcount: 1
2452 { lat: 211, common_pid: 2039 } hitcount: 4
2453 { lat: 212, common_pid: 2043 } hitcount: 1
2454 { lat: 212, common_pid: 2039 } hitcount: 2
2455 { lat: 213, common_pid: 2039 } hitcount: 1
2456 { lat: 214, common_pid: 2038 } hitcount: 1
2457 { lat: 214, common_pid: 2039 } hitcount: 2
2458 { lat: 214, common_pid: 2042 } hitcount: 1
2459 { lat: 215, common_pid: 2039 } hitcount: 1
2460 { lat: 217, common_pid: 2036 } hitcount: 1
2461 { lat: 217, common_pid: 2040 } hitcount: 1
2462 { lat: 217, common_pid: 2039 } hitcount: 1
2463 { lat: 218, common_pid: 2039 } hitcount: 6
2464 { lat: 219, common_pid: 2039 } hitcount: 9
2465 { lat: 220, common_pid: 2039 } hitcount: 11
2466 { lat: 221, common_pid: 2039 } hitcount: 5
2467 { lat: 221, common_pid: 2042 } hitcount: 1
2468 { lat: 222, common_pid: 2039 } hitcount: 7
2469 { lat: 223, common_pid: 2036 } hitcount: 1
2470 { lat: 223, common_pid: 2039 } hitcount: 3
2471 { lat: 224, common_pid: 2039 } hitcount: 4
2472 { lat: 224, common_pid: 2037 } hitcount: 1
2473 { lat: 224, common_pid: 2036 } hitcount: 2
2474 { lat: 225, common_pid: 2039 } hitcount: 5
2475 { lat: 225, common_pid: 2042 } hitcount: 1
2476 { lat: 226, common_pid: 2039 } hitcount: 7
2477 { lat: 226, common_pid: 2036 } hitcount: 4
2478 { lat: 227, common_pid: 2039 } hitcount: 6
2479 { lat: 227, common_pid: 2036 } hitcount: 12
2480 { lat: 227, common_pid: 2043 } hitcount: 1
2481 { lat: 228, common_pid: 2039 } hitcount: 7
2482 { lat: 228, common_pid: 2036 } hitcount: 14
2483 { lat: 229, common_pid: 2039 } hitcount: 9
2484 { lat: 229, common_pid: 2036 } hitcount: 8
2485 { lat: 229, common_pid: 2038 } hitcount: 1
2486 { lat: 230, common_pid: 2039 } hitcount: 11
2487 { lat: 230, common_pid: 2036 } hitcount: 6
2488 { lat: 230, common_pid: 2043 } hitcount: 1
2489 { lat: 230, common_pid: 2042 } hitcount: 2
2490 { lat: 231, common_pid: 2041 } hitcount: 1
2491 { lat: 231, common_pid: 2036 } hitcount: 6
2492 { lat: 231, common_pid: 2043 } hitcount: 1
2493 { lat: 231, common_pid: 2039 } hitcount: 8
2494 { lat: 232, common_pid: 2037 } hitcount: 1
2495 { lat: 232, common_pid: 2039 } hitcount: 6
2496 { lat: 232, common_pid: 2040 } hitcount: 2
2497 { lat: 232, common_pid: 2036 } hitcount: 5
2498 { lat: 232, common_pid: 2043 } hitcount: 1
2499 { lat: 233, common_pid: 2036 } hitcount: 5
2500 { lat: 233, common_pid: 2039 } hitcount: 11
2501 { lat: 234, common_pid: 2039 } hitcount: 4
2502 { lat: 234, common_pid: 2038 } hitcount: 2
2503 { lat: 234, common_pid: 2043 } hitcount: 2
2504 { lat: 234, common_pid: 2036 } hitcount: 11
2505 { lat: 234, common_pid: 2040 } hitcount: 1
2506 { lat: 235, common_pid: 2037 } hitcount: 2
2507 { lat: 235, common_pid: 2036 } hitcount: 8
2508 { lat: 235, common_pid: 2043 } hitcount: 2
2509 { lat: 235, common_pid: 2039 } hitcount: 5
2510 { lat: 235, common_pid: 2042 } hitcount: 2
2511 { lat: 235, common_pid: 2040 } hitcount: 4
2512 { lat: 235, common_pid: 2041 } hitcount: 1
2513 { lat: 236, common_pid: 2036 } hitcount: 7
2514 { lat: 236, common_pid: 2037 } hitcount: 1
2515 { lat: 236, common_pid: 2041 } hitcount: 5
2516 { lat: 236, common_pid: 2039 } hitcount: 3
2517 { lat: 236, common_pid: 2043 } hitcount: 9
2518 { lat: 236, common_pid: 2040 } hitcount: 7
2519 { lat: 237, common_pid: 2037 } hitcount: 1
2520 { lat: 237, common_pid: 2040 } hitcount: 1
2521 { lat: 237, common_pid: 2036 } hitcount: 9
2522 { lat: 237, common_pid: 2039 } hitcount: 3
2523 { lat: 237, common_pid: 2043 } hitcount: 8
2524 { lat: 237, common_pid: 2042 } hitcount: 2
2525 { lat: 237, common_pid: 2041 } hitcount: 2
2526 { lat: 238, common_pid: 2043 } hitcount: 10
2527 { lat: 238, common_pid: 2040 } hitcount: 1
2528 { lat: 238, common_pid: 2037 } hitcount: 9
2529 { lat: 238, common_pid: 2038 } hitcount: 1
2530 { lat: 238, common_pid: 2039 } hitcount: 1
2531 { lat: 238, common_pid: 2042 } hitcount: 3
2532 { lat: 238, common_pid: 2036 } hitcount: 7
2533 { lat: 239, common_pid: 2041 } hitcount: 1
2534 { lat: 239, common_pid: 2043 } hitcount: 11
2535 { lat: 239, common_pid: 2037 } hitcount: 11
2536 { lat: 239, common_pid: 2038 } hitcount: 6
2537 { lat: 239, common_pid: 2036 } hitcount: 7
2538 { lat: 239, common_pid: 2040 } hitcount: 1
2539 { lat: 239, common_pid: 2042 } hitcount: 9
2540 { lat: 240, common_pid: 2037 } hitcount: 29
2541 { lat: 240, common_pid: 2043 } hitcount: 15
2542 { lat: 240, common_pid: 2040 } hitcount: 44
2543 { lat: 240, common_pid: 2039 } hitcount: 1
2544 { lat: 240, common_pid: 2041 } hitcount: 2
2545 { lat: 240, common_pid: 2038 } hitcount: 1
2546 { lat: 240, common_pid: 2036 } hitcount: 10
2547 { lat: 240, common_pid: 2042 } hitcount: 13
2548 { lat: 241, common_pid: 2036 } hitcount: 21
2549 { lat: 241, common_pid: 2041 } hitcount: 36
2550 { lat: 241, common_pid: 2037 } hitcount: 34
2551 { lat: 241, common_pid: 2042 } hitcount: 14
2552 { lat: 241, common_pid: 2040 } hitcount: 94
2553 { lat: 241, common_pid: 2039 } hitcount: 12
2554 { lat: 241, common_pid: 2038 } hitcount: 2
2555 { lat: 241, common_pid: 2043 } hitcount: 28
2556 { lat: 242, common_pid: 2040 } hitcount: 109
2557 { lat: 242, common_pid: 2041 } hitcount: 506
2558 { lat: 242, common_pid: 2039 } hitcount: 155
2559 { lat: 242, common_pid: 2042 } hitcount: 21
2560 { lat: 242, common_pid: 2037 } hitcount: 52
2561 { lat: 242, common_pid: 2043 } hitcount: 21
2562 { lat: 242, common_pid: 2036 } hitcount: 16
2563 { lat: 242, common_pid: 2038 } hitcount: 156
2564 { lat: 243, common_pid: 2037 } hitcount: 46
2565 { lat: 243, common_pid: 2039 } hitcount: 40
2566 { lat: 243, common_pid: 2042 } hitcount: 119
2567 { lat: 243, common_pid: 2041 } hitcount: 611
2568 { lat: 243, common_pid: 2036 } hitcount: 69
2569 { lat: 243, common_pid: 2038 } hitcount: 784
2570 { lat: 243, common_pid: 2040 } hitcount: 323
2571 { lat: 243, common_pid: 2043 } hitcount: 14
2572 { lat: 244, common_pid: 2043 } hitcount: 35
2573 { lat: 244, common_pid: 2042 } hitcount: 305
2574 { lat: 244, common_pid: 2039 } hitcount: 8
2575 { lat: 244, common_pid: 2040 } hitcount: 4515
2576 { lat: 244, common_pid: 2038 } hitcount: 371
2577 { lat: 244, common_pid: 2037 } hitcount: 31
2578 { lat: 244, common_pid: 2036 } hitcount: 114
2579 { lat: 244, common_pid: 2041 } hitcount: 3396
2580 { lat: 245, common_pid: 2036 } hitcount: 700
2581 { lat: 245, common_pid: 2041 } hitcount: 2772
2582 { lat: 245, common_pid: 2037 } hitcount: 268
2583 { lat: 245, common_pid: 2039 } hitcount: 472
2584 { lat: 245, common_pid: 2038 } hitcount: 2758
2585 { lat: 245, common_pid: 2042 } hitcount: 3833
2586 { lat: 245, common_pid: 2040 } hitcount: 3105
2587 { lat: 245, common_pid: 2043 } hitcount: 645
2588 { lat: 246, common_pid: 2038 } hitcount: 3451
2589 { lat: 246, common_pid: 2041 } hitcount: 142
2590 { lat: 246, common_pid: 2037 } hitcount: 5101
2591 { lat: 246, common_pid: 2040 } hitcount: 68
2592 { lat: 246, common_pid: 2043 } hitcount: 5099
2593 { lat: 246, common_pid: 2039 } hitcount: 5608
2594 { lat: 246, common_pid: 2042 } hitcount: 3723
2595 { lat: 246, common_pid: 2036 } hitcount: 4738
2596 { lat: 247, common_pid: 2042 } hitcount: 312
2597 { lat: 247, common_pid: 2043 } hitcount: 2385
2598 { lat: 247, common_pid: 2041 } hitcount: 452
2599 { lat: 247, common_pid: 2038 } hitcount: 792
2600 { lat: 247, common_pid: 2040 } hitcount: 78
2601 { lat: 247, common_pid: 2036 } hitcount: 2375
2602 { lat: 247, common_pid: 2039 } hitcount: 1834
2603 { lat: 247, common_pid: 2037 } hitcount: 2655
2604 { lat: 248, common_pid: 2037 } hitcount: 36
2605 { lat: 248, common_pid: 2042 } hitcount: 11
2606 { lat: 248, common_pid: 2038 } hitcount: 122
2607 { lat: 248, common_pid: 2036 } hitcount: 135
2608 { lat: 248, common_pid: 2039 } hitcount: 26
2609 { lat: 248, common_pid: 2041 } hitcount: 503
2610 { lat: 248, common_pid: 2043 } hitcount: 66
2611 { lat: 248, common_pid: 2040 } hitcount: 46
2612 { lat: 249, common_pid: 2037 } hitcount: 29
2613 { lat: 249, common_pid: 2038 } hitcount: 1
2614 { lat: 249, common_pid: 2043 } hitcount: 29
2615 { lat: 249, common_pid: 2039 } hitcount: 8
2616 { lat: 249, common_pid: 2042 } hitcount: 56
2617 { lat: 249, common_pid: 2040 } hitcount: 27
2618 { lat: 249, common_pid: 2041 } hitcount: 11
2619 { lat: 249, common_pid: 2036 } hitcount: 27
2620 { lat: 250, common_pid: 2038 } hitcount: 1
2621 { lat: 250, common_pid: 2036 } hitcount: 30
2622 { lat: 250, common_pid: 2040 } hitcount: 19
2623 { lat: 250, common_pid: 2043 } hitcount: 22
2624 { lat: 250, common_pid: 2042 } hitcount: 20
2625 { lat: 250, common_pid: 2041 } hitcount: 1
2626 { lat: 250, common_pid: 2039 } hitcount: 6
2627 { lat: 250, common_pid: 2037 } hitcount: 48
2628 { lat: 251, common_pid: 2037 } hitcount: 43
2629 { lat: 251, common_pid: 2039 } hitcount: 1
2630 { lat: 251, common_pid: 2036 } hitcount: 12
2631 { lat: 251, common_pid: 2042 } hitcount: 2
2632 { lat: 251, common_pid: 2041 } hitcount: 1
2633 { lat: 251, common_pid: 2043 } hitcount: 15
2634 { lat: 251, common_pid: 2040 } hitcount: 3
2635 { lat: 252, common_pid: 2040 } hitcount: 1
2636 { lat: 252, common_pid: 2036 } hitcount: 12
2637 { lat: 252, common_pid: 2037 } hitcount: 21
2638 { lat: 252, common_pid: 2043 } hitcount: 14
2639 { lat: 253, common_pid: 2037 } hitcount: 21
2640 { lat: 253, common_pid: 2039 } hitcount: 2
2641 { lat: 253, common_pid: 2036 } hitcount: 9
2642 { lat: 253, common_pid: 2043 } hitcount: 6
2643 { lat: 253, common_pid: 2040 } hitcount: 1
2644 { lat: 254, common_pid: 2036 } hitcount: 8
2645 { lat: 254, common_pid: 2043 } hitcount: 3
2646 { lat: 254, common_pid: 2041 } hitcount: 1
2647 { lat: 254, common_pid: 2042 } hitcount: 1
2648 { lat: 254, common_pid: 2039 } hitcount: 1
2649 { lat: 254, common_pid: 2037 } hitcount: 12
2650 { lat: 255, common_pid: 2043 } hitcount: 1
2651 { lat: 255, common_pid: 2037 } hitcount: 2
2652 { lat: 255, common_pid: 2036 } hitcount: 2
2653 { lat: 255, common_pid: 2039 } hitcount: 8
2654 { lat: 256, common_pid: 2043 } hitcount: 1
2655 { lat: 256, common_pid: 2036 } hitcount: 4
2656 { lat: 256, common_pid: 2039 } hitcount: 6
2657 { lat: 257, common_pid: 2039 } hitcount: 5
2658 { lat: 257, common_pid: 2036 } hitcount: 4
2659 { lat: 258, common_pid: 2039 } hitcount: 5
2660 { lat: 258, common_pid: 2036 } hitcount: 2
2661 { lat: 259, common_pid: 2036 } hitcount: 7
2662 { lat: 259, common_pid: 2039 } hitcount: 7
2663 { lat: 260, common_pid: 2036 } hitcount: 8
2664 { lat: 260, common_pid: 2039 } hitcount: 6
2665 { lat: 261, common_pid: 2036 } hitcount: 5
2666 { lat: 261, common_pid: 2039 } hitcount: 7
2667 { lat: 262, common_pid: 2039 } hitcount: 5
2668 { lat: 262, common_pid: 2036 } hitcount: 5
2669 { lat: 263, common_pid: 2039 } hitcount: 7
2670 { lat: 263, common_pid: 2036 } hitcount: 7
2671 { lat: 264, common_pid: 2039 } hitcount: 9
2672 { lat: 264, common_pid: 2036 } hitcount: 9
2673 { lat: 265, common_pid: 2036 } hitcount: 5
2674 { lat: 265, common_pid: 2039 } hitcount: 1
2675 { lat: 266, common_pid: 2036 } hitcount: 1
2676 { lat: 266, common_pid: 2039 } hitcount: 3
2677 { lat: 267, common_pid: 2036 } hitcount: 1
2678 { lat: 267, common_pid: 2039 } hitcount: 3
2679 { lat: 268, common_pid: 2036 } hitcount: 1
2680 { lat: 268, common_pid: 2039 } hitcount: 6
2681 { lat: 269, common_pid: 2036 } hitcount: 1
2682 { lat: 269, common_pid: 2043 } hitcount: 1
2683 { lat: 269, common_pid: 2039 } hitcount: 2
2684 { lat: 270, common_pid: 2040 } hitcount: 1
2685 { lat: 270, common_pid: 2039 } hitcount: 6
2686 { lat: 271, common_pid: 2041 } hitcount: 1
2687 { lat: 271, common_pid: 2039 } hitcount: 5
2688 { lat: 272, common_pid: 2039 } hitcount: 10
2689 { lat: 273, common_pid: 2039 } hitcount: 8
2690 { lat: 274, common_pid: 2039 } hitcount: 2
2691 { lat: 275, common_pid: 2039 } hitcount: 1
2692 { lat: 276, common_pid: 2039 } hitcount: 2
2693 { lat: 276, common_pid: 2037 } hitcount: 1
2694 { lat: 276, common_pid: 2038 } hitcount: 1
2695 { lat: 277, common_pid: 2039 } hitcount: 1
2696 { lat: 277, common_pid: 2042 } hitcount: 1
2697 { lat: 278, common_pid: 2039 } hitcount: 1
2698 { lat: 279, common_pid: 2039 } hitcount: 4
2699 { lat: 279, common_pid: 2043 } hitcount: 1
2700 { lat: 280, common_pid: 2039 } hitcount: 3
2701 { lat: 283, common_pid: 2036 } hitcount: 2
2702 { lat: 284, common_pid: 2039 } hitcount: 1
2703 { lat: 284, common_pid: 2043 } hitcount: 1
2704 { lat: 288, common_pid: 2039 } hitcount: 1
2705 { lat: 289, common_pid: 2039 } hitcount: 1
2706 { lat: 300, common_pid: 2039 } hitcount: 1
2707 { lat: 384, common_pid: 2039 } hitcount: 1
2708
2709 Totals:
2710 Hits: 67625
2711 Entries: 278
2712 Dropped: 0
2713
2714 Note, the writes are around the sleep, so ideally they will all be of 250
2715 microseconds. If you are wondering how there are several that are under
2716 250 microseconds, that is because the way cyclictest works, is if one
2717 iteration comes in late, the next one will set the timer to wake up less that
2718 250. That is, if an iteration came in 50 microseconds late, the next wake up
2719 will be at 200 microseconds.
2720
2721 But this could easily be done in userspace. To make this even more
2722 interesting, we can mix the histogram between events that happened in the
2723 kernel with trace_marker::
2724
2725 # cd /sys/kernel/tracing
2726 # echo 'latency u64 lat' > synthetic_events
2727 # echo 'hist:keys=pid:ts0=common_timestamp.usecs' > events/sched/sched_waking/trigger
2728 # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(sched.sched_waking).latency($lat) if buf == "end"' > events/ftrace/print/trigger
2729 # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger
2730
2731 The difference this time is that instead of using the trace_marker to start
2732 the latency, the sched_waking event is used, matching the common_pid for the
2733 trace_marker write with the pid that is being woken by sched_waking.
2734
2735 After running cyclictest again with the same parameters, we now have::
2736
2737 # cat events/synthetic/latency/hist
2738 # event histogram
2739 #
2740 # trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active]
2741 #
2742
2743 { lat: 7, common_pid: 2302 } hitcount: 640
2744 { lat: 7, common_pid: 2299 } hitcount: 42
2745 { lat: 7, common_pid: 2303 } hitcount: 18
2746 { lat: 7, common_pid: 2305 } hitcount: 166
2747 { lat: 7, common_pid: 2306 } hitcount: 1
2748 { lat: 7, common_pid: 2301 } hitcount: 91
2749 { lat: 7, common_pid: 2300 } hitcount: 17
2750 { lat: 8, common_pid: 2303 } hitcount: 8296
2751 { lat: 8, common_pid: 2304 } hitcount: 6864
2752 { lat: 8, common_pid: 2305 } hitcount: 9464
2753 { lat: 8, common_pid: 2301 } hitcount: 9213
2754 { lat: 8, common_pid: 2306 } hitcount: 6246
2755 { lat: 8, common_pid: 2302 } hitcount: 8797
2756 { lat: 8, common_pid: 2299 } hitcount: 8771
2757 { lat: 8, common_pid: 2300 } hitcount: 8119
2758 { lat: 9, common_pid: 2305 } hitcount: 1519
2759 { lat: 9, common_pid: 2299 } hitcount: 2346
2760 { lat: 9, common_pid: 2303 } hitcount: 2841
2761 { lat: 9, common_pid: 2301 } hitcount: 1846
2762 { lat: 9, common_pid: 2304 } hitcount: 3861
2763 { lat: 9, common_pid: 2302 } hitcount: 1210
2764 { lat: 9, common_pid: 2300 } hitcount: 2762
2765 { lat: 9, common_pid: 2306 } hitcount: 4247
2766 { lat: 10, common_pid: 2299 } hitcount: 16
2767 { lat: 10, common_pid: 2306 } hitcount: 333
2768 { lat: 10, common_pid: 2303 } hitcount: 16
2769 { lat: 10, common_pid: 2304 } hitcount: 168
2770 { lat: 10, common_pid: 2302 } hitcount: 240
2771 { lat: 10, common_pid: 2301 } hitcount: 28
2772 { lat: 10, common_pid: 2300 } hitcount: 95
2773 { lat: 10, common_pid: 2305 } hitcount: 18
2774 { lat: 11, common_pid: 2303 } hitcount: 5
2775 { lat: 11, common_pid: 2305 } hitcount: 8
2776 { lat: 11, common_pid: 2306 } hitcount: 221
2777 { lat: 11, common_pid: 2302 } hitcount: 76
2778 { lat: 11, common_pid: 2304 } hitcount: 26
2779 { lat: 11, common_pid: 2300 } hitcount: 125
2780 { lat: 11, common_pid: 2299 } hitcount: 2
2781 { lat: 12, common_pid: 2305 } hitcount: 3
2782 { lat: 12, common_pid: 2300 } hitcount: 6
2783 { lat: 12, common_pid: 2306 } hitcount: 90
2784 { lat: 12, common_pid: 2302 } hitcount: 4
2785 { lat: 12, common_pid: 2303 } hitcount: 1
2786 { lat: 12, common_pid: 2304 } hitcount: 122
2787 { lat: 13, common_pid: 2300 } hitcount: 12
2788 { lat: 13, common_pid: 2301 } hitcount: 1
2789 { lat: 13, common_pid: 2306 } hitcount: 32
2790 { lat: 13, common_pid: 2302 } hitcount: 5
2791 { lat: 13, common_pid: 2305 } hitcount: 1
2792 { lat: 13, common_pid: 2303 } hitcount: 1
2793 { lat: 13, common_pid: 2304 } hitcount: 61
2794 { lat: 14, common_pid: 2303 } hitcount: 4
2795 { lat: 14, common_pid: 2306 } hitcount: 5
2796 { lat: 14, common_pid: 2305 } hitcount: 4
2797 { lat: 14, common_pid: 2304 } hitcount: 62
2798 { lat: 14, common_pid: 2302 } hitcount: 19
2799 { lat: 14, common_pid: 2300 } hitcount: 33
2800 { lat: 14, common_pid: 2299 } hitcount: 1
2801 { lat: 14, common_pid: 2301 } hitcount: 4
2802 { lat: 15, common_pid: 2305 } hitcount: 1
2803 { lat: 15, common_pid: 2302 } hitcount: 25
2804 { lat: 15, common_pid: 2300 } hitcount: 11
2805 { lat: 15, common_pid: 2299 } hitcount: 5
2806 { lat: 15, common_pid: 2301 } hitcount: 1
2807 { lat: 15, common_pid: 2304 } hitcount: 8
2808 { lat: 15, common_pid: 2303 } hitcount: 1
2809 { lat: 15, common_pid: 2306 } hitcount: 6
2810 { lat: 16, common_pid: 2302 } hitcount: 31
2811 { lat: 16, common_pid: 2306 } hitcount: 3
2812 { lat: 16, common_pid: 2300 } hitcount: 5
2813 { lat: 17, common_pid: 2302 } hitcount: 6
2814 { lat: 17, common_pid: 2303 } hitcount: 1
2815 { lat: 18, common_pid: 2304 } hitcount: 1
2816 { lat: 18, common_pid: 2302 } hitcount: 8
2817 { lat: 18, common_pid: 2299 } hitcount: 1
2818 { lat: 18, common_pid: 2301 } hitcount: 1
2819 { lat: 19, common_pid: 2303 } hitcount: 4
2820 { lat: 19, common_pid: 2304 } hitcount: 5
2821 { lat: 19, common_pid: 2302 } hitcount: 4
2822 { lat: 19, common_pid: 2299 } hitcount: 3
2823 { lat: 19, common_pid: 2306 } hitcount: 1
2824 { lat: 19, common_pid: 2300 } hitcount: 4
2825 { lat: 19, common_pid: 2305 } hitcount: 5
2826 { lat: 20, common_pid: 2299 } hitcount: 2
2827 { lat: 20, common_pid: 2302 } hitcount: 3
2828 { lat: 20, common_pid: 2305 } hitcount: 1
2829 { lat: 20, common_pid: 2300 } hitcount: 2
2830 { lat: 20, common_pid: 2301 } hitcount: 2
2831 { lat: 20, common_pid: 2303 } hitcount: 3
2832 { lat: 21, common_pid: 2305 } hitcount: 1
2833 { lat: 21, common_pid: 2299 } hitcount: 5
2834 { lat: 21, common_pid: 2303 } hitcount: 4
2835 { lat: 21, common_pid: 2302 } hitcount: 7
2836 { lat: 21, common_pid: 2300 } hitcount: 1
2837 { lat: 21, common_pid: 2301 } hitcount: 5
2838 { lat: 21, common_pid: 2304 } hitcount: 2
2839 { lat: 22, common_pid: 2302 } hitcount: 5
2840 { lat: 22, common_pid: 2303 } hitcount: 1
2841 { lat: 22, common_pid: 2306 } hitcount: 3
2842 { lat: 22, common_pid: 2301 } hitcount: 2
2843 { lat: 22, common_pid: 2300 } hitcount: 1
2844 { lat: 22, common_pid: 2299 } hitcount: 1
2845 { lat: 22, common_pid: 2305 } hitcount: 1
2846 { lat: 22, common_pid: 2304 } hitcount: 1
2847 { lat: 23, common_pid: 2299 } hitcount: 1
2848 { lat: 23, common_pid: 2306 } hitcount: 2
2849 { lat: 23, common_pid: 2302 } hitcount: 6
2850 { lat: 24, common_pid: 2302 } hitcount: 3
2851 { lat: 24, common_pid: 2300 } hitcount: 1
2852 { lat: 24, common_pid: 2306 } hitcount: 2
2853 { lat: 24, common_pid: 2305 } hitcount: 1
2854 { lat: 24, common_pid: 2299 } hitcount: 1
2855 { lat: 25, common_pid: 2300 } hitcount: 1
2856 { lat: 25, common_pid: 2302 } hitcount: 4
2857 { lat: 26, common_pid: 2302 } hitcount: 2
2858 { lat: 27, common_pid: 2305 } hitcount: 1
2859 { lat: 27, common_pid: 2300 } hitcount: 1
2860 { lat: 27, common_pid: 2302 } hitcount: 3
2861 { lat: 28, common_pid: 2306 } hitcount: 1
2862 { lat: 28, common_pid: 2302 } hitcount: 4
2863 { lat: 29, common_pid: 2302 } hitcount: 1
2864 { lat: 29, common_pid: 2300 } hitcount: 2
2865 { lat: 29, common_pid: 2306 } hitcount: 1
2866 { lat: 29, common_pid: 2304 } hitcount: 1
2867 { lat: 30, common_pid: 2302 } hitcount: 4
2868 { lat: 31, common_pid: 2302 } hitcount: 6
2869 { lat: 32, common_pid: 2302 } hitcount: 1
2870 { lat: 33, common_pid: 2299 } hitcount: 1
2871 { lat: 33, common_pid: 2302 } hitcount: 3
2872 { lat: 34, common_pid: 2302 } hitcount: 2
2873 { lat: 35, common_pid: 2302 } hitcount: 1
2874 { lat: 35, common_pid: 2304 } hitcount: 1
2875 { lat: 36, common_pid: 2302 } hitcount: 4
2876 { lat: 37, common_pid: 2302 } hitcount: 6
2877 { lat: 38, common_pid: 2302 } hitcount: 2
2878 { lat: 39, common_pid: 2302 } hitcount: 2
2879 { lat: 39, common_pid: 2304 } hitcount: 1
2880 { lat: 40, common_pid: 2304 } hitcount: 2
2881 { lat: 40, common_pid: 2302 } hitcount: 5
2882 { lat: 41, common_pid: 2304 } hitcount: 1
2883 { lat: 41, common_pid: 2302 } hitcount: 8
2884 { lat: 42, common_pid: 2302 } hitcount: 6
2885 { lat: 42, common_pid: 2304 } hitcount: 1
2886 { lat: 43, common_pid: 2302 } hitcount: 3
2887 { lat: 43, common_pid: 2304 } hitcount: 4
2888 { lat: 44, common_pid: 2302 } hitcount: 6
2889 { lat: 45, common_pid: 2302 } hitcount: 5
2890 { lat: 46, common_pid: 2302 } hitcount: 5
2891 { lat: 47, common_pid: 2302 } hitcount: 7
2892 { lat: 48, common_pid: 2301 } hitcount: 1
2893 { lat: 48, common_pid: 2302 } hitcount: 9
2894 { lat: 49, common_pid: 2302 } hitcount: 3
2895 { lat: 50, common_pid: 2302 } hitcount: 1
2896 { lat: 50, common_pid: 2301 } hitcount: 1
2897 { lat: 51, common_pid: 2302 } hitcount: 2
2898 { lat: 51, common_pid: 2301 } hitcount: 1
2899 { lat: 61, common_pid: 2302 } hitcount: 1
2900 { lat: 110, common_pid: 2302 } hitcount: 1
2901
2902 Totals:
2903 Hits: 89565
2904 Entries: 158
2905 Dropped: 0
2906
2907 This doesn't tell us any information about how late cyclictest may have
2908 woken up, but it does show us a nice histogram of how long it took from
2909 the time that cyclictest was woken to the time it made it into user space.
