1================ 2Event Histograms 3================ 4 5Documentation written by Tom Zanussi 6 71. Introduction 8=============== 9 10 Histogram triggers are special event triggers that can be used to 11 aggregate trace event data into histograms. For information on 12 trace events and event triggers, see Documentation/trace/events.rst. 13 14 152. Histogram Trigger Command 16============================ 17 18 A histogram trigger command is an event trigger command that 19 aggregates event hits into a hash table keyed on one or more trace 20 event format fields (or stacktrace) and a set of running totals 21 derived from one or more trace event format fields and/or event 22 counts (hitcount). 23 24 The format of a hist trigger is as follows:: 25 26 hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>] 27 [:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue] 28 [:clear][:name=histname1][:nohitcount][:<handler>.<action>] [if <filter>] 29 30 When a matching event is hit, an entry is added to a hash table 31 using the key(s) and value(s) named. Keys and values correspond to 32 fields in the event's format description. Values must correspond to 33 numeric fields - on an event hit, the value(s) will be added to a 34 sum kept for that field. The special string 'hitcount' can be used 35 in place of an explicit value field - this is simply a count of 36 event hits. If 'values' isn't specified, an implicit 'hitcount' 37 value will be automatically created and used as the only value. 38 Keys can be any field, or the special string 'common_stacktrace', which 39 will use the event's kernel stacktrace as the key. The keywords 40 'keys' or 'key' can be used to specify keys, and the keywords 41 'values', 'vals', or 'val' can be used to specify values. Compound 42 keys consisting of up to three fields can be specified by the 'keys' 43 keyword. Hashing a compound key produces a unique entry in the 44 table for each unique combination of component keys, and can be 45 useful for providing more fine-grained summaries of event data. 46 Additionally, sort keys consisting of up to two fields can be 47 specified by the 'sort' keyword. If more than one field is 48 specified, the result will be a 'sort within a sort': the first key 49 is taken to be the primary sort key and the second the secondary 50 key. If a hist trigger is given a name using the 'name' parameter, 51 its histogram data will be shared with other triggers of the same 52 name, and trigger hits will update this common data. Only triggers 53 with 'compatible' fields can be combined in this way; triggers are 54 'compatible' if the fields named in the trigger share the same 55 number and type of fields and those fields also have the same names. 56 Note that any two events always share the compatible 'hitcount' and 57 'common_stacktrace' fields and can therefore be combined using those 58 fields, however pointless that may be. 59 60 'hist' triggers add a 'hist' file to each event's subdirectory. 61 Reading the 'hist' file for the event will dump the hash table in 62 its entirety to stdout. If there are multiple hist triggers 63 attached to an event, there will be a table for each trigger in the 64 output. The table displayed for a named trigger will be the same as 65 any other instance having the same name. Each printed hash table 66 entry is a simple list of the keys and values comprising the entry; 67 keys are printed first and are delineated by curly braces, and are 68 followed by the set of value fields for the entry. By default, 69 numeric fields are displayed as base-10 integers. This can be 70 modified by appending any of the following modifiers to the field 71 name: 72 73 ============= ================================================= 74 .hex display a number as a hex value 75 .sym display an address as a symbol 76 .sym-offset display an address as a symbol and offset 77 .syscall display a syscall id as a system call name 78 .execname display a common_pid as a program name 79 .log2 display log2 value rather than raw number 80 .buckets=size display grouping of values rather than raw number 81 .usecs display a common_timestamp in microseconds 82 .percent display a number of percentage value 83 .graph display a bar-graph of a value 84 .stacktrace display as a stacktrace (must by a long[] type) 85 ============= ================================================= 86 87 Note that in general the semantics of a given field aren't 88 interpreted when applying a modifier to it, but there are some 89 restrictions to be aware of in this regard: 90 91 - only the 'hex' modifier can be used for values (because values 92 are essentially sums, and the other modifiers don't make sense 93 in that context). 94 - the 'execname' modifier can only be used on a 'common_pid'. The 95 reason for this is that the execname is simply the 'comm' value 96 saved for the 'current' process when an event was triggered, 97 which is the same as the common_pid value saved by the event 98 tracing code. Trying to apply that comm value to other pid 99 values wouldn't be correct, and typically events that care save 100 pid-specific comm fields in the event itself. 101 102 A typical usage scenario would be the following to enable a hist 103 trigger, read its current contents, and then turn it off:: 104 105 # echo 'hist:keys=skbaddr.hex:vals=len' > \ 106 /sys/kernel/tracing/events/net/netif_rx/trigger 107 108 # cat /sys/kernel/tracing/events/net/netif_rx/hist 109 110 # echo '!hist:keys=skbaddr.hex:vals=len' > \ 111 /sys/kernel/tracing/events/net/netif_rx/trigger 112 113 The trigger file itself can be read to show the details of the 114 currently attached hist trigger. This information is also displayed 115 at the top of the 'hist' file when read. 116 117 By default, the size of the hash table is 2048 entries. The 'size' 118 parameter can be used to specify more or fewer than that. The units 119 are in terms of hashtable entries - if a run uses more entries than 120 specified, the results will show the number of 'drops', the number 121 of hits that were ignored. The size should be a power of 2 between 122 128 and 131072 (any non- power-of-2 number specified will be rounded 123 up). 124 125 The 'sort' parameter can be used to specify a value field to sort 126 on. The default if unspecified is 'hitcount' and the default sort 127 order is 'ascending'. To sort in the opposite direction, append 128 .descending' to the sort key. 129 130 The 'pause' parameter can be used to pause an existing hist trigger 131 or to start a hist trigger but not log any events until told to do 132 so. 'continue' or 'cont' can be used to start or restart a paused 133 hist trigger. 134 135 The 'clear' parameter will clear the contents of a running hist 136 trigger and leave its current paused/active state. 137 138 Note that the 'pause', 'cont', and 'clear' parameters should be 139 applied using 'append' shell operator ('>>') if applied to an 140 existing trigger, rather than via the '>' operator, which will cause 141 the trigger to be removed through truncation. 142 143 The 'nohitcount' (or NOHC) parameter will suppress display of 144 raw hitcount in the histogram. This option requires at least one 145 value field which is not a 'raw hitcount'. For example, 146 'hist:...:vals=hitcount:nohitcount' is rejected, but 147 'hist:...:vals=hitcount.percent:nohitcount' is OK. 148 149- enable_hist/disable_hist 150 151 The enable_hist and disable_hist triggers can be used to have one 152 event conditionally start and stop another event's already-attached 153 hist trigger. Any number of enable_hist and disable_hist triggers 154 can be attached to a given event, allowing that event to kick off 155 and stop aggregations on a host of other events. 156 157 The format is very similar to the enable/disable_event triggers:: 158 159 enable_hist:<system>:<event>[:count] 160 disable_hist:<system>:<event>[:count] 161 162 Instead of enabling or disabling the tracing of the target event 163 into the trace buffer as the enable/disable_event triggers do, the 164 enable/disable_hist triggers enable or disable the aggregation of 165 the target event into a hash table. 166 167 A typical usage scenario for the enable_hist/disable_hist triggers 168 would be to first set up a paused hist trigger on some event, 169 followed by an enable_hist/disable_hist pair that turns the hist 170 aggregation on and off when conditions of interest are hit:: 171 172 # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \ 173 /sys/kernel/tracing/events/net/netif_receive_skb/trigger 174 175 # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \ 176 /sys/kernel/tracing/events/sched/sched_process_exec/trigger 177 178 # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \ 179 /sys/kernel/tracing/events/sched/sched_process_exit/trigger 180 181 The above sets up an initially paused hist trigger which is unpaused 182 and starts aggregating events when a given program is executed, and 183 which stops aggregating when the process exits and the hist trigger 184 is paused again. 185 186 The examples below provide a more concrete illustration of the 187 concepts and typical usage patterns discussed above. 188 189'special' event fields 190------------------------ 191 192 There are a number of 'special event fields' available for use as 193 keys or values in a hist trigger. These look like and behave as if 194 they were actual event fields, but aren't really part of the event's 195 field definition or format file. They are however available for any 196 event, and can be used anywhere an actual event field could be. 197 They are: 198 199 ====================== ==== ======================================= 200 common_timestamp u64 timestamp (from ring buffer) associated 201 with the event, in nanoseconds. May be 202 modified by .usecs to have timestamps 203 interpreted as microseconds. 204 common_cpu int the cpu on which the event occurred. 205 ====================== ==== ======================================= 206 207Extended error information 208-------------------------- 209 210 For some error conditions encountered when invoking a hist trigger 211 command, extended error information is available via the 212 tracing/error_log file. See Error Conditions in 213 :file:`Documentation/trace/ftrace.rst` for details. 214 2156.2 'hist' trigger examples 216--------------------------- 217 218 The first set of examples creates aggregations using the kmalloc 219 event. The fields that can be used for the hist trigger are listed 220 in the kmalloc event's format file:: 221 222 # cat /sys/kernel/tracing/events/kmem/kmalloc/format 223 name: kmalloc 224 ID: 374 225 format: 226 field:unsigned short common_type; offset:0; size:2; signed:0; 227 field:unsigned char common_flags; offset:2; size:1; signed:0; 228 field:unsigned char common_preempt_count; offset:3; size:1; signed:0; 229 field:int common_pid; offset:4; size:4; signed:1; 230 231 field:unsigned long call_site; offset:8; size:8; signed:0; 232 field:const void * ptr; offset:16; size:8; signed:0; 233 field:size_t bytes_req; offset:24; size:8; signed:0; 234 field:size_t bytes_alloc; offset:32; size:8; signed:0; 235 field:gfp_t gfp_flags; offset:40; size:4; signed:0; 236 237 We'll start by creating a hist trigger that generates a simple table 238 that lists the total number of bytes requested for each function in 239 the kernel that made one or more calls to kmalloc:: 240 241 # echo 'hist:key=call_site:val=bytes_req.buckets=32' > \ 242 /sys/kernel/tracing/events/kmem/kmalloc/trigger 243 244 This tells the tracing system to create a 'hist' trigger using the 245 call_site field of the kmalloc event as the key for the table, which 246 just means that each unique call_site address will have an entry 247 created for it in the table. The 'val=bytes_req' parameter tells 248 the hist trigger that for each unique entry (call_site) in the 249 table, it should keep a running total of the number of bytes 250 requested by that call_site. 251 252 We'll let it run for awhile and then dump the contents of the 'hist' 253 file in the kmalloc event's subdirectory (for readability, a number 254 of entries have been omitted):: 255 256 # cat /sys/kernel/tracing/events/kmem/kmalloc/hist 257 # trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active] 258 259 { call_site: 18446744072106379007 } hitcount: 1 bytes_req: 176 260 { call_site: 18446744071579557049 } hitcount: 1 bytes_req: 1024 261 { call_site: 18446744071580608289 } hitcount: 1 bytes_req: 16384 262 { call_site: 18446744071581827654 } hitcount: 1 bytes_req: 24 263 { call_site: 18446744071580700980 } hitcount: 1 bytes_req: 8 264 { call_site: 18446744071579359876 } hitcount: 1 bytes_req: 152 265 { call_site: 18446744071580795365 } hitcount: 3 bytes_req: 144 266 { call_site: 18446744071581303129 } hitcount: 3 bytes_req: 144 267 { call_site: 18446744071580713234 } hitcount: 4 bytes_req: 2560 268 { call_site: 18446744071580933750 } hitcount: 4 bytes_req: 736 269 . 270 . 271 . 272 { call_site: 18446744072106047046 } hitcount: 69 bytes_req: 5576 273 { call_site: 18446744071582116407 } hitcount: 73 bytes_req: 2336 274 { call_site: 18446744072106054684 } hitcount: 136 bytes_req: 140504 275 { call_site: 18446744072106224230 } hitcount: 136 bytes_req: 19584 276 { call_site: 18446744072106078074 } hitcount: 153 bytes_req: 2448 277 { call_site: 18446744072106062406 } hitcount: 153 bytes_req: 36720 278 { call_site: 18446744071582507929 } hitcount: 153 bytes_req: 37088 279 { call_site: 18446744072102520590 } hitcount: 273 bytes_req: 10920 280 { call_site: 18446744071582143559 } hitcount: 358 bytes_req: 716 281 { call_site: 18446744072106465852 } hitcount: 417 bytes_req: 56712 282 { call_site: 18446744072102523378 } hitcount: 485 bytes_req: 27160 283 { call_site: 18446744072099568646 } hitcount: 1676 bytes_req: 33520 284 285 Totals: 286 Hits: 4610 287 Entries: 45 288 Dropped: 0 289 290 The output displays a line for each entry, beginning with the key 291 specified in the trigger, followed by the value(s) also specified in 292 the trigger. At the beginning of the output is a line that displays 293 the trigger info, which can also be displayed by reading the 294 'trigger' file:: 295 296 # cat /sys/kernel/tracing/events/kmem/kmalloc/trigger 297 hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active] 298 299 At the end of the output are a few lines that display the overall 300 totals for the run. The 'Hits' field shows the total number of 301 times the event trigger was hit, the 'Entries' field shows the total 302 number of used entries in the hash table, and the 'Dropped' field 303 shows the number of hits that were dropped because the number of 304 used entries for the run exceeded the maximum number of entries 305 allowed for the table (normally 0, but if not a hint that you may 306 want to increase the size of the table using the 'size' parameter). 307 308 Notice in the above output that there's an extra field, 'hitcount', 309 which wasn't specified in the trigger. Also notice that in the 310 trigger info output, there's a parameter, 'sort=hitcount', which 311 wasn't specified in the trigger either. The reason for that is that 312 every trigger implicitly keeps a count of the total number of hits 313 attributed to a given entry, called the 'hitcount'. That hitcount 314 information is explicitly displayed in the output, and in the 315 absence of a user-specified sort parameter, is used as the default 316 sort field. 317 318 The value 'hitcount' can be used in place of an explicit value in 319 the 'values' parameter if you don't really need to have any 320 particular field summed and are mainly interested in hit 321 frequencies. 322 323 To turn the hist trigger off, simply call up the trigger in the 324 command history and re-execute it with a '!' prepended:: 325 326 # echo '!hist:key=call_site:val=bytes_req' > \ 327 /sys/kernel/tracing/events/kmem/kmalloc/trigger 328 329 Finally, notice that the call_site as displayed in the output above 330 isn't really very useful. It's an address, but normally addresses 331 are displayed in hex. To have a numeric field displayed as a hex 332 value, simply append '.hex' to the field name in the trigger:: 333 334 # echo 'hist:key=call_site.hex:val=bytes_req' > \ 335 /sys/kernel/tracing/events/kmem/kmalloc/trigger 336 337 # cat /sys/kernel/tracing/events/kmem/kmalloc/hist 338 # trigger info: hist:keys=call_site.hex:vals=bytes_req:sort=hitcount:size=2048 [active] 339 340 { call_site: ffffffffa026b291 } hitcount: 1 bytes_req: 433 341 { call_site: ffffffffa07186ff } hitcount: 1 bytes_req: 176 342 { call_site: ffffffff811ae721 } hitcount: 1 bytes_req: 16384 343 { call_site: ffffffff811c5134 } hitcount: 1 bytes_req: 8 344 { call_site: ffffffffa04a9ebb } hitcount: 1 bytes_req: 511 345 { call_site: ffffffff8122e0a6 } hitcount: 1 bytes_req: 12 346 { call_site: ffffffff8107da84 } hitcount: 1 bytes_req: 152 347 { call_site: ffffffff812d8246 } hitcount: 1 bytes_req: 24 348 { call_site: ffffffff811dc1e5 } hitcount: 3 bytes_req: 144 349 { call_site: ffffffffa02515e8 } hitcount: 3 bytes_req: 648 350 { call_site: ffffffff81258159 } hitcount: 3 bytes_req: 144 351 { call_site: ffffffff811c80f4 } hitcount: 4 bytes_req: 544 352 . 353 . 354 . 355 { call_site: ffffffffa06c7646 } hitcount: 106 bytes_req: 8024 356 { call_site: ffffffffa06cb246 } hitcount: 132 bytes_req: 31680 357 { call_site: ffffffffa06cef7a } hitcount: 132 bytes_req: 2112 358 { call_site: ffffffff8137e399 } hitcount: 132 bytes_req: 23232 359 { call_site: ffffffffa06c941c } hitcount: 185 bytes_req: 171360 360 { call_site: ffffffffa06f2a66 } hitcount: 185 bytes_req: 26640 361 { call_site: ffffffffa036a70e } hitcount: 265 bytes_req: 10600 362 { call_site: ffffffff81325447 } hitcount: 292 bytes_req: 584 363 { call_site: ffffffffa072da3c } hitcount: 446 bytes_req: 60656 364 { call_site: ffffffffa036b1f2 } hitcount: 526 bytes_req: 29456 365 { call_site: ffffffffa0099c06 } hitcount: 1780 bytes_req: 35600 366 367 Totals: 368 Hits: 4775 369 Entries: 46 370 Dropped: 0 371 372 Even that's only marginally more useful - while hex values do look 373 more like addresses, what users are typically more interested in 374 when looking at text addresses are the corresponding symbols 375 instead. To have an address displayed as symbolic value instead, 376 simply append '.sym' or '.sym-offset' to the field name in the 377 trigger:: 378 379 # echo 'hist:key=call_site.sym:val=bytes_req' > \ 380 /sys/kernel/tracing/events/kmem/kmalloc/trigger 381 382 # cat /sys/kernel/tracing/events/kmem/kmalloc/hist 383 # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=hitcount:size=2048 [active] 384 385 { call_site: [ffffffff810adcb9] syslog_print_all } hitcount: 1 bytes_req: 1024 386 { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 387 { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 388 { call_site: [ffffffff8154acbe] usb_alloc_urb } hitcount: 1 bytes_req: 192 389 { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 390 { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40 391 { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 392 { call_site: [ffffffff811febd5] fsnotify_alloc_group } hitcount: 2 bytes_req: 528 393 { call_site: [ffffffff81440f58] __tty_buffer_request_room } hitcount: 2 bytes_req: 2624 394 { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 2 bytes_req: 96 395 { call_site: [ffffffffa05e19af] ieee80211_start_tx_ba_session [mac80211] } hitcount: 2 bytes_req: 464 396 { call_site: [ffffffff81672406] tcp_get_metrics } hitcount: 2 bytes_req: 304 397 { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 398 { call_site: [ffffffff81089b05] sched_create_group } hitcount: 2 bytes_req: 1424 399 . 400 . 401 . 402 { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1185 bytes_req: 123240 403 { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 1185 bytes_req: 104280 404 { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 1402 bytes_req: 190672 405 { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 1518 bytes_req: 146208 406 { call_site: [ffffffffa029070e] drm_vma_node_allow [drm] } hitcount: 1746 bytes_req: 69840 407 { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 2021 bytes_req: 792312 408 { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 2592 bytes_req: 145152 409 { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2629 bytes_req: 378576 410 { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2629 bytes_req: 3783248 411 { call_site: [ffffffff81325607] apparmor_file_alloc_security } hitcount: 5192 bytes_req: 10384 412 { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 5529 bytes_req: 110584 413 { call_site: [ffffffff8131ebf7] aa_alloc_task_context } hitcount: 21943 bytes_req: 702176 414 { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 55759 bytes_req: 5074265 415 416 Totals: 417 Hits: 109928 418 Entries: 71 419 Dropped: 0 420 421 Because the default sort key above is 'hitcount', the above shows a 422 the list of call_sites by increasing hitcount, so that at the bottom 423 we see the functions that made the most kmalloc calls during the 424 run. If instead we wanted to see the top kmalloc callers in 425 terms of the number of bytes requested rather than the number of 426 calls, and we wanted the top caller to appear at the top, we can use 427 the 'sort' parameter, along with the 'descending' modifier:: 428 429 # echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \ 430 /sys/kernel/tracing/events/kmem/kmalloc/trigger 431 432 # cat /sys/kernel/tracing/events/kmem/kmalloc/hist 433 # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=bytes_req.descending:size=2048 [active] 434 435 { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2186 bytes_req: 3397464 436 { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1790 bytes_req: 712176 437 { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 8132 bytes_req: 513135 438 { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 106 bytes_req: 440128 439 { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2186 bytes_req: 314784 440 { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 2174 bytes_req: 208992 441 { call_site: [ffffffff811ae8e1] __kmalloc } hitcount: 8 bytes_req: 131072 442 { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 859 bytes_req: 116824 443 { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 1834 bytes_req: 102704 444 { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 972 bytes_req: 101088 445 { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 972 bytes_req: 85536 446 { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 3333 bytes_req: 66664 447 { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 209 bytes_req: 61632 448 . 449 . 450 . 451 { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 452 { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 453 { call_site: [ffffffff812d8406] copy_semundo } hitcount: 2 bytes_req: 48 454 { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 1 bytes_req: 48 455 { call_site: [ffffffffa027121a] drm_getmagic [drm] } hitcount: 1 bytes_req: 48 456 { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40 457 { call_site: [ffffffff811c52f4] bprm_change_interp } hitcount: 2 bytes_req: 16 458 { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 459 { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 460 { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 461 462 Totals: 463 Hits: 32133 464 Entries: 81 465 Dropped: 0 466 467 To display the offset and size information in addition to the symbol 468 name, just use 'sym-offset' instead:: 469 470 # echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \ 471 /sys/kernel/tracing/events/kmem/kmalloc/trigger 472 473 # cat /sys/kernel/tracing/events/kmem/kmalloc/hist 474 # trigger info: hist:keys=call_site.sym-offset:vals=bytes_req:sort=bytes_req.descending:size=2048 [active] 475 476 { call_site: [ffffffffa046041c] i915_gem_execbuffer2+0x6c/0x2c0 [i915] } hitcount: 4569 bytes_req: 3163720 477 { call_site: [ffffffffa0489a66] intel_ring_begin+0xc6/0x1f0 [i915] } hitcount: 4569 bytes_req: 657936 478 { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23+0x694/0x1020 [i915] } hitcount: 1519 bytes_req: 472936 479 { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23+0x516/0x1020 [i915] } hitcount: 3050 bytes_req: 211832 480 { call_site: [ffffffff811e2a1b] seq_buf_alloc+0x1b/0x50 } hitcount: 34 bytes_req: 148384 481 { call_site: [ffffffffa04a580c] intel_crtc_page_flip+0xbc/0x870 [i915] } hitcount: 1385 bytes_req: 144040 482 { call_site: [ffffffff811ae8e1] __kmalloc+0x191/0x1b0 } hitcount: 8 bytes_req: 131072 483 { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl+0x282/0x360 [drm] } hitcount: 1385 bytes_req: 121880 484 { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc+0x32/0x100 [drm] } hitcount: 1848 bytes_req: 103488 485 { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state+0x2c/0xa0 [i915] } hitcount: 461 bytes_req: 62696 486 { call_site: [ffffffffa029070e] drm_vma_node_allow+0x2e/0xd0 [drm] } hitcount: 1541 bytes_req: 61640 487 { call_site: [ffffffff815f8d7b] sk_prot_alloc+0xcb/0x1b0 } hitcount: 57 bytes_req: 57456 488 . 489 . 490 . 491 { call_site: [ffffffff8109524a] alloc_fair_sched_group+0x5a/0x1a0 } hitcount: 2 bytes_req: 128 492 { call_site: [ffffffffa027b921] drm_vm_open_locked+0x31/0xa0 [drm] } hitcount: 3 bytes_req: 96 493 { call_site: [ffffffff8122e266] proc_self_follow_link+0x76/0xb0 } hitcount: 8 bytes_req: 96 494 { call_site: [ffffffff81213e80] load_elf_binary+0x240/0x1650 } hitcount: 3 bytes_req: 84 495 { call_site: [ffffffff8154bc62] usb_control_msg+0x42/0x110 } hitcount: 1 bytes_req: 8 496 { call_site: [ffffffffa00bf6fe] hidraw_send_report+0x7e/0x1a0 [hid] } hitcount: 1 bytes_req: 7 497 { call_site: [ffffffffa00bf1ca] hidraw_report_event+0x8a/0x120 [hid] } hitcount: 1 bytes_req: 7 498 499 Totals: 500 Hits: 26098 501 Entries: 64 502 Dropped: 0 503 504 We can also add multiple fields to the 'values' parameter. For 505 example, we might want to see the total number of bytes allocated 506 alongside bytes requested, and display the result sorted by bytes 507 allocated in a descending order:: 508 509 # echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \ 510 /sys/kernel/tracing/events/kmem/kmalloc/trigger 511 512 # cat /sys/kernel/tracing/events/kmem/kmalloc/hist 513 # trigger info: hist:keys=call_site.sym:vals=bytes_req,bytes_alloc:sort=bytes_alloc.descending:size=2048 [active] 514 515 { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 7403 bytes_req: 4084360 bytes_alloc: 5958016 516 { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 541 bytes_req: 2213968 bytes_alloc: 2228224 517 { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 7404 bytes_req: 1066176 bytes_alloc: 1421568 518 { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1565 bytes_req: 557368 bytes_alloc: 1037760 519 { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 9557 bytes_req: 595778 bytes_alloc: 695744 520 { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 5839 bytes_req: 430680 bytes_alloc: 470400 521 { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 2388 bytes_req: 324768 bytes_alloc: 458496 522 { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 3911 bytes_req: 219016 bytes_alloc: 250304 523 { call_site: [ffffffff815f8d7b] sk_prot_alloc } hitcount: 235 bytes_req: 236880 bytes_alloc: 240640 524 { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 557 bytes_req: 169024 bytes_alloc: 221760 525 { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 9378 bytes_req: 187548 bytes_alloc: 206312 526 { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1519 bytes_req: 157976 bytes_alloc: 194432 527 . 528 . 529 . 530 { call_site: [ffffffff8109bd3b] sched_autogroup_create_attach } hitcount: 2 bytes_req: 144 bytes_alloc: 192 531 { call_site: [ffffffff81097ee8] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128 532 { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128 533 { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128 534 { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128 535 { call_site: [ffffffff81213e80] load_elf_binary } hitcount: 3 bytes_req: 84 bytes_alloc: 96 536 { call_site: [ffffffff81079a2e] kthread_create_on_node } hitcount: 1 bytes_req: 56 bytes_alloc: 64 537 { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8 538 { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 bytes_alloc: 8 539 { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8 540 541 Totals: 542 Hits: 66598 543 Entries: 65 544 Dropped: 0 545 546 Finally, to finish off our kmalloc example, instead of simply having 547 the hist trigger display symbolic call_sites, we can have the hist 548 trigger additionally display the complete set of kernel stack traces 549 that led to each call_site. To do that, we simply use the special 550 value 'common_stacktrace' for the key parameter:: 551 552 # echo 'hist:keys=common_stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \ 553 /sys/kernel/tracing/events/kmem/kmalloc/trigger 554 555 The above trigger will use the kernel stack trace in effect when an 556 event is triggered as the key for the hash table. This allows the 557 enumeration of every kernel callpath that led up to a particular 558 event, along with a running total of any of the event fields for 559 that event. Here we tally bytes requested and bytes allocated for 560 every callpath in the system that led up to a kmalloc (in this case 561 every callpath to a kmalloc for a kernel compile):: 562 563 # cat /sys/kernel/tracing/events/kmem/kmalloc/hist 564 # trigger info: hist:keys=common_stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active] 565 566 { common_stacktrace: 567 __kmalloc_track_caller+0x10b/0x1a0 568 kmemdup+0x20/0x50 569 hidraw_report_event+0x8a/0x120 [hid] 570 hid_report_raw_event+0x3ea/0x440 [hid] 571 hid_input_report+0x112/0x190 [hid] 572 hid_irq_in+0xc2/0x260 [usbhid] 573 __usb_hcd_giveback_urb+0x72/0x120 574 usb_giveback_urb_bh+0x9e/0xe0 575 tasklet_hi_action+0xf8/0x100 576 __do_softirq+0x114/0x2c0 577 irq_exit+0xa5/0xb0 578 do_IRQ+0x5a/0xf0 579 ret_from_intr+0x0/0x30 580 cpuidle_enter+0x17/0x20 581 cpu_startup_entry+0x315/0x3e0 582 rest_init+0x7c/0x80 583 } hitcount: 3 bytes_req: 21 bytes_alloc: 24 584 { common_stacktrace: 585 __kmalloc_track_caller+0x10b/0x1a0 586 kmemdup+0x20/0x50 587 hidraw_report_event+0x8a/0x120 [hid] 588 hid_report_raw_event+0x3ea/0x440 [hid] 589 hid_input_report+0x112/0x190 [hid] 590 hid_irq_in+0xc2/0x260 [usbhid] 591 __usb_hcd_giveback_urb+0x72/0x120 592 usb_giveback_urb_bh+0x9e/0xe0 593 tasklet_hi_action+0xf8/0x100 594 __do_softirq+0x114/0x2c0 595 irq_exit+0xa5/0xb0 596 do_IRQ+0x5a/0xf0 597 ret_from_intr+0x0/0x30 598 } hitcount: 3 bytes_req: 21 bytes_alloc: 24 599 { common_stacktrace: 600 kmem_cache_alloc_trace+0xeb/0x150 601 aa_alloc_task_context+0x27/0x40 602 apparmor_cred_prepare+0x1f/0x50 603 security_prepare_creds+0x16/0x20 604 prepare_creds+0xdf/0x1a0 605 SyS_capset+0xb5/0x200 606 system_call_fastpath+0x12/0x6a 607 } hitcount: 1 bytes_req: 32 bytes_alloc: 32 608 . 609 . 610 . 611 { common_stacktrace: 612 __kmalloc+0x11b/0x1b0 613 i915_gem_execbuffer2+0x6c/0x2c0 [i915] 614 drm_ioctl+0x349/0x670 [drm] 615 do_vfs_ioctl+0x2f0/0x4f0 616 SyS_ioctl+0x81/0xa0 617 system_call_fastpath+0x12/0x6a 618 } hitcount: 17726 bytes_req: 13944120 bytes_alloc: 19593808 619 { common_stacktrace: 620 __kmalloc+0x11b/0x1b0 621 load_elf_phdrs+0x76/0xa0 622 load_elf_binary+0x102/0x1650 623 search_binary_handler+0x97/0x1d0 624 do_execveat_common.isra.34+0x551/0x6e0 625 SyS_execve+0x3a/0x50 626 return_from_execve+0x0/0x23 627 } hitcount: 33348 bytes_req: 17152128 bytes_alloc: 20226048 628 { common_stacktrace: 629 kmem_cache_alloc_trace+0xeb/0x150 630 apparmor_file_alloc_security+0x27/0x40 631 security_file_alloc+0x16/0x20 632 get_empty_filp+0x93/0x1c0 633 path_openat+0x31/0x5f0 634 do_filp_open+0x3a/0x90 635 do_sys_open+0x128/0x220 636 SyS_open+0x1e/0x20 637 system_call_fastpath+0x12/0x6a 638 } hitcount: 4766422 bytes_req: 9532844 bytes_alloc: 38131376 639 { common_stacktrace: 640 __kmalloc+0x11b/0x1b0 641 seq_buf_alloc+0x1b/0x50 642 seq_read+0x2cc/0x370 643 proc_reg_read+0x3d/0x80 644 __vfs_read+0x28/0xe0 645 vfs_read+0x86/0x140 646 SyS_read+0x46/0xb0 647 system_call_fastpath+0x12/0x6a 648 } hitcount: 19133 bytes_req: 78368768 bytes_alloc: 78368768 649 650 Totals: 651 Hits: 6085872 652 Entries: 253 653 Dropped: 0 654 655 If you key a hist trigger on common_pid, in order for example to 656 gather and display sorted totals for each process, you can use the 657 special .execname modifier to display the executable names for the 658 processes in the table rather than raw pids. The example below 659 keeps a per-process sum of total bytes read:: 660 661 # echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \ 662 /sys/kernel/tracing/events/syscalls/sys_enter_read/trigger 663 664 # cat /sys/kernel/tracing/events/syscalls/sys_enter_read/hist 665 # trigger info: hist:keys=common_pid.execname:vals=count:sort=count.descending:size=2048 [active] 666 667 { common_pid: gnome-terminal [ 3196] } hitcount: 280 count: 1093512 668 { common_pid: Xorg [ 1309] } hitcount: 525 count: 256640 669 { common_pid: compiz [ 2889] } hitcount: 59 count: 254400 670 { common_pid: bash [ 8710] } hitcount: 3 count: 66369 671 { common_pid: dbus-daemon-lau [ 8703] } hitcount: 49 count: 47739 672 { common_pid: irqbalance [ 1252] } hitcount: 27 count: 27648 673 { common_pid: 01ifupdown [ 8705] } hitcount: 3 count: 17216 674 { common_pid: dbus-daemon [ 772] } hitcount: 10 count: 12396 675 { common_pid: Socket Thread [ 8342] } hitcount: 11 count: 11264 676 { common_pid: nm-dhcp-client. [ 8701] } hitcount: 6 count: 7424 677 { common_pid: gmain [ 1315] } hitcount: 18 count: 6336 678 . 679 . 680 . 681 { common_pid: postgres [ 1892] } hitcount: 2 count: 32 682 { common_pid: postgres [ 1891] } hitcount: 2 count: 32 683 { common_pid: gmain [ 8704] } hitcount: 2 count: 32 684 { common_pid: upstart-dbus-br [ 2740] } hitcount: 21 count: 21 685 { common_pid: nm-dispatcher.a [ 8696] } hitcount: 1 count: 16 686 { common_pid: indicator-datet [ 2904] } hitcount: 1 count: 16 687 { common_pid: gdbus [ 2998] } hitcount: 1 count: 16 688 { common_pid: rtkit-daemon [ 2052] } hitcount: 1 count: 8 689 { common_pid: init [ 1] } hitcount: 2 count: 2 690 691 Totals: 692 Hits: 2116 693 Entries: 51 694 Dropped: 0 695 696 Similarly, if you key a hist trigger on syscall id, for example to 697 gather and display a list of systemwide syscall hits, you can use 698 the special .syscall modifier to display the syscall names rather 699 than raw ids. The example below keeps a running total of syscall 700 counts for the system during the run:: 701 702 # echo 'hist:key=id.syscall:val=hitcount' > \ 703 /sys/kernel/tracing/events/raw_syscalls/sys_enter/trigger 704 705 # cat /sys/kernel/tracing/events/raw_syscalls/sys_enter/hist 706 # trigger info: hist:keys=id.syscall:vals=hitcount:sort=hitcount:size=2048 [active] 707 708 { id: sys_fsync [ 74] } hitcount: 1 709 { id: sys_newuname [ 63] } hitcount: 1 710 { id: sys_prctl [157] } hitcount: 1 711 { id: sys_statfs [137] } hitcount: 1 712 { id: sys_symlink [ 88] } hitcount: 1 713 { id: sys_sendmmsg [307] } hitcount: 1 714 { id: sys_semctl [ 66] } hitcount: 1 715 { id: sys_readlink [ 89] } hitcount: 3 716 { id: sys_bind [ 49] } hitcount: 3 717 { id: sys_getsockname [ 51] } hitcount: 3 718 { id: sys_unlink [ 87] } hitcount: 3 719 { id: sys_rename [ 82] } hitcount: 4 720 { id: unknown_syscall [ 58] } hitcount: 4 721 { id: sys_connect [ 42] } hitcount: 4 722 { id: sys_getpid [ 39] } hitcount: 4 723 . 724 . 725 . 726 { id: sys_rt_sigprocmask [ 14] } hitcount: 952 727 { id: sys_futex [202] } hitcount: 1534 728 { id: sys_write [ 1] } hitcount: 2689 729 { id: sys_setitimer [ 38] } hitcount: 2797 730 { id: sys_read [ 0] } hitcount: 3202 731 { id: sys_select [ 23] } hitcount: 3773 732 { id: sys_writev [ 20] } hitcount: 4531 733 { id: sys_poll [ 7] } hitcount: 8314 734 { id: sys_recvmsg [ 47] } hitcount: 13738 735 { id: sys_ioctl [ 16] } hitcount: 21843 736 737 Totals: 738 Hits: 67612 739 Entries: 72 740 Dropped: 0 741 742 The syscall counts above provide a rough overall picture of system 743 call activity on the system; we can see for example that the most 744 popular system call on this system was the 'sys_ioctl' system call. 745 746 We can use 'compound' keys to refine that number and provide some 747 further insight as to which processes exactly contribute to the 748 overall ioctl count. 749 750 The command below keeps a hitcount for every unique combination of 751 system call id and pid - the end result is essentially a table 752 that keeps a per-pid sum of system call hits. The results are 753 sorted using the system call id as the primary key, and the 754 hitcount sum as the secondary key:: 755 756 # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \ 757 /sys/kernel/tracing/events/raw_syscalls/sys_enter/trigger 758 759 # cat /sys/kernel/tracing/events/raw_syscalls/sys_enter/hist 760 # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active] 761 762 { id: sys_read [ 0], common_pid: rtkit-daemon [ 1877] } hitcount: 1 763 { id: sys_read [ 0], common_pid: gdbus [ 2976] } hitcount: 1 764 { id: sys_read [ 0], common_pid: console-kit-dae [ 3400] } hitcount: 1 765 { id: sys_read [ 0], common_pid: postgres [ 1865] } hitcount: 1 766 { id: sys_read [ 0], common_pid: deja-dup-monito [ 3543] } hitcount: 2 767 { id: sys_read [ 0], common_pid: NetworkManager [ 890] } hitcount: 2 768 { id: sys_read [ 0], common_pid: evolution-calen [ 3048] } hitcount: 2 769 { id: sys_read [ 0], common_pid: postgres [ 1864] } hitcount: 2 770 { id: sys_read [ 0], common_pid: nm-applet [ 3022] } hitcount: 2 771 { id: sys_read [ 0], common_pid: whoopsie [ 1212] } hitcount: 2 772 . 773 . 774 . 775 { id: sys_ioctl [ 16], common_pid: bash [ 8479] } hitcount: 1 776 { id: sys_ioctl [ 16], common_pid: bash [ 3472] } hitcount: 12 777 { id: sys_ioctl [ 16], common_pid: gnome-terminal [ 3199] } hitcount: 16 778 { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 1808 779 { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 5580 780 . 781 . 782 . 783 { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2690] } hitcount: 3 784 { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2688] } hitcount: 16 785 { id: sys_inotify_add_watch [254], common_pid: gmain [ 975] } hitcount: 2 786 { id: sys_inotify_add_watch [254], common_pid: gmain [ 3204] } hitcount: 4 787 { id: sys_inotify_add_watch [254], common_pid: gmain [ 2888] } hitcount: 4 788 { id: sys_inotify_add_watch [254], common_pid: gmain [ 3003] } hitcount: 4 789 { id: sys_inotify_add_watch [254], common_pid: gmain [ 2873] } hitcount: 4 790 { id: sys_inotify_add_watch [254], common_pid: gmain [ 3196] } hitcount: 6 791 { id: sys_openat [257], common_pid: java [ 2623] } hitcount: 2 792 { id: sys_eventfd2 [290], common_pid: ibus-ui-gtk3 [ 2760] } hitcount: 4 793 { id: sys_eventfd2 [290], common_pid: compiz [ 2994] } hitcount: 6 794 795 Totals: 796 Hits: 31536 797 Entries: 323 798 Dropped: 0 799 800 The above list does give us a breakdown of the ioctl syscall by 801 pid, but it also gives us quite a bit more than that, which we 802 don't really care about at the moment. Since we know the syscall 803 id for sys_ioctl (16, displayed next to the sys_ioctl name), we 804 can use that to filter out all the other syscalls:: 805 806 # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \ 807 /sys/kernel/tracing/events/raw_syscalls/sys_enter/trigger 808 809 # cat /sys/kernel/tracing/events/raw_syscalls/sys_enter/hist 810 # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active] 811 812 { id: sys_ioctl [ 16], common_pid: gmain [ 2769] } hitcount: 1 813 { id: sys_ioctl [ 16], common_pid: evolution-addre [ 8571] } hitcount: 1 814 { id: sys_ioctl [ 16], common_pid: gmain [ 3003] } hitcount: 1 815 { id: sys_ioctl [ 16], common_pid: gmain [ 2781] } hitcount: 1 816 { id: sys_ioctl [ 16], common_pid: gmain [ 2829] } hitcount: 1 817 { id: sys_ioctl [ 16], common_pid: bash [ 8726] } hitcount: 1 818 { id: sys_ioctl [ 16], common_pid: bash [ 8508] } hitcount: 1 819 { id: sys_ioctl [ 16], common_pid: gmain [ 2970] } hitcount: 1 820 { id: sys_ioctl [ 16], common_pid: gmain [ 2768] } hitcount: 1 821 . 822 . 823 . 824 { id: sys_ioctl [ 16], common_pid: pool [ 8559] } hitcount: 45 825 { id: sys_ioctl [ 16], common_pid: pool [ 8555] } hitcount: 48 826 { id: sys_ioctl [ 16], common_pid: pool [ 8551] } hitcount: 48 827 { id: sys_ioctl [ 16], common_pid: avahi-daemon [ 896] } hitcount: 66 828 { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 26674 829 { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 73443 830 831 Totals: 832 Hits: 101162 833 Entries: 103 834 Dropped: 0 835 836 The above output shows that 'compiz' and 'Xorg' are far and away 837 the heaviest ioctl callers (which might lead to questions about 838 whether they really need to be making all those calls and to 839 possible avenues for further investigation.) 840 841 The compound key examples used a key and a sum value (hitcount) to 842 sort the output, but we can just as easily use two keys instead. 843 Here's an example where we use a compound key composed of the the 844 common_pid and size event fields. Sorting with pid as the primary 845 key and 'size' as the secondary key allows us to display an 846 ordered summary of the recvfrom sizes, with counts, received by 847 each process:: 848 849 # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \ 850 /sys/kernel/tracing/events/syscalls/sys_enter_recvfrom/trigger 851 852 # cat /sys/kernel/tracing/events/syscalls/sys_enter_recvfrom/hist 853 # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active] 854 855 { common_pid: smbd [ 784], size: 4 } hitcount: 1 856 { common_pid: dnsmasq [ 1412], size: 4096 } hitcount: 672 857 { common_pid: postgres [ 1796], size: 1000 } hitcount: 6 858 { common_pid: postgres [ 1867], size: 1000 } hitcount: 10 859 { common_pid: bamfdaemon [ 2787], size: 28 } hitcount: 2 860 { common_pid: bamfdaemon [ 2787], size: 14360 } hitcount: 1 861 { common_pid: compiz [ 2994], size: 8 } hitcount: 1 862 { common_pid: compiz [ 2994], size: 20 } hitcount: 11 863 { common_pid: gnome-terminal [ 3199], size: 4 } hitcount: 2 864 { common_pid: firefox [ 8817], size: 4 } hitcount: 1 865 { common_pid: firefox [ 8817], size: 8 } hitcount: 5 866 { common_pid: firefox [ 8817], size: 588 } hitcount: 2 867 { common_pid: firefox [ 8817], size: 628 } hitcount: 1 868 { common_pid: firefox [ 8817], size: 6944 } hitcount: 1 869 { common_pid: firefox [ 8817], size: 408880 } hitcount: 2 870 { common_pid: firefox [ 8822], size: 8 } hitcount: 2 871 { common_pid: firefox [ 8822], size: 160 } hitcount: 2 872 { common_pid: firefox [ 8822], size: 320 } hitcount: 2 873 { common_pid: firefox [ 8822], size: 352 } hitcount: 1 874 . 875 . 876 . 877 { common_pid: pool [ 8923], size: 1960 } hitcount: 10 878 { common_pid: pool [ 8923], size: 2048 } hitcount: 10 879 { common_pid: pool [ 8924], size: 1960 } hitcount: 10 880 { common_pid: pool [ 8924], size: 2048 } hitcount: 10 881 { common_pid: pool [ 8928], size: 1964 } hitcount: 4 882 { common_pid: pool [ 8928], size: 1965 } hitcount: 2 883 { common_pid: pool [ 8928], size: 2048 } hitcount: 6 884 { common_pid: pool [ 8929], size: 1982 } hitcount: 1 885 { common_pid: pool [ 8929], size: 2048 } hitcount: 1 886 887 Totals: 888 Hits: 2016 889 Entries: 224 890 Dropped: 0 891 892 The above example also illustrates the fact that although a compound 893 key is treated as a single entity for hashing purposes, the sub-keys 894 it's composed of can be accessed independently. 895 896 The next example uses a string field as the hash key and 897 demonstrates how you can manually pause and continue a hist trigger. 898 In this example, we'll aggregate fork counts and don't expect a 899 large number of entries in the hash table, so we'll drop it to a 900 much smaller number, say 256:: 901 902 # echo 'hist:key=child_comm:val=hitcount:size=256' > \ 903 /sys/kernel/tracing/events/sched/sched_process_fork/trigger 904 905 # cat /sys/kernel/tracing/events/sched/sched_process_fork/hist 906 # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active] 907 908 { child_comm: dconf worker } hitcount: 1 909 { child_comm: ibus-daemon } hitcount: 1 910 { child_comm: whoopsie } hitcount: 1 911 { child_comm: smbd } hitcount: 1 912 { child_comm: gdbus } hitcount: 1 913 { child_comm: kthreadd } hitcount: 1 914 { child_comm: dconf worker } hitcount: 1 915 { child_comm: evolution-alarm } hitcount: 2 916 { child_comm: Socket Thread } hitcount: 2 917 { child_comm: postgres } hitcount: 2 918 { child_comm: bash } hitcount: 3 919 { child_comm: compiz } hitcount: 3 920 { child_comm: evolution-sourc } hitcount: 4 921 { child_comm: dhclient } hitcount: 4 922 { child_comm: pool } hitcount: 5 923 { child_comm: nm-dispatcher.a } hitcount: 8 924 { child_comm: firefox } hitcount: 8 925 { child_comm: dbus-daemon } hitcount: 8 926 { child_comm: glib-pacrunner } hitcount: 10 927 { child_comm: evolution } hitcount: 23 928 929 Totals: 930 Hits: 89 931 Entries: 20 932 Dropped: 0 933 934 If we want to pause the hist trigger, we can simply append :pause to 935 the command that started the trigger. Notice that the trigger info 936 displays as [paused]:: 937 938 # echo 'hist:key=child_comm:val=hitcount:size=256:pause' >> \ 939 /sys/kernel/tracing/events/sched/sched_process_fork/trigger 940 941 # cat /sys/kernel/tracing/events/sched/sched_process_fork/hist 942 # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [paused] 943 944 { child_comm: dconf worker } hitcount: 1 945 { child_comm: kthreadd } hitcount: 1 946 { child_comm: dconf worker } hitcount: 1 947 { child_comm: gdbus } hitcount: 1 948 { child_comm: ibus-daemon } hitcount: 1 949 { child_comm: Socket Thread } hitcount: 2 950 { child_comm: evolution-alarm } hitcount: 2 951 { child_comm: smbd } hitcount: 2 952 { child_comm: bash } hitcount: 3 953 { child_comm: whoopsie } hitcount: 3 954 { child_comm: compiz } hitcount: 3 955 { child_comm: evolution-sourc } hitcount: 4 956 { child_comm: pool } hitcount: 5 957 { child_comm: postgres } hitcount: 6 958 { child_comm: firefox } hitcount: 8 959 { child_comm: dhclient } hitcount: 10 960 { child_comm: emacs } hitcount: 12 961 { child_comm: dbus-daemon } hitcount: 20 962 { child_comm: nm-dispatcher.a } hitcount: 20 963 { child_comm: evolution } hitcount: 35 964 { child_comm: glib-pacrunner } hitcount: 59 965 966 Totals: 967 Hits: 199 968 Entries: 21 969 Dropped: 0 970 971 To manually continue having the trigger aggregate events, append 972 :cont instead. Notice that the trigger info displays as [active] 973 again, and the data has changed:: 974 975 # echo 'hist:key=child_comm:val=hitcount:size=256:cont' >> \ 976 /sys/kernel/tracing/events/sched/sched_process_fork/trigger 977 978 # cat /sys/kernel/tracing/events/sched/sched_process_fork/hist 979 # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active] 980 981 { child_comm: dconf worker } hitcount: 1 982 { child_comm: dconf worker } hitcount: 1 983 { child_comm: kthreadd } hitcount: 1 984 { child_comm: gdbus } hitcount: 1 985 { child_comm: ibus-daemon } hitcount: 1 986 { child_comm: Socket Thread } hitcount: 2 987 { child_comm: evolution-alarm } hitcount: 2 988 { child_comm: smbd } hitcount: 2 989 { child_comm: whoopsie } hitcount: 3 990 { child_comm: compiz } hitcount: 3 991 { child_comm: evolution-sourc } hitcount: 4 992 { child_comm: bash } hitcount: 5 993 { child_comm: pool } hitcount: 5 994 { child_comm: postgres } hitcount: 6 995 { child_comm: firefox } hitcount: 8 996 { child_comm: dhclient } hitcount: 11 997 { child_comm: emacs } hitcount: 12 998 { child_comm: dbus-daemon } hitcount: 22 999 { child_comm: nm-dispatcher.a } hitcount: 22 1000 { child_comm: evolution } hitcount: 35 1001 { child_comm: glib-pacrunner } hitcount: 59 1002 1003 Totals: 1004 Hits: 206 1005 Entries: 21 1006 Dropped: 0 1007 1008 The previous example showed how to start and stop a hist trigger by 1009 appending 'pause' and 'continue' to the hist trigger command. A 1010 hist trigger can also be started in a paused state by initially 1011 starting the trigger with ':pause' appended. This allows you to 1012 start the trigger only when you're ready to start collecting data 1013 and not before. For example, you could start the trigger in a 1014 paused state, then unpause it and do something you want to measure, 1015 then pause the trigger again when done. 1016 1017 Of course, doing this manually can be difficult and error-prone, but 1018 it is possible to automatically start and stop a hist trigger based 1019 on some condition, via the enable_hist and disable_hist triggers. 1020 1021 For example, suppose we wanted to take a look at the relative 1022 weights in terms of skb length for each callpath that leads to a 1023 netif_receive_skb event when downloading a decent-sized file using 1024 wget. 1025 1026 First we set up an initially paused stacktrace trigger on the 1027 netif_receive_skb event:: 1028 1029 # echo 'hist:key=common_stacktrace:vals=len:pause' > \ 1030 /sys/kernel/tracing/events/net/netif_receive_skb/trigger 1031 1032 Next, we set up an 'enable_hist' trigger on the sched_process_exec 1033 event, with an 'if filename==/usr/bin/wget' filter. The effect of 1034 this new trigger is that it will 'unpause' the hist trigger we just 1035 set up on netif_receive_skb if and only if it sees a 1036 sched_process_exec event with a filename of '/usr/bin/wget'. When 1037 that happens, all netif_receive_skb events are aggregated into a 1038 hash table keyed on stacktrace:: 1039 1040 # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \ 1041 /sys/kernel/tracing/events/sched/sched_process_exec/trigger 1042 1043 The aggregation continues until the netif_receive_skb is paused 1044 again, which is what the following disable_hist event does by 1045 creating a similar setup on the sched_process_exit event, using the 1046 filter 'comm==wget':: 1047 1048 # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \ 1049 /sys/kernel/tracing/events/sched/sched_process_exit/trigger 1050 1051 Whenever a process exits and the comm field of the disable_hist 1052 trigger filter matches 'comm==wget', the netif_receive_skb hist 1053 trigger is disabled. 1054 1055 The overall effect is that netif_receive_skb events are aggregated 1056 into the hash table for only the duration of the wget. Executing a 1057 wget command and then listing the 'hist' file will display the 1058 output generated by the wget command:: 1059 1060 $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz 1061 1062 # cat /sys/kernel/tracing/events/net/netif_receive_skb/hist 1063 # trigger info: hist:keys=common_stacktrace:vals=len:sort=hitcount:size=2048 [paused] 1064 1065 { common_stacktrace: 1066 __netif_receive_skb_core+0x46d/0x990 1067 __netif_receive_skb+0x18/0x60 1068 netif_receive_skb_internal+0x23/0x90 1069 napi_gro_receive+0xc8/0x100 1070 ieee80211_deliver_skb+0xd6/0x270 [mac80211] 1071 ieee80211_rx_handlers+0xccf/0x22f0 [mac80211] 1072 ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211] 1073 ieee80211_rx+0x31d/0x900 [mac80211] 1074 iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm] 1075 iwl_rx_dispatch+0x8e/0xf0 [iwldvm] 1076 iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi] 1077 irq_thread_fn+0x20/0x50 1078 irq_thread+0x11f/0x150 1079 kthread+0xd2/0xf0 1080 ret_from_fork+0x42/0x70 1081 } hitcount: 85 len: 28884 1082 { common_stacktrace: 1083 __netif_receive_skb_core+0x46d/0x990 1084 __netif_receive_skb+0x18/0x60 1085 netif_receive_skb_internal+0x23/0x90 1086 napi_gro_complete+0xa4/0xe0 1087 dev_gro_receive+0x23a/0x360 1088 napi_gro_receive+0x30/0x100 1089 ieee80211_deliver_skb+0xd6/0x270 [mac80211] 1090 ieee80211_rx_handlers+0xccf/0x22f0 [mac80211] 1091 ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211] 1092 ieee80211_rx+0x31d/0x900 [mac80211] 1093 iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm] 1094 iwl_rx_dispatch+0x8e/0xf0 [iwldvm] 1095 iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi] 1096 irq_thread_fn+0x20/0x50 1097 irq_thread+0x11f/0x150 1098 kthread+0xd2/0xf0 1099 } hitcount: 98 len: 664329 1100 { common_stacktrace: 1101 __netif_receive_skb_core+0x46d/0x990 1102 __netif_receive_skb+0x18/0x60 1103 process_backlog+0xa8/0x150 1104 net_rx_action+0x15d/0x340 1105 __do_softirq+0x114/0x2c0 1106 do_softirq_own_stack+0x1c/0x30 1107 do_softirq+0x65/0x70 1108 __local_bh_enable_ip+0xb5/0xc0 1109 ip_finish_output+0x1f4/0x840 1110 ip_output+0x6b/0xc0 1111 ip_local_out_sk+0x31/0x40 1112 ip_send_skb+0x1a/0x50 1113 udp_send_skb+0x173/0x2a0 1114 udp_sendmsg+0x2bf/0x9f0 1115 inet_sendmsg+0x64/0xa0 1116 sock_sendmsg+0x3d/0x50 1117 } hitcount: 115 len: 13030 1118 { common_stacktrace: 1119 __netif_receive_skb_core+0x46d/0x990 1120 __netif_receive_skb+0x18/0x60 1121 netif_receive_skb_internal+0x23/0x90 1122 napi_gro_complete+0xa4/0xe0 1123 napi_gro_flush+0x6d/0x90 1124 iwl_pcie_irq_handler+0x92a/0x12f0 [iwlwifi] 1125 irq_thread_fn+0x20/0x50 1126 irq_thread+0x11f/0x150 1127 kthread+0xd2/0xf0 1128 ret_from_fork+0x42/0x70 1129 } hitcount: 934 len: 5512212 1130 1131 Totals: 1132 Hits: 1232 1133 Entries: 4 1134 Dropped: 0 1135 1136 The above shows all the netif_receive_skb callpaths and their total 1137 lengths for the duration of the wget command. 1138 1139 The 'clear' hist trigger param can be used to clear the hash table. 1140 Suppose we wanted to try another run of the previous example but 1141 this time also wanted to see the complete list of events that went 1142 into the histogram. In order to avoid having to set everything up 1143 again, we can just clear the histogram first:: 1144 1145 # echo 'hist:key=common_stacktrace:vals=len:clear' >> \ 1146 /sys/kernel/tracing/events/net/netif_receive_skb/trigger 1147 1148 Just to verify that it is in fact cleared, here's what we now see in 1149 the hist file:: 1150 1151 # cat /sys/kernel/tracing/events/net/netif_receive_skb/hist 1152 # trigger info: hist:keys=common_stacktrace:vals=len:sort=hitcount:size=2048 [paused] 1153 1154 Totals: 1155 Hits: 0 1156 Entries: 0 1157 Dropped: 0 1158 1159 Since we want to see the detailed list of every netif_receive_skb 1160 event occurring during the new run, which are in fact the same 1161 events being aggregated into the hash table, we add some additional 1162 'enable_event' events to the triggering sched_process_exec and 1163 sched_process_exit events as such:: 1164 1165 # echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \ 1166 /sys/kernel/tracing/events/sched/sched_process_exec/trigger 1167 1168 # echo 'disable_event:net:netif_receive_skb if comm==wget' > \ 1169 /sys/kernel/tracing/events/sched/sched_process_exit/trigger 1170 1171 If you read the trigger files for the sched_process_exec and 1172 sched_process_exit triggers, you should see two triggers for each: 1173 one enabling/disabling the hist aggregation and the other 1174 enabling/disabling the logging of events:: 1175 1176 # cat /sys/kernel/tracing/events/sched/sched_process_exec/trigger 1177 enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget 1178 enable_hist:net:netif_receive_skb:unlimited if filename==/usr/bin/wget 1179 1180 # cat /sys/kernel/tracing/events/sched/sched_process_exit/trigger 1181 enable_event:net:netif_receive_skb:unlimited if comm==wget 1182 disable_hist:net:netif_receive_skb:unlimited if comm==wget 1183 1184 In other words, whenever either of the sched_process_exec or 1185 sched_process_exit events is hit and matches 'wget', it enables or 1186 disables both the histogram and the event log, and what you end up 1187 with is a hash table and set of events just covering the specified 1188 duration. Run the wget command again:: 1189 1190 $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz 1191 1192 Displaying the 'hist' file should show something similar to what you 1193 saw in the last run, but this time you should also see the 1194 individual events in the trace file:: 1195 1196 # cat /sys/kernel/tracing/trace 1197 1198 # tracer: nop 1199 # 1200 # entries-in-buffer/entries-written: 183/1426 #P:4 1201 # 1202 # _-----=> irqs-off 1203 # / _----=> need-resched 1204 # | / _---=> hardirq/softirq 1205 # || / _--=> preempt-depth 1206 # ||| / delay 1207 # TASK-PID CPU# |||| TIMESTAMP FUNCTION 1208 # | | | |||| | | 1209 wget-15108 [000] ..s1 31769.606929: netif_receive_skb: dev=lo skbaddr=ffff88009c353100 len=60 1210 wget-15108 [000] ..s1 31769.606999: netif_receive_skb: dev=lo skbaddr=ffff88009c353200 len=60 1211 dnsmasq-1382 [000] ..s1 31769.677652: netif_receive_skb: dev=lo skbaddr=ffff88009c352b00 len=130 1212 dnsmasq-1382 [000] ..s1 31769.685917: netif_receive_skb: dev=lo skbaddr=ffff88009c352200 len=138 1213 ##### CPU 2 buffer started #### 1214 irq/29-iwlwifi-559 [002] ..s. 31772.031529: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433d00 len=2948 1215 irq/29-iwlwifi-559 [002] ..s. 31772.031572: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432200 len=1500 1216 irq/29-iwlwifi-559 [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948 1217 irq/29-iwlwifi-559 [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948 1218 irq/29-iwlwifi-559 [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500 1219 . 1220 . 1221 . 1222 1223 The following example demonstrates how multiple hist triggers can be 1224 attached to a given event. This capability can be useful for 1225 creating a set of different summaries derived from the same set of 1226 events, or for comparing the effects of different filters, among 1227 other things:: 1228 1229 # echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \ 1230 /sys/kernel/tracing/events/net/netif_receive_skb/trigger 1231 # echo 'hist:keys=skbaddr.hex:vals=len if len > 4096' >> \ 1232 /sys/kernel/tracing/events/net/netif_receive_skb/trigger 1233 # echo 'hist:keys=skbaddr.hex:vals=len if len == 256' >> \ 1234 /sys/kernel/tracing/events/net/netif_receive_skb/trigger 1235 # echo 'hist:keys=skbaddr.hex:vals=len' >> \ 1236 /sys/kernel/tracing/events/net/netif_receive_skb/trigger 1237 # echo 'hist:keys=len:vals=common_preempt_count' >> \ 1238 /sys/kernel/tracing/events/net/netif_receive_skb/trigger 1239 1240 The above set of commands create four triggers differing only in 1241 their filters, along with a completely different though fairly 1242 nonsensical trigger. Note that in order to append multiple hist 1243 triggers to the same file, you should use the '>>' operator to 1244 append them ('>' will also add the new hist trigger, but will remove 1245 any existing hist triggers beforehand). 1246 1247 Displaying the contents of the 'hist' file for the event shows the 1248 contents of all five histograms:: 1249 1250 # cat /sys/kernel/tracing/events/net/netif_receive_skb/hist 1251 1252 # event histogram 1253 # 1254 # trigger info: hist:keys=len:vals=hitcount,common_preempt_count:sort=hitcount:size=2048 [active] 1255 # 1256 1257 { len: 176 } hitcount: 1 common_preempt_count: 0 1258 { len: 223 } hitcount: 1 common_preempt_count: 0 1259 { len: 4854 } hitcount: 1 common_preempt_count: 0 1260 { len: 395 } hitcount: 1 common_preempt_count: 0 1261 { len: 177 } hitcount: 1 common_preempt_count: 0 1262 { len: 446 } hitcount: 1 common_preempt_count: 0 1263 { len: 1601 } hitcount: 1 common_preempt_count: 0 1264 . 1265 . 1266 . 1267 { len: 1280 } hitcount: 66 common_preempt_count: 0 1268 { len: 116 } hitcount: 81 common_preempt_count: 40 1269 { len: 708 } hitcount: 112 common_preempt_count: 0 1270 { len: 46 } hitcount: 221 common_preempt_count: 0 1271 { len: 1264 } hitcount: 458 common_preempt_count: 0 1272 1273 Totals: 1274 Hits: 1428 1275 Entries: 147 1276 Dropped: 0 1277 1278 1279 # event histogram 1280 # 1281 # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active] 1282 # 1283 1284 { skbaddr: ffff8800baee5e00 } hitcount: 1 len: 130 1285 { skbaddr: ffff88005f3d5600 } hitcount: 1 len: 1280 1286 { skbaddr: ffff88005f3d4900 } hitcount: 1 len: 1280 1287 { skbaddr: ffff88009fed6300 } hitcount: 1 len: 115 1288 { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 115 1289 { skbaddr: ffff88008cdb1900 } hitcount: 1 len: 46 1290 { skbaddr: ffff880064b5ef00 } hitcount: 1 len: 118 1291 { skbaddr: ffff880044e3c700 } hitcount: 1 len: 60 1292 { skbaddr: ffff880100065900 } hitcount: 1 len: 46 1293 { skbaddr: ffff8800d46bd500 } hitcount: 1 len: 116 1294 { skbaddr: ffff88005f3d5f00 } hitcount: 1 len: 1280 1295 { skbaddr: ffff880100064700 } hitcount: 1 len: 365 1296 { skbaddr: ffff8800badb6f00 } hitcount: 1 len: 60 1297 . 1298 . 1299 . 1300 { skbaddr: ffff88009fe0be00 } hitcount: 27 len: 24677 1301 { skbaddr: ffff88009fe0a400 } hitcount: 27 len: 23052 1302 { skbaddr: ffff88009fe0b700 } hitcount: 31 len: 25589 1303 { skbaddr: ffff88009fe0b600 } hitcount: 32 len: 27326 1304 { skbaddr: ffff88006a462800 } hitcount: 68 len: 71678 1305 { skbaddr: ffff88006a463700 } hitcount: 70 len: 72678 1306 { skbaddr: ffff88006a462b00 } hitcount: 71 len: 77589 1307 { skbaddr: ffff88006a463600 } hitcount: 73 len: 71307 1308 { skbaddr: ffff88006a462200 } hitcount: 81 len: 81032 1309 1310 Totals: 1311 Hits: 1451 1312 Entries: 318 1313 Dropped: 0 1314 1315 1316 # event histogram 1317 # 1318 # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len == 256 [active] 1319 # 1320 1321 1322 Totals: 1323 Hits: 0 1324 Entries: 0 1325 Dropped: 0 1326 1327 1328 # event histogram 1329 # 1330 # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len > 4096 [active] 1331 # 1332 1333 { skbaddr: ffff88009fd2c300 } hitcount: 1 len: 7212 1334 { skbaddr: ffff8800d2bcce00 } hitcount: 1 len: 7212 1335 { skbaddr: ffff8800d2bcd700 } hitcount: 1 len: 7212 1336 { skbaddr: ffff8800d2bcda00 } hitcount: 1 len: 21492 1337 { skbaddr: ffff8800ae2e2d00 } hitcount: 1 len: 7212 1338 { skbaddr: ffff8800d2bcdb00 } hitcount: 1 len: 7212 1339 { skbaddr: ffff88006a4df500 } hitcount: 1 len: 4854 1340 { skbaddr: ffff88008ce47b00 } hitcount: 1 len: 18636 1341 { skbaddr: ffff8800ae2e2200 } hitcount: 1 len: 12924 1342 { skbaddr: ffff88005f3e1000 } hitcount: 1 len: 4356 1343 { skbaddr: ffff8800d2bcdc00 } hitcount: 2 len: 24420 1344 { skbaddr: ffff8800d2bcc200 } hitcount: 2 len: 12996 1345 1346 Totals: 1347 Hits: 14 1348 Entries: 12 1349 Dropped: 0 1350 1351 1352 # event histogram 1353 # 1354 # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len < 0 [active] 1355 # 1356 1357 1358 Totals: 1359 Hits: 0 1360 Entries: 0 1361 Dropped: 0 1362 1363 Named triggers can be used to have triggers share a common set of 1364 histogram data. This capability is mostly useful for combining the 1365 output of events generated by tracepoints contained inside inline 1366 functions, but names can be used in a hist trigger on any event. 1367 For example, these two triggers when hit will update the same 'len' 1368 field in the shared 'foo' histogram data:: 1369 1370 # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \ 1371 /sys/kernel/tracing/events/net/netif_receive_skb/trigger 1372 # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \ 1373 /sys/kernel/tracing/events/net/netif_rx/trigger 1374 1375 You can see that they're updating common histogram data by reading 1376 each event's hist files at the same time:: 1377 1378 # cat /sys/kernel/tracing/events/net/netif_receive_skb/hist; 1379 cat /sys/kernel/tracing/events/net/netif_rx/hist 1380 1381 # event histogram 1382 # 1383 # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active] 1384 # 1385 1386 { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46 1387 { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76 1388 { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46 1389 { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468 1390 { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46 1391 { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52 1392 { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168 1393 { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46 1394 { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260 1395 { skbaddr: ffff880064505000 } hitcount: 1 len: 46 1396 { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32 1397 { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46 1398 { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44 1399 { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168 1400 { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40 1401 { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40 1402 { skbaddr: ffff880064505f00 } hitcount: 1 len: 174 1403 { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160 1404 { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76 1405 { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46 1406 { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32 1407 { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46 1408 { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988 1409 { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46 1410 { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44 1411 { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676 1412 { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107 1413 { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92 1414 { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142 1415 { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220 1416 { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92 1417 { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92 1418 { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675 1419 { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138 1420 { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138 1421 { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184 1422 { skbaddr: ffff880064504400 } hitcount: 4 len: 184 1423 { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184 1424 { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230 1425 { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196 1426 { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276 1427 { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276 1428 1429 Totals: 1430 Hits: 81 1431 Entries: 42 1432 Dropped: 0 1433 # event histogram 1434 # 1435 # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active] 1436 # 1437 1438 { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46 1439 { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76 1440 { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46 1441 { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468 1442 { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46 1443 { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52 1444 { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168 1445 { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46 1446 { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260 1447 { skbaddr: ffff880064505000 } hitcount: 1 len: 46 1448 { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32 1449 { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46 1450 { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44 1451 { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168 1452 { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40 1453 { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40 1454 { skbaddr: ffff880064505f00 } hitcount: 1 len: 174 1455 { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160 1456 { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76 1457 { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46 1458 { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32 1459 { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46 1460 { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988 1461 { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46 1462 { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44 1463 { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676 1464 { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107 1465 { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92 1466 { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142 1467 { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220 1468 { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92 1469 { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92 1470 { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675 1471 { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138 1472 { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138 1473 { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184 1474 { skbaddr: ffff880064504400 } hitcount: 4 len: 184 1475 { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184 1476 { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230 1477 { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196 1478 { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276 1479 { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276 1480 1481 Totals: 1482 Hits: 81 1483 Entries: 42 1484 Dropped: 0 1485 1486 And here's an example that shows how to combine histogram data from 1487 any two events even if they don't share any 'compatible' fields 1488 other than 'hitcount' and 'common_stacktrace'. These commands create a 1489 couple of triggers named 'bar' using those fields:: 1490 1491 # echo 'hist:name=bar:key=common_stacktrace:val=hitcount' > \ 1492 /sys/kernel/tracing/events/sched/sched_process_fork/trigger 1493 # echo 'hist:name=bar:key=common_stacktrace:val=hitcount' > \ 1494 /sys/kernel/tracing/events/net/netif_rx/trigger 1495 1496 And displaying the output of either shows some interesting if 1497 somewhat confusing output:: 1498 1499 # cat /sys/kernel/tracing/events/sched/sched_process_fork/hist 1500 # cat /sys/kernel/tracing/events/net/netif_rx/hist 1501 1502 # event histogram 1503 # 1504 # trigger info: hist:name=bar:keys=common_stacktrace:vals=hitcount:sort=hitcount:size=2048 [active] 1505 # 1506 1507 { common_stacktrace: 1508 kernel_clone+0x18e/0x330 1509 kernel_thread+0x29/0x30 1510 kthreadd+0x154/0x1b0 1511 ret_from_fork+0x3f/0x70 1512 } hitcount: 1 1513 { common_stacktrace: 1514 netif_rx_internal+0xb2/0xd0 1515 netif_rx_ni+0x20/0x70 1516 dev_loopback_xmit+0xaa/0xd0 1517 ip_mc_output+0x126/0x240 1518 ip_local_out_sk+0x31/0x40 1519 igmp_send_report+0x1e9/0x230 1520 igmp_timer_expire+0xe9/0x120 1521 call_timer_fn+0x39/0xf0 1522 run_timer_softirq+0x1e1/0x290 1523 __do_softirq+0xfd/0x290 1524 irq_exit+0x98/0xb0 1525 smp_apic_timer_interrupt+0x4a/0x60 1526 apic_timer_interrupt+0x6d/0x80 1527 cpuidle_enter+0x17/0x20 1528 call_cpuidle+0x3b/0x60 1529 cpu_startup_entry+0x22d/0x310 1530 } hitcount: 1 1531 { common_stacktrace: 1532 netif_rx_internal+0xb2/0xd0 1533 netif_rx_ni+0x20/0x70 1534 dev_loopback_xmit+0xaa/0xd0 1535 ip_mc_output+0x17f/0x240 1536 ip_local_out_sk+0x31/0x40 1537 ip_send_skb+0x1a/0x50 1538 udp_send_skb+0x13e/0x270 1539 udp_sendmsg+0x2bf/0x980 1540 inet_sendmsg+0x67/0xa0 1541 sock_sendmsg+0x38/0x50 1542 SYSC_sendto+0xef/0x170 1543 SyS_sendto+0xe/0x10 1544 entry_SYSCALL_64_fastpath+0x12/0x6a 1545 } hitcount: 2 1546 { common_stacktrace: 1547 netif_rx_internal+0xb2/0xd0 1548 netif_rx+0x1c/0x60 1549 loopback_xmit+0x6c/0xb0 1550 dev_hard_start_xmit+0x219/0x3a0 1551 __dev_queue_xmit+0x415/0x4f0 1552 dev_queue_xmit_sk+0x13/0x20 1553 ip_finish_output2+0x237/0x340 1554 ip_finish_output+0x113/0x1d0 1555 ip_output+0x66/0xc0 1556 ip_local_out_sk+0x31/0x40 1557 ip_send_skb+0x1a/0x50 1558 udp_send_skb+0x16d/0x270 1559 udp_sendmsg+0x2bf/0x980 1560 inet_sendmsg+0x67/0xa0 1561 sock_sendmsg+0x38/0x50 1562 ___sys_sendmsg+0x14e/0x270 1563 } hitcount: 76 1564 { common_stacktrace: 1565 netif_rx_internal+0xb2/0xd0 1566 netif_rx+0x1c/0x60 1567 loopback_xmit+0x6c/0xb0 1568 dev_hard_start_xmit+0x219/0x3a0 1569 __dev_queue_xmit+0x415/0x4f0 1570 dev_queue_xmit_sk+0x13/0x20 1571 ip_finish_output2+0x237/0x340 1572 ip_finish_output+0x113/0x1d0 1573 ip_output+0x66/0xc0 1574 ip_local_out_sk+0x31/0x40 1575 ip_send_skb+0x1a/0x50 1576 udp_send_skb+0x16d/0x270 1577 udp_sendmsg+0x2bf/0x980 1578 inet_sendmsg+0x67/0xa0 1579 sock_sendmsg+0x38/0x50 1580 ___sys_sendmsg+0x269/0x270 1581 } hitcount: 77 1582 { common_stacktrace: 1583 netif_rx_internal+0xb2/0xd0 1584 netif_rx+0x1c/0x60 1585 loopback_xmit+0x6c/0xb0 1586 dev_hard_start_xmit+0x219/0x3a0 1587 __dev_queue_xmit+0x415/0x4f0 1588 dev_queue_xmit_sk+0x13/0x20 1589 ip_finish_output2+0x237/0x340 1590 ip_finish_output+0x113/0x1d0 1591 ip_output+0x66/0xc0 1592 ip_local_out_sk+0x31/0x40 1593 ip_send_skb+0x1a/0x50 1594 udp_send_skb+0x16d/0x270 1595 udp_sendmsg+0x2bf/0x980 1596 inet_sendmsg+0x67/0xa0 1597 sock_sendmsg+0x38/0x50 1598 SYSC_sendto+0xef/0x170 1599 } hitcount: 88 1600 { common_stacktrace: 1601 kernel_clone+0x18e/0x330 1602 SyS_clone+0x19/0x20 1603 entry_SYSCALL_64_fastpath+0x12/0x6a 1604 } hitcount: 244 1605 1606 Totals: 1607 Hits: 489 1608 Entries: 7 1609 Dropped: 0 1610 16112.2 Inter-event hist triggers 1612----------------------------- 1613 1614Inter-event hist triggers are hist triggers that combine values from 1615one or more other events and create a histogram using that data. Data 1616from an inter-event histogram can in turn become the source for 1617further combined histograms, thus providing a chain of related 1618histograms, which is important for some applications. 1619 1620The most important example of an inter-event quantity that can be used 1621in this manner is latency, which is simply a difference in timestamps 1622between two events. Although latency is the most important 1623inter-event quantity, note that because the support is completely 1624general across the trace event subsystem, any event field can be used 1625in an inter-event quantity. 1626 1627An example of a histogram that combines data from other histograms 1628into a useful chain would be a 'wakeupswitch latency' histogram that 1629combines a 'wakeup latency' histogram and a 'switch latency' 1630histogram. 1631 1632Normally, a hist trigger specification consists of a (possibly 1633compound) key along with one or more numeric values, which are 1634continually updated sums associated with that key. A histogram 1635specification in this case consists of individual key and value 1636specifications that refer to trace event fields associated with a 1637single event type. 1638 1639The inter-event hist trigger extension allows fields from multiple 1640events to be referenced and combined into a multi-event histogram 1641specification. In support of this overall goal, a few enabling 1642features have been added to the hist trigger support: 1643 1644 - In order to compute an inter-event quantity, a value from one 1645 event needs to saved and then referenced from another event. This 1646 requires the introduction of support for histogram 'variables'. 1647 1648 - The computation of inter-event quantities and their combination 1649 require some minimal amount of support for applying simple 1650 expressions to variables (+ and -). 1651 1652 - A histogram consisting of inter-event quantities isn't logically a 1653 histogram on either event (so having the 'hist' file for either 1654 event host the histogram output doesn't really make sense). To 1655 address the idea that the histogram is associated with a 1656 combination of events, support is added allowing the creation of 1657 'synthetic' events that are events derived from other events. 1658 These synthetic events are full-fledged events just like any other 1659 and can be used as such, as for instance to create the 1660 'combination' histograms mentioned previously. 1661 1662 - A set of 'actions' can be associated with histogram entries - 1663 these can be used to generate the previously mentioned synthetic 1664 events, but can also be used for other purposes, such as for 1665 example saving context when a 'max' latency has been hit. 1666 1667 - Trace events don't have a 'timestamp' associated with them, but 1668 there is an implicit timestamp saved along with an event in the 1669 underlying ftrace ring buffer. This timestamp is now exposed as a 1670 a synthetic field named 'common_timestamp' which can be used in 1671 histograms as if it were any other event field; it isn't an actual 1672 field in the trace format but rather is a synthesized value that 1673 nonetheless can be used as if it were an actual field. By default 1674 it is in units of nanoseconds; appending '.usecs' to a 1675 common_timestamp field changes the units to microseconds. 1676 1677A note on inter-event timestamps: If common_timestamp is used in a 1678histogram, the trace buffer is automatically switched over to using 1679absolute timestamps and the "global" trace clock, in order to avoid 1680bogus timestamp differences with other clocks that aren't coherent 1681across CPUs. This can be overridden by specifying one of the other 1682trace clocks instead, using the "clock=XXX" hist trigger attribute, 1683where XXX is any of the clocks listed in the tracing/trace_clock 1684pseudo-file. 1685 1686These features are described in more detail in the following sections. 1687 16882.2.1 Histogram Variables 1689------------------------- 1690 1691Variables are simply named locations used for saving and retrieving 1692values between matching events. A 'matching' event is defined as an 1693event that has a matching key - if a variable is saved for a histogram 1694entry corresponding to that key, any subsequent event with a matching 1695key can access that variable. 1696 1697A variable's value is normally available to any subsequent event until 1698it is set to something else by a subsequent event. The one exception 1699to that rule is that any variable used in an expression is essentially 1700'read-once' - once it's used by an expression in a subsequent event, 1701it's reset to its 'unset' state, which means it can't be used again 1702unless it's set again. This ensures not only that an event doesn't 1703use an uninitialized variable in a calculation, but that that variable 1704is used only once and not for any unrelated subsequent match. 1705 1706The basic syntax for saving a variable is to simply prefix a unique 1707variable name not corresponding to any keyword along with an '=' sign 1708to any event field. 1709 1710Either keys or values can be saved and retrieved in this way. This 1711creates a variable named 'ts0' for a histogram entry with the key 1712'next_pid':: 1713 1714 # echo 'hist:keys=next_pid:vals=$ts0:ts0=common_timestamp ... >> \ 1715 event/trigger 1716 1717The ts0 variable can be accessed by any subsequent event having the 1718same pid as 'next_pid'. 1719 1720Variable references are formed by prepending the variable name with 1721the '$' sign. Thus for example, the ts0 variable above would be 1722referenced as '$ts0' in expressions. 1723 1724Because 'vals=' is used, the common_timestamp variable value above 1725will also be summed as a normal histogram value would (though for a 1726timestamp it makes little sense). 1727 1728The below shows that a key value can also be saved in the same way:: 1729 1730 # echo 'hist:timer_pid=common_pid:key=timer_pid ...' >> event/trigger 1731 1732If a variable isn't a key variable or prefixed with 'vals=', the 1733associated event field will be saved in a variable but won't be summed 1734as a value:: 1735 1736 # echo 'hist:keys=next_pid:ts1=common_timestamp ...' >> event/trigger 1737 1738Multiple variables can be assigned at the same time. The below would 1739result in both ts0 and b being created as variables, with both 1740common_timestamp and field1 additionally being summed as values:: 1741 1742 # echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ...' >> \ 1743 event/trigger 1744 1745Note that variable assignments can appear either preceding or 1746following their use. The command below behaves identically to the 1747command above:: 1748 1749 # echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ...' >> \ 1750 event/trigger 1751 1752Any number of variables not bound to a 'vals=' prefix can also be 1753assigned by simply separating them with colons. Below is the same 1754thing but without the values being summed in the histogram:: 1755 1756 # echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ...' >> event/trigger 1757 1758Variables set as above can be referenced and used in expressions on 1759another event. 1760 1761For example, here's how a latency can be calculated:: 1762 1763 # echo 'hist:keys=pid,prio:ts0=common_timestamp ...' >> event1/trigger 1764 # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ...' >> event2/trigger 1765 1766In the first line above, the event's timestamp is saved into the 1767variable ts0. In the next line, ts0 is subtracted from the second 1768event's timestamp to produce the latency, which is then assigned into 1769yet another variable, 'wakeup_lat'. The hist trigger below in turn 1770makes use of the wakeup_lat variable to compute a combined latency 1771using the same key and variable from yet another event:: 1772 1773 # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ...' >> event3/trigger 1774 1775Expressions support the use of addition, subtraction, multiplication and 1776division operators (+-\*/). 1777 1778Note if division by zero cannot be detected at parse time (i.e. the 1779divisor is not a constant), the result will be -1. 1780 1781Numeric constants can also be used directly in an expression:: 1782 1783 # echo 'hist:keys=next_pid:timestamp_secs=common_timestamp/1000000 ...' >> event/trigger 1784 1785or assigned to a variable and referenced in a subsequent expression:: 1786 1787 # echo 'hist:keys=next_pid:us_per_sec=1000000 ...' >> event/trigger 1788 # echo 'hist:keys=next_pid:timestamp_secs=common_timestamp/$us_per_sec ...' >> event/trigger 1789 1790Variables can even hold stacktraces, which are useful with synthetic events. 1791 17922.2.2 Synthetic Events 1793---------------------- 1794 1795Synthetic events are user-defined events generated from hist trigger 1796variables or fields associated with one or more other events. Their 1797purpose is to provide a mechanism for displaying data spanning 1798multiple events consistent with the existing and already familiar 1799usage for normal events. 1800 1801To define a synthetic event, the user writes a simple specification 1802consisting of the name of the new event along with one or more 1803variables and their types, which can be any valid field type, 1804separated by semicolons, to the tracing/synthetic_events file. 1805 1806See synth_field_size() for available types. 1807 1808If field_name contains [n], the field is considered to be a static array. 1809 1810If field_names contains[] (no subscript), the field is considered to 1811be a dynamic array, which will only take as much space in the event as 1812is required to hold the array. 1813 1814A string field can be specified using either the static notation: 1815 1816 char name[32]; 1817 1818Or the dynamic: 1819 1820 char name[]; 1821 1822The size limit for either is 256. 1823 1824For instance, the following creates a new event named 'wakeup_latency' 1825with 3 fields: lat, pid, and prio. Each of those fields is simply a 1826variable reference to a variable on another event:: 1827 1828 # echo 'wakeup_latency \ 1829 u64 lat; \ 1830 pid_t pid; \ 1831 int prio' >> \ 1832 /sys/kernel/tracing/synthetic_events 1833 1834Reading the tracing/synthetic_events file lists all the currently 1835defined synthetic events, in this case the event defined above:: 1836 1837 # cat /sys/kernel/tracing/synthetic_events 1838 wakeup_latency u64 lat; pid_t pid; int prio 1839 1840An existing synthetic event definition can be removed by prepending 1841the command that defined it with a '!':: 1842 1843 # echo '!wakeup_latency u64 lat pid_t pid int prio' >> \ 1844 /sys/kernel/tracing/synthetic_events 1845 1846At this point, there isn't yet an actual 'wakeup_latency' event 1847instantiated in the event subsystem - for this to happen, a 'hist 1848trigger action' needs to be instantiated and bound to actual fields 1849and variables defined on other events (see Section 2.2.3 below on 1850how that is done using hist trigger 'onmatch' action). Once that is 1851done, the 'wakeup_latency' synthetic event instance is created. 1852 1853The new event is created under the tracing/events/synthetic/ directory 1854and looks and behaves just like any other event:: 1855 1856 # ls /sys/kernel/tracing/events/synthetic/wakeup_latency 1857 enable filter format hist id trigger 1858 1859A histogram can now be defined for the new synthetic event:: 1860 1861 # echo 'hist:keys=pid,prio,lat.log2:sort=lat' >> \ 1862 /sys/kernel/tracing/events/synthetic/wakeup_latency/trigger 1863 1864The above shows the latency "lat" in a power of 2 grouping. 1865 1866Like any other event, once a histogram is enabled for the event, the 1867output can be displayed by reading the event's 'hist' file:: 1868 1869 # cat /sys/kernel/tracing/events/synthetic/wakeup_latency/hist 1870 1871 # event histogram 1872 # 1873 # trigger info: hist:keys=pid,prio,lat.log2:vals=hitcount:sort=lat.log2:size=2048 [active] 1874 # 1875 1876 { pid: 2035, prio: 9, lat: ~ 2^2 } hitcount: 43 1877 { pid: 2034, prio: 9, lat: ~ 2^2 } hitcount: 60 1878 { pid: 2029, prio: 9, lat: ~ 2^2 } hitcount: 965 1879 { pid: 2034, prio: 120, lat: ~ 2^2 } hitcount: 9 1880 { pid: 2033, prio: 120, lat: ~ 2^2 } hitcount: 5 1881 { pid: 2030, prio: 9, lat: ~ 2^2 } hitcount: 335 1882 { pid: 2030, prio: 120, lat: ~ 2^2 } hitcount: 10 1883 { pid: 2032, prio: 120, lat: ~ 2^2 } hitcount: 1 1884 { pid: 2035, prio: 120, lat: ~ 2^2 } hitcount: 2 1885 { pid: 2031, prio: 9, lat: ~ 2^2 } hitcount: 176 1886 { pid: 2028, prio: 120, lat: ~ 2^2 } hitcount: 15 1887 { pid: 2033, prio: 9, lat: ~ 2^2 } hitcount: 91 1888 { pid: 2032, prio: 9, lat: ~ 2^2 } hitcount: 125 1889 { pid: 2029, prio: 120, lat: ~ 2^2 } hitcount: 4 1890 { pid: 2031, prio: 120, lat: ~ 2^2 } hitcount: 3 1891 { pid: 2029, prio: 120, lat: ~ 2^3 } hitcount: 2 1892 { pid: 2035, prio: 9, lat: ~ 2^3 } hitcount: 41 1893 { pid: 2030, prio: 120, lat: ~ 2^3 } hitcount: 1 1894 { pid: 2032, prio: 9, lat: ~ 2^3 } hitcount: 32 1895 { pid: 2031, prio: 9, lat: ~ 2^3 } hitcount: 44 1896 { pid: 2034, prio: 9, lat: ~ 2^3 } hitcount: 40 1897 { pid: 2030, prio: 9, lat: ~ 2^3 } hitcount: 29 1898 { pid: 2033, prio: 9, lat: ~ 2^3 } hitcount: 31 1899 { pid: 2029, prio: 9, lat: ~ 2^3 } hitcount: 31 1900 { pid: 2028, prio: 120, lat: ~ 2^3 } hitcount: 18 1901 { pid: 2031, prio: 120, lat: ~ 2^3 } hitcount: 2 1902 { pid: 2028, prio: 120, lat: ~ 2^4 } hitcount: 1 1903 { pid: 2029, prio: 9, lat: ~ 2^4 } hitcount: 4 1904 { pid: 2031, prio: 120, lat: ~ 2^7 } hitcount: 1 1905 { pid: 2032, prio: 120, lat: ~ 2^7 } hitcount: 1 1906 1907 Totals: 1908 Hits: 2122 1909 Entries: 30 1910 Dropped: 0 1911 1912 1913The latency values can also be grouped linearly by a given size with 1914the ".buckets" modifier and specify a size (in this case groups of 10):: 1915 1916 # echo 'hist:keys=pid,prio,lat.buckets=10:sort=lat' >> \ 1917 /sys/kernel/tracing/events/synthetic/wakeup_latency/trigger 1918 1919 # event histogram 1920 # 1921 # trigger info: hist:keys=pid,prio,lat.buckets=10:vals=hitcount:sort=lat.buckets=10:size=2048 [active] 1922 # 1923 1924 { pid: 2067, prio: 9, lat: ~ 0-9 } hitcount: 220 1925 { pid: 2068, prio: 9, lat: ~ 0-9 } hitcount: 157 1926 { pid: 2070, prio: 9, lat: ~ 0-9 } hitcount: 100 1927 { pid: 2067, prio: 120, lat: ~ 0-9 } hitcount: 6 1928 { pid: 2065, prio: 120, lat: ~ 0-9 } hitcount: 2 1929 { pid: 2066, prio: 120, lat: ~ 0-9 } hitcount: 2 1930 { pid: 2069, prio: 9, lat: ~ 0-9 } hitcount: 122 1931 { pid: 2069, prio: 120, lat: ~ 0-9 } hitcount: 8 1932 { pid: 2070, prio: 120, lat: ~ 0-9 } hitcount: 1 1933 { pid: 2068, prio: 120, lat: ~ 0-9 } hitcount: 7 1934 { pid: 2066, prio: 9, lat: ~ 0-9 } hitcount: 365 1935 { pid: 2064, prio: 120, lat: ~ 0-9 } hitcount: 35 1936 { pid: 2065, prio: 9, lat: ~ 0-9 } hitcount: 998 1937 { pid: 2071, prio: 9, lat: ~ 0-9 } hitcount: 85 1938 { pid: 2065, prio: 9, lat: ~ 10-19 } hitcount: 2 1939 { pid: 2064, prio: 120, lat: ~ 10-19 } hitcount: 2 1940 1941 Totals: 1942 Hits: 2112 1943 Entries: 16 1944 Dropped: 0 1945 1946To save stacktraces, create a synthetic event with a field of type "unsigned long[]" 1947or even just "long[]". For example, to see how long a task is blocked in an 1948uninterruptible state:: 1949 1950 # cd /sys/kernel/tracing 1951 # echo 's:block_lat pid_t pid; u64 delta; unsigned long[] stack;' > dynamic_events 1952 # echo 'hist:keys=next_pid:ts=common_timestamp.usecs,st=common_stacktrace if prev_state == 2' >> events/sched/sched_switch/trigger 1953 # echo 'hist:keys=prev_pid:delta=common_timestamp.usecs-$ts,s=$st:onmax($delta).trace(block_lat,prev_pid,$delta,$s)' >> events/sched/sched_switch/trigger 1954 # echo 1 > events/synthetic/block_lat/enable 1955 # cat trace 1956 1957 # tracer: nop 1958 # 1959 # entries-in-buffer/entries-written: 2/2 #P:8 1960 # 1961 # _-----=> irqs-off/BH-disabled 1962 # / _----=> need-resched 1963 # | / _---=> hardirq/softirq 1964 # || / _--=> preempt-depth 1965 # ||| / _-=> migrate-disable 1966 # |||| / delay 1967 # TASK-PID CPU# ||||| TIMESTAMP FUNCTION 1968 # | | | ||||| | | 1969 <idle>-0 [005] d..4. 521.164922: block_lat: pid=0 delta=8322 stack=STACK: 1970 => __schedule+0x448/0x7b0 1971 => schedule+0x5a/0xb0 1972 => io_schedule+0x42/0x70 1973 => bit_wait_io+0xd/0x60 1974 => __wait_on_bit+0x4b/0x140 1975 => out_of_line_wait_on_bit+0x91/0xb0 1976 => jbd2_journal_commit_transaction+0x1679/0x1a70 1977 => kjournald2+0xa9/0x280 1978 => kthread+0xe9/0x110 1979 => ret_from_fork+0x2c/0x50 1980 1981 <...>-2 [004] d..4. 525.184257: block_lat: pid=2 delta=76 stack=STACK: 1982 => __schedule+0x448/0x7b0 1983 => schedule+0x5a/0xb0 1984 => schedule_timeout+0x11a/0x150 1985 => wait_for_completion_killable+0x144/0x1f0 1986 => __kthread_create_on_node+0xe7/0x1e0 1987 => kthread_create_on_node+0x51/0x70 1988 => create_worker+0xcc/0x1a0 1989 => worker_thread+0x2ad/0x380 1990 => kthread+0xe9/0x110 1991 => ret_from_fork+0x2c/0x50 1992 1993A synthetic event that has a stacktrace field may use it as a key in 1994histogram:: 1995 1996 # echo 'hist:keys=delta.buckets=100,stack.stacktrace:sort=delta' > events/synthetic/block_lat/trigger 1997 # cat events/synthetic/block_lat/hist 1998 1999 # event histogram 2000 # 2001 # trigger info: hist:keys=delta.buckets=100,stack.stacktrace:vals=hitcount:sort=delta.buckets=100:size=2048 [active] 2002 # 2003 { delta: ~ 0-99, stack.stacktrace __schedule+0xa19/0x1520 2004 schedule+0x6b/0x110 2005 io_schedule+0x46/0x80 2006 bit_wait_io+0x11/0x80 2007 __wait_on_bit+0x4e/0x120 2008 out_of_line_wait_on_bit+0x8d/0xb0 2009 __wait_on_buffer+0x33/0x40 2010 jbd2_journal_commit_transaction+0x155a/0x19b0 2011 kjournald2+0xab/0x270 2012 kthread+0xfa/0x130 2013 ret_from_fork+0x29/0x50 2014 } hitcount: 1 2015 { delta: ~ 0-99, stack.stacktrace __schedule+0xa19/0x1520 2016 schedule+0x6b/0x110 2017 io_schedule+0x46/0x80 2018 rq_qos_wait+0xd0/0x170 2019 wbt_wait+0x9e/0xf0 2020 __rq_qos_throttle+0x25/0x40 2021 blk_mq_submit_bio+0x2c3/0x5b0 2022 __submit_bio+0xff/0x190 2023 submit_bio_noacct_nocheck+0x25b/0x2b0 2024 submit_bio_noacct+0x20b/0x600 2025 submit_bio+0x28/0x90 2026 ext4_bio_write_page+0x1e0/0x8c0 2027 mpage_submit_page+0x60/0x80 2028 mpage_process_page_bufs+0x16c/0x180 2029 mpage_prepare_extent_to_map+0x23f/0x530 2030 } hitcount: 1 2031 { delta: ~ 0-99, stack.stacktrace __schedule+0xa19/0x1520 2032 schedule+0x6b/0x110 2033 schedule_hrtimeout_range_clock+0x97/0x110 2034 schedule_hrtimeout_range+0x13/0x20 2035 usleep_range_state+0x65/0x90 2036 __intel_wait_for_register+0x1c1/0x230 [i915] 2037 intel_psr_wait_for_idle_locked+0x171/0x2a0 [i915] 2038 intel_pipe_update_start+0x169/0x360 [i915] 2039 intel_update_crtc+0x112/0x490 [i915] 2040 skl_commit_modeset_enables+0x199/0x600 [i915] 2041 intel_atomic_commit_tail+0x7c4/0x1080 [i915] 2042 intel_atomic_commit_work+0x12/0x20 [i915] 2043 process_one_work+0x21c/0x3f0 2044 worker_thread+0x50/0x3e0 2045 kthread+0xfa/0x130 2046 } hitcount: 3 2047 { delta: ~ 0-99, stack.stacktrace __schedule+0xa19/0x1520 2048 schedule+0x6b/0x110 2049 schedule_timeout+0x11e/0x160 2050 __wait_for_common+0x8f/0x190 2051 wait_for_completion+0x24/0x30 2052 __flush_work.isra.0+0x1cc/0x360 2053 flush_work+0xe/0x20 2054 drm_mode_rmfb+0x18b/0x1d0 [drm] 2055 drm_mode_rmfb_ioctl+0x10/0x20 [drm] 2056 drm_ioctl_kernel+0xb8/0x150 [drm] 2057 drm_ioctl+0x243/0x560 [drm] 2058 __x64_sys_ioctl+0x92/0xd0 2059 do_syscall_64+0x59/0x90 2060 entry_SYSCALL_64_after_hwframe+0x72/0xdc 2061 } hitcount: 1 2062 { delta: ~ 0-99, stack.stacktrace __schedule+0xa19/0x1520 2063 schedule+0x6b/0x110 2064 schedule_timeout+0x87/0x160 2065 __wait_for_common+0x8f/0x190 2066 wait_for_completion_timeout+0x1d/0x30 2067 drm_atomic_helper_wait_for_flip_done+0x57/0x90 [drm_kms_helper] 2068 intel_atomic_commit_tail+0x8ce/0x1080 [i915] 2069 intel_atomic_commit_work+0x12/0x20 [i915] 2070 process_one_work+0x21c/0x3f0 2071 worker_thread+0x50/0x3e0 2072 kthread+0xfa/0x130 2073 ret_from_fork+0x29/0x50 2074 } hitcount: 1 2075 { delta: ~ 100-199, stack.stacktrace __schedule+0xa19/0x1520 2076 schedule+0x6b/0x110 2077 schedule_hrtimeout_range_clock+0x97/0x110 2078 schedule_hrtimeout_range+0x13/0x20 2079 usleep_range_state+0x65/0x90 2080 pci_set_low_power_state+0x17f/0x1f0 2081 pci_set_power_state+0x49/0x250 2082 pci_finish_runtime_suspend+0x4a/0x90 2083 pci_pm_runtime_suspend+0xcb/0x1b0 2084 __rpm_callback+0x48/0x120 2085 rpm_callback+0x67/0x70 2086 rpm_suspend+0x167/0x780 2087 rpm_idle+0x25a/0x380 2088 pm_runtime_work+0x93/0xc0 2089 process_one_work+0x21c/0x3f0 2090 } hitcount: 1 2091 2092 Totals: 2093 Hits: 10 2094 Entries: 7 2095 Dropped: 0 2096 20972.2.3 Hist trigger 'handlers' and 'actions' 2098------------------------------------------- 2099 2100A hist trigger 'action' is a function that's executed (in most cases 2101conditionally) whenever a histogram entry is added or updated. 2102 2103When a histogram entry is added or updated, a hist trigger 'handler' 2104is what decides whether the corresponding action is actually invoked 2105or not. 2106 2107Hist trigger handlers and actions are paired together in the general 2108form: 2109 2110 <handler>.<action> 2111 2112To specify a handler.action pair for a given event, simply specify 2113that handler.action pair between colons in the hist trigger 2114specification. 2115 2116In theory, any handler can be combined with any action, but in 2117practice, not every handler.action combination is currently supported; 2118if a given handler.action combination isn't supported, the hist 2119trigger will fail with -EINVAL; 2120 2121The default 'handler.action' if none is explicitly specified is as it 2122always has been, to simply update the set of values associated with an 2123entry. Some applications, however, may want to perform additional 2124actions at that point, such as generate another event, or compare and 2125save a maximum. 2126 2127The supported handlers and actions are listed below, and each is 2128described in more detail in the following paragraphs, in the context 2129of descriptions of some common and useful handler.action combinations. 2130 2131The available handlers are: 2132 2133 - onmatch(matching.event) - invoke action on any addition or update 2134 - onmax(var) - invoke action if var exceeds current max 2135 - onchange(var) - invoke action if var changes 2136 2137The available actions are: 2138 2139 - trace(<synthetic_event_name>,param list) - generate synthetic event 2140 - save(field,...) - save current event fields 2141 - snapshot() - snapshot the trace buffer 2142 2143The following commonly-used handler.action pairs are available: 2144 2145 - onmatch(matching.event).trace(<synthetic_event_name>,param list) 2146 2147 The 'onmatch(matching.event).trace(<synthetic_event_name>,param 2148 list)' hist trigger action is invoked whenever an event matches 2149 and the histogram entry would be added or updated. It causes the 2150 named synthetic event to be generated with the values given in the 2151 'param list'. The result is the generation of a synthetic event 2152 that consists of the values contained in those variables at the 2153 time the invoking event was hit. For example, if the synthetic 2154 event name is 'wakeup_latency', a wakeup_latency event is 2155 generated using onmatch(event).trace(wakeup_latency,arg1,arg2). 2156 2157 There is also an equivalent alternative form available for 2158 generating synthetic events. In this form, the synthetic event 2159 name is used as if it were a function name. For example, using 2160 the 'wakeup_latency' synthetic event name again, the 2161 wakeup_latency event would be generated by invoking it as if it 2162 were a function call, with the event field values passed in as 2163 arguments: onmatch(event).wakeup_latency(arg1,arg2). The syntax 2164 for this form is: 2165 2166 onmatch(matching.event).<synthetic_event_name>(param list) 2167 2168 In either case, the 'param list' consists of one or more 2169 parameters which may be either variables or fields defined on 2170 either the 'matching.event' or the target event. The variables or 2171 fields specified in the param list may be either fully-qualified 2172 or unqualified. If a variable is specified as unqualified, it 2173 must be unique between the two events. A field name used as a 2174 param can be unqualified if it refers to the target event, but 2175 must be fully qualified if it refers to the matching event. A 2176 fully-qualified name is of the form 'system.event_name.$var_name' 2177 or 'system.event_name.field'. 2178 2179 The 'matching.event' specification is simply the fully qualified 2180 event name of the event that matches the target event for the 2181 onmatch() functionality, in the form 'system.event_name'. Histogram 2182 keys of both events are compared to find if events match. In case 2183 multiple histogram keys are used, they all must match in the specified 2184 order. 2185 2186 Finally, the number and type of variables/fields in the 'param 2187 list' must match the number and types of the fields in the 2188 synthetic event being generated. 2189 2190 As an example the below defines a simple synthetic event and uses 2191 a variable defined on the sched_wakeup_new event as a parameter 2192 when invoking the synthetic event. Here we define the synthetic 2193 event:: 2194 2195 # echo 'wakeup_new_test pid_t pid' >> \ 2196 /sys/kernel/tracing/synthetic_events 2197 2198 # cat /sys/kernel/tracing/synthetic_events 2199 wakeup_new_test pid_t pid 2200 2201 The following hist trigger both defines the missing testpid 2202 variable and specifies an onmatch() action that generates a 2203 wakeup_new_test synthetic event whenever a sched_wakeup_new event 2204 occurs, which because of the 'if comm == "cyclictest"' filter only 2205 happens when the executable is cyclictest:: 2206 2207 # echo 'hist:keys=$testpid:testpid=pid:onmatch(sched.sched_wakeup_new).\ 2208 wakeup_new_test($testpid) if comm=="cyclictest"' >> \ 2209 /sys/kernel/tracing/events/sched/sched_wakeup_new/trigger 2210 2211 Or, equivalently, using the 'trace' keyword syntax:: 2212 2213 # echo 'hist:keys=$testpid:testpid=pid:onmatch(sched.sched_wakeup_new).\ 2214 trace(wakeup_new_test,$testpid) if comm=="cyclictest"' >> \ 2215 /sys/kernel/tracing/events/sched/sched_wakeup_new/trigger 2216 2217 Creating and displaying a histogram based on those events is now 2218 just a matter of using the fields and new synthetic event in the 2219 tracing/events/synthetic directory, as usual:: 2220 2221 # echo 'hist:keys=pid:sort=pid' >> \ 2222 /sys/kernel/tracing/events/synthetic/wakeup_new_test/trigger 2223 2224 Running 'cyclictest' should cause wakeup_new events to generate 2225 wakeup_new_test synthetic events which should result in histogram 2226 output in the wakeup_new_test event's hist file:: 2227 2228 # cat /sys/kernel/tracing/events/synthetic/wakeup_new_test/hist 2229 2230 A more typical usage would be to use two events to calculate a 2231 latency. The following example uses a set of hist triggers to 2232 produce a 'wakeup_latency' histogram. 2233 2234 First, we define a 'wakeup_latency' synthetic event:: 2235 2236 # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \ 2237 /sys/kernel/tracing/synthetic_events 2238 2239 Next, we specify that whenever we see a sched_waking event for a 2240 cyclictest thread, save the timestamp in a 'ts0' variable:: 2241 2242 # echo 'hist:keys=$saved_pid:saved_pid=pid:ts0=common_timestamp.usecs \ 2243 if comm=="cyclictest"' >> \ 2244 /sys/kernel/tracing/events/sched/sched_waking/trigger 2245 2246 Then, when the corresponding thread is actually scheduled onto the 2247 CPU by a sched_switch event (saved_pid matches next_pid), calculate 2248 the latency and use that along with another variable and an event field 2249 to generate a wakeup_latency synthetic event:: 2250 2251 # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0:\ 2252 onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,\ 2253 $saved_pid,next_prio) if next_comm=="cyclictest"' >> \ 2254 /sys/kernel/tracing/events/sched/sched_switch/trigger 2255 2256 We also need to create a histogram on the wakeup_latency synthetic 2257 event in order to aggregate the generated synthetic event data:: 2258 2259 # echo 'hist:keys=pid,prio,lat:sort=pid,lat' >> \ 2260 /sys/kernel/tracing/events/synthetic/wakeup_latency/trigger 2261 2262 Finally, once we've run cyclictest to actually generate some 2263 events, we can see the output by looking at the wakeup_latency 2264 synthetic event's hist file:: 2265 2266 # cat /sys/kernel/tracing/events/synthetic/wakeup_latency/hist 2267 2268 - onmax(var).save(field,.. .) 2269 2270 The 'onmax(var).save(field,...)' hist trigger action is invoked 2271 whenever the value of 'var' associated with a histogram entry 2272 exceeds the current maximum contained in that variable. 2273 2274 The end result is that the trace event fields specified as the 2275 onmax.save() params will be saved if 'var' exceeds the current 2276 maximum for that hist trigger entry. This allows context from the 2277 event that exhibited the new maximum to be saved for later 2278 reference. When the histogram is displayed, additional fields 2279 displaying the saved values will be printed. 2280 2281 As an example the below defines a couple of hist triggers, one for 2282 sched_waking and another for sched_switch, keyed on pid. Whenever 2283 a sched_waking occurs, the timestamp is saved in the entry 2284 corresponding to the current pid, and when the scheduler switches 2285 back to that pid, the timestamp difference is calculated. If the 2286 resulting latency, stored in wakeup_lat, exceeds the current 2287 maximum latency, the values specified in the save() fields are 2288 recorded:: 2289 2290 # echo 'hist:keys=pid:ts0=common_timestamp.usecs \ 2291 if comm=="cyclictest"' >> \ 2292 /sys/kernel/tracing/events/sched/sched_waking/trigger 2293 2294 # echo 'hist:keys=next_pid:\ 2295 wakeup_lat=common_timestamp.usecs-$ts0:\ 2296 onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) \ 2297 if next_comm=="cyclictest"' >> \ 2298 /sys/kernel/tracing/events/sched/sched_switch/trigger 2299 2300 When the histogram is displayed, the max value and the saved 2301 values corresponding to the max are displayed following the rest 2302 of the fields:: 2303 2304 # cat /sys/kernel/tracing/events/sched/sched_switch/hist 2305 { next_pid: 2255 } hitcount: 239 2306 common_timestamp-ts0: 0 2307 max: 27 2308 next_comm: cyclictest 2309 prev_pid: 0 prev_prio: 120 prev_comm: swapper/1 2310 2311 { next_pid: 2256 } hitcount: 2355 2312 common_timestamp-ts0: 0 2313 max: 49 next_comm: cyclictest 2314 prev_pid: 0 prev_prio: 120 prev_comm: swapper/0 2315 2316 Totals: 2317 Hits: 12970 2318 Entries: 2 2319 Dropped: 0 2320 2321 - onmax(var).snapshot() 2322 2323 The 'onmax(var).snapshot()' hist trigger action is invoked 2324 whenever the value of 'var' associated with a histogram entry 2325 exceeds the current maximum contained in that variable. 2326 2327 The end result is that a global snapshot of the trace buffer will 2328 be saved in the tracing/snapshot file if 'var' exceeds the current 2329 maximum for any hist trigger entry. 2330 2331 Note that in this case the maximum is a global maximum for the 2332 current trace instance, which is the maximum across all buckets of 2333 the histogram. The key of the specific trace event that caused 2334 the global maximum and the global maximum itself are displayed, 2335 along with a message stating that a snapshot has been taken and 2336 where to find it. The user can use the key information displayed 2337 to locate the corresponding bucket in the histogram for even more 2338 detail. 2339 2340 As an example the below defines a couple of hist triggers, one for 2341 sched_waking and another for sched_switch, keyed on pid. Whenever 2342 a sched_waking event occurs, the timestamp is saved in the entry 2343 corresponding to the current pid, and when the scheduler switches 2344 back to that pid, the timestamp difference is calculated. If the 2345 resulting latency, stored in wakeup_lat, exceeds the current 2346 maximum latency, a snapshot is taken. As part of the setup, all 2347 the scheduler events are also enabled, which are the events that 2348 will show up in the snapshot when it is taken at some point:: 2349 2350 # echo 1 > /sys/kernel/tracing/events/sched/enable 2351 2352 # echo 'hist:keys=pid:ts0=common_timestamp.usecs \ 2353 if comm=="cyclictest"' >> \ 2354 /sys/kernel/tracing/events/sched/sched_waking/trigger 2355 2356 # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0: \ 2357 onmax($wakeup_lat).save(next_prio,next_comm,prev_pid,prev_prio, \ 2358 prev_comm):onmax($wakeup_lat).snapshot() \ 2359 if next_comm=="cyclictest"' >> \ 2360 /sys/kernel/tracing/events/sched/sched_switch/trigger 2361 2362 When the histogram is displayed, for each bucket the max value 2363 and the saved values corresponding to the max are displayed 2364 following the rest of the fields. 2365 2366 If a snapshot was taken, there is also a message indicating that, 2367 along with the value and event that triggered the global maximum:: 2368 2369 # cat /sys/kernel/tracing/events/sched/sched_switch/hist 2370 { next_pid: 2101 } hitcount: 200 2371 max: 52 next_prio: 120 next_comm: cyclictest \ 2372 prev_pid: 0 prev_prio: 120 prev_comm: swapper/6 2373 2374 { next_pid: 2103 } hitcount: 1326 2375 max: 572 next_prio: 19 next_comm: cyclictest \ 2376 prev_pid: 0 prev_prio: 120 prev_comm: swapper/1 2377 2378 { next_pid: 2102 } hitcount: 1982 \ 2379 max: 74 next_prio: 19 next_comm: cyclictest \ 2380 prev_pid: 0 prev_prio: 120 prev_comm: swapper/5 2381 2382 Snapshot taken (see tracing/snapshot). Details: 2383 triggering value { onmax($wakeup_lat) }: 572 \ 2384 triggered by event with key: { next_pid: 2103 } 2385 2386 Totals: 2387 Hits: 3508 2388 Entries: 3 2389 Dropped: 0 2390 2391 In the above case, the event that triggered the global maximum has 2392 the key with next_pid == 2103. If you look at the bucket that has 2393 2103 as the key, you'll find the additional values save()'d along 2394 with the local maximum for that bucket, which should be the same 2395 as the global maximum (since that was the same value that 2396 triggered the global snapshot). 2397 2398 And finally, looking at the snapshot data should show at or near 2399 the end the event that triggered the snapshot (in this case you 2400 can verify the timestamps between the sched_waking and 2401 sched_switch events, which should match the time displayed in the 2402 global maximum):: 2403 2404 # cat /sys/kernel/tracing/snapshot 2405 2406 <...>-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 2407 <idle>-0 [005] d.h3 309.873611: sched_waking: comm=cyclictest pid=2102 prio=19 target_cpu=005 2408 <idle>-0 [005] dNh4 309.873613: sched_wakeup: comm=cyclictest pid=2102 prio=19 target_cpu=005 2409 <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 2410 <...>-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 2411 <idle>-0 [005] d.h3 309.874624: sched_waking: comm=cyclictest pid=2102 prio=19 target_cpu=005 2412 <idle>-0 [005] dNh4 309.874626: sched_wakeup: comm=cyclictest pid=2102 prio=19 target_cpu=005 2413 <idle>-0 [005] dNh3 309.874628: sched_waking: comm=cyclictest pid=2103 prio=19 target_cpu=005 2414 <idle>-0 [005] dNh4 309.874630: sched_wakeup: comm=cyclictest pid=2103 prio=19 target_cpu=005 2415 <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 2416 <idle>-0 [004] d.h3 309.874757: sched_waking: comm=gnome-terminal- pid=1699 prio=120 target_cpu=004 2417 <idle>-0 [004] dNh4 309.874762: sched_wakeup: comm=gnome-terminal- pid=1699 prio=120 target_cpu=004 2418 <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 2419 gnome-terminal--1699 [004] d.h2 309.874941: sched_stat_runtime: comm=gnome-terminal- pid=1699 runtime=180706 [ns] vruntime=1126870572 [ns] 2420 <idle>-0 [003] d.s4 309.874956: sched_waking: comm=rcu_sched pid=9 prio=120 target_cpu=007 2421 <idle>-0 [003] d.s5 309.874960: sched_wake_idle_without_ipi: cpu=7 2422 <idle>-0 [003] d.s5 309.874961: sched_wakeup: comm=rcu_sched pid=9 prio=120 target_cpu=007 2423 <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 2424 rcu_sched-9 [007] d..3 309.874973: sched_stat_runtime: comm=rcu_sched pid=9 runtime=13646 [ns] vruntime=22531430286 [ns] 2425 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 2426 <...>-2102 [005] d..4 309.874994: sched_migrate_task: comm=cyclictest pid=2103 prio=19 orig_cpu=5 dest_cpu=1 2427 <...>-2102 [005] d..4 309.875185: sched_wake_idle_without_ipi: cpu=1 2428 <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 2429 2430 - onchange(var).save(field,.. .) 2431 2432 The 'onchange(var).save(field,...)' hist trigger action is invoked 2433 whenever the value of 'var' associated with a histogram entry 2434 changes. 2435 2436 The end result is that the trace event fields specified as the 2437 onchange.save() params will be saved if 'var' changes for that 2438 hist trigger entry. This allows context from the event that 2439 changed the value to be saved for later reference. When the 2440 histogram is displayed, additional fields displaying the saved 2441 values will be printed. 2442 2443 - onchange(var).snapshot() 2444 2445 The 'onchange(var).snapshot()' hist trigger action is invoked 2446 whenever the value of 'var' associated with a histogram entry 2447 changes. 2448 2449 The end result is that a global snapshot of the trace buffer will 2450 be saved in the tracing/snapshot file if 'var' changes for any 2451 hist trigger entry. 2452 2453 Note that in this case the changed value is a global variable 2454 associated with current trace instance. The key of the specific 2455 trace event that caused the value to change and the global value 2456 itself are displayed, along with a message stating that a snapshot 2457 has been taken and where to find it. The user can use the key 2458 information displayed to locate the corresponding bucket in the 2459 histogram for even more detail. 2460 2461 As an example the below defines a hist trigger on the tcp_probe 2462 event, keyed on dport. Whenever a tcp_probe event occurs, the 2463 cwnd field is checked against the current value stored in the 2464 $cwnd variable. If the value has changed, a snapshot is taken. 2465 As part of the setup, all the scheduler and tcp events are also 2466 enabled, which are the events that will show up in the snapshot 2467 when it is taken at some point:: 2468 2469 # echo 1 > /sys/kernel/tracing/events/sched/enable 2470 # echo 1 > /sys/kernel/tracing/events/tcp/enable 2471 2472 # echo 'hist:keys=dport:cwnd=snd_cwnd: \ 2473 onchange($cwnd).save(snd_wnd,srtt,rcv_wnd): \ 2474 onchange($cwnd).snapshot()' >> \ 2475 /sys/kernel/tracing/events/tcp/tcp_probe/trigger 2476 2477 When the histogram is displayed, for each bucket the tracked value 2478 and the saved values corresponding to that value are displayed 2479 following the rest of the fields. 2480 2481 If a snapshot was taken, there is also a message indicating that, 2482 along with the value and event that triggered the snapshot:: 2483 2484 # cat /sys/kernel/tracing/events/tcp/tcp_probe/hist 2485 2486 { dport: 1521 } hitcount: 8 2487 changed: 10 snd_wnd: 35456 srtt: 154262 rcv_wnd: 42112 2488 2489 { dport: 80 } hitcount: 23 2490 changed: 10 snd_wnd: 28960 srtt: 19604 rcv_wnd: 29312 2491 2492 { dport: 9001 } hitcount: 172 2493 changed: 10 snd_wnd: 48384 srtt: 260444 rcv_wnd: 55168 2494 2495 { dport: 443 } hitcount: 211 2496 changed: 10 snd_wnd: 26960 srtt: 17379 rcv_wnd: 28800 2497 2498 Snapshot taken (see tracing/snapshot). Details: 2499 2500 triggering value { onchange($cwnd) }: 10 2501 triggered by event with key: { dport: 80 } 2502 2503 Totals: 2504 Hits: 414 2505 Entries: 4 2506 Dropped: 0 2507 2508 In the above case, the event that triggered the snapshot has the 2509 key with dport == 80. If you look at the bucket that has 80 as 2510 the key, you'll find the additional values save()'d along with the 2511 changed value for that bucket, which should be the same as the 2512 global changed value (since that was the same value that triggered 2513 the global snapshot). 2514 2515 And finally, looking at the snapshot data should show at or near 2516 the end the event that triggered the snapshot:: 2517 2518 # cat /sys/kernel/tracing/snapshot 2519 2520 gnome-shell-1261 [006] dN.3 49.823113: sched_stat_runtime: comm=gnome-shell pid=1261 runtime=49347 [ns] vruntime=1835730389 [ns] 2521 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 2522 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 2523 kworker/3:2-135 [003] d..3 49.823118: sched_stat_runtime: comm=kworker/3:2 pid=135 runtime=5339 [ns] vruntime=17815800388 [ns] 2524 kworker/6:2-387 [006] d..3 49.823120: sched_stat_runtime: comm=kworker/6:2 pid=387 runtime=9594 [ns] vruntime=14589605367 [ns] 2525 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 2526 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 2527 <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 2528 25293. User space creating a trigger 2530-------------------------------- 2531 2532Writing into /sys/kernel/tracing/trace_marker writes into the ftrace 2533ring buffer. This can also act like an event, by writing into the trigger 2534file located in /sys/kernel/tracing/events/ftrace/print/ 2535 2536Modifying cyclictest to write into the trace_marker file before it sleeps 2537and after it wakes up, something like this:: 2538 2539 static void traceputs(char *str) 2540 { 2541 /* tracemark_fd is the trace_marker file descriptor */ 2542 if (tracemark_fd < 0) 2543 return; 2544 /* write the tracemark message */ 2545 write(tracemark_fd, str, strlen(str)); 2546 } 2547 2548And later add something like:: 2549 2550 traceputs("start"); 2551 clock_nanosleep(...); 2552 traceputs("end"); 2553 2554We can make a histogram from this:: 2555 2556 # cd /sys/kernel/tracing 2557 # echo 'latency u64 lat' > synthetic_events 2558 # echo 'hist:keys=common_pid:ts0=common_timestamp.usecs if buf == "start"' > events/ftrace/print/trigger 2559 # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(ftrace.print).latency($lat) if buf == "end"' >> events/ftrace/print/trigger 2560 # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger 2561 2562The above created a synthetic event called "latency" and two histograms 2563against the trace_marker, one gets triggered when "start" is written into the 2564trace_marker file and the other when "end" is written. If the pids match, then 2565it will call the "latency" synthetic event with the calculated latency as its 2566parameter. Finally, a histogram is added to the latency synthetic event to 2567record the calculated latency along with the pid. 2568 2569Now running cyclictest with:: 2570 2571 # ./cyclictest -p80 -d0 -i250 -n -a -t --tracemark -b 1000 2572 2573 -p80 : run threads at priority 80 2574 -d0 : have all threads run at the same interval 2575 -i250 : start the interval at 250 microseconds (all threads will do this) 2576 -n : sleep with nanosleep 2577 -a : affine all threads to a separate CPU 2578 -t : one thread per available CPU 2579 --tracemark : enable trace mark writing 2580 -b 1000 : stop if any latency is greater than 1000 microseconds 2581 2582Note, the -b 1000 is used just to make --tracemark available. 2583 2584Then we can see the histogram created by this with:: 2585 2586 # cat events/synthetic/latency/hist 2587 # event histogram 2588 # 2589 # trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active] 2590 # 2591 2592 { lat: 107, common_pid: 2039 } hitcount: 1 2593 { lat: 122, common_pid: 2041 } hitcount: 1 2594 { lat: 166, common_pid: 2039 } hitcount: 1 2595 { lat: 174, common_pid: 2039 } hitcount: 1 2596 { lat: 194, common_pid: 2041 } hitcount: 1 2597 { lat: 196, common_pid: 2036 } hitcount: 1 2598 { lat: 197, common_pid: 2038 } hitcount: 1 2599 { lat: 198, common_pid: 2039 } hitcount: 1 2600 { lat: 199, common_pid: 2039 } hitcount: 1 2601 { lat: 200, common_pid: 2041 } hitcount: 1 2602 { lat: 201, common_pid: 2039 } hitcount: 2 2603 { lat: 202, common_pid: 2038 } hitcount: 1 2604 { lat: 202, common_pid: 2043 } hitcount: 1 2605 { lat: 203, common_pid: 2039 } hitcount: 1 2606 { lat: 203, common_pid: 2036 } hitcount: 1 2607 { lat: 203, common_pid: 2041 } hitcount: 1 2608 { lat: 206, common_pid: 2038 } hitcount: 2 2609 { lat: 207, common_pid: 2039 } hitcount: 1 2610 { lat: 207, common_pid: 2036 } hitcount: 1 2611 { lat: 208, common_pid: 2040 } hitcount: 1 2612 { lat: 209, common_pid: 2043 } hitcount: 1 2613 { lat: 210, common_pid: 2039 } hitcount: 1 2614 { lat: 211, common_pid: 2039 } hitcount: 4 2615 { lat: 212, common_pid: 2043 } hitcount: 1 2616 { lat: 212, common_pid: 2039 } hitcount: 2 2617 { lat: 213, common_pid: 2039 } hitcount: 1 2618 { lat: 214, common_pid: 2038 } hitcount: 1 2619 { lat: 214, common_pid: 2039 } hitcount: 2 2620 { lat: 214, common_pid: 2042 } hitcount: 1 2621 { lat: 215, common_pid: 2039 } hitcount: 1 2622 { lat: 217, common_pid: 2036 } hitcount: 1 2623 { lat: 217, common_pid: 2040 } hitcount: 1 2624 { lat: 217, common_pid: 2039 } hitcount: 1 2625 { lat: 218, common_pid: 2039 } hitcount: 6 2626 { lat: 219, common_pid: 2039 } hitcount: 9 2627 { lat: 220, common_pid: 2039 } hitcount: 11 2628 { lat: 221, common_pid: 2039 } hitcount: 5 2629 { lat: 221, common_pid: 2042 } hitcount: 1 2630 { lat: 222, common_pid: 2039 } hitcount: 7 2631 { lat: 223, common_pid: 2036 } hitcount: 1 2632 { lat: 223, common_pid: 2039 } hitcount: 3 2633 { lat: 224, common_pid: 2039 } hitcount: 4 2634 { lat: 224, common_pid: 2037 } hitcount: 1 2635 { lat: 224, common_pid: 2036 } hitcount: 2 2636 { lat: 225, common_pid: 2039 } hitcount: 5 2637 { lat: 225, common_pid: 2042 } hitcount: 1 2638 { lat: 226, common_pid: 2039 } hitcount: 7 2639 { lat: 226, common_pid: 2036 } hitcount: 4 2640 { lat: 227, common_pid: 2039 } hitcount: 6 2641 { lat: 227, common_pid: 2036 } hitcount: 12 2642 { lat: 227, common_pid: 2043 } hitcount: 1 2643 { lat: 228, common_pid: 2039 } hitcount: 7 2644 { lat: 228, common_pid: 2036 } hitcount: 14 2645 { lat: 229, common_pid: 2039 } hitcount: 9 2646 { lat: 229, common_pid: 2036 } hitcount: 8 2647 { lat: 229, common_pid: 2038 } hitcount: 1 2648 { lat: 230, common_pid: 2039 } hitcount: 11 2649 { lat: 230, common_pid: 2036 } hitcount: 6 2650 { lat: 230, common_pid: 2043 } hitcount: 1 2651 { lat: 230, common_pid: 2042 } hitcount: 2 2652 { lat: 231, common_pid: 2041 } hitcount: 1 2653 { lat: 231, common_pid: 2036 } hitcount: 6 2654 { lat: 231, common_pid: 2043 } hitcount: 1 2655 { lat: 231, common_pid: 2039 } hitcount: 8 2656 { lat: 232, common_pid: 2037 } hitcount: 1 2657 { lat: 232, common_pid: 2039 } hitcount: 6 2658 { lat: 232, common_pid: 2040 } hitcount: 2 2659 { lat: 232, common_pid: 2036 } hitcount: 5 2660 { lat: 232, common_pid: 2043 } hitcount: 1 2661 { lat: 233, common_pid: 2036 } hitcount: 5 2662 { lat: 233, common_pid: 2039 } hitcount: 11 2663 { lat: 234, common_pid: 2039 } hitcount: 4 2664 { lat: 234, common_pid: 2038 } hitcount: 2 2665 { lat: 234, common_pid: 2043 } hitcount: 2 2666 { lat: 234, common_pid: 2036 } hitcount: 11 2667 { lat: 234, common_pid: 2040 } hitcount: 1 2668 { lat: 235, common_pid: 2037 } hitcount: 2 2669 { lat: 235, common_pid: 2036 } hitcount: 8 2670 { lat: 235, common_pid: 2043 } hitcount: 2 2671 { lat: 235, common_pid: 2039 } hitcount: 5 2672 { lat: 235, common_pid: 2042 } hitcount: 2 2673 { lat: 235, common_pid: 2040 } hitcount: 4 2674 { lat: 235, common_pid: 2041 } hitcount: 1 2675 { lat: 236, common_pid: 2036 } hitcount: 7 2676 { lat: 236, common_pid: 2037 } hitcount: 1 2677 { lat: 236, common_pid: 2041 } hitcount: 5 2678 { lat: 236, common_pid: 2039 } hitcount: 3 2679 { lat: 236, common_pid: 2043 } hitcount: 9 2680 { lat: 236, common_pid: 2040 } hitcount: 7 2681 { lat: 237, common_pid: 2037 } hitcount: 1 2682 { lat: 237, common_pid: 2040 } hitcount: 1 2683 { lat: 237, common_pid: 2036 } hitcount: 9 2684 { lat: 237, common_pid: 2039 } hitcount: 3 2685 { lat: 237, common_pid: 2043 } hitcount: 8 2686 { lat: 237, common_pid: 2042 } hitcount: 2 2687 { lat: 237, common_pid: 2041 } hitcount: 2 2688 { lat: 238, common_pid: 2043 } hitcount: 10 2689 { lat: 238, common_pid: 2040 } hitcount: 1 2690 { lat: 238, common_pid: 2037 } hitcount: 9 2691 { lat: 238, common_pid: 2038 } hitcount: 1 2692 { lat: 238, common_pid: 2039 } hitcount: 1 2693 { lat: 238, common_pid: 2042 } hitcount: 3 2694 { lat: 238, common_pid: 2036 } hitcount: 7 2695 { lat: 239, common_pid: 2041 } hitcount: 1 2696 { lat: 239, common_pid: 2043 } hitcount: 11 2697 { lat: 239, common_pid: 2037 } hitcount: 11 2698 { lat: 239, common_pid: 2038 } hitcount: 6 2699 { lat: 239, common_pid: 2036 } hitcount: 7 2700 { lat: 239, common_pid: 2040 } hitcount: 1 2701 { lat: 239, common_pid: 2042 } hitcount: 9 2702 { lat: 240, common_pid: 2037 } hitcount: 29 2703 { lat: 240, common_pid: 2043 } hitcount: 15 2704 { lat: 240, common_pid: 2040 } hitcount: 44 2705 { lat: 240, common_pid: 2039 } hitcount: 1 2706 { lat: 240, common_pid: 2041 } hitcount: 2 2707 { lat: 240, common_pid: 2038 } hitcount: 1 2708 { lat: 240, common_pid: 2036 } hitcount: 10 2709 { lat: 240, common_pid: 2042 } hitcount: 13 2710 { lat: 241, common_pid: 2036 } hitcount: 21 2711 { lat: 241, common_pid: 2041 } hitcount: 36 2712 { lat: 241, common_pid: 2037 } hitcount: 34 2713 { lat: 241, common_pid: 2042 } hitcount: 14 2714 { lat: 241, common_pid: 2040 } hitcount: 94 2715 { lat: 241, common_pid: 2039 } hitcount: 12 2716 { lat: 241, common_pid: 2038 } hitcount: 2 2717 { lat: 241, common_pid: 2043 } hitcount: 28 2718 { lat: 242, common_pid: 2040 } hitcount: 109 2719 { lat: 242, common_pid: 2041 } hitcount: 506 2720 { lat: 242, common_pid: 2039 } hitcount: 155 2721 { lat: 242, common_pid: 2042 } hitcount: 21 2722 { lat: 242, common_pid: 2037 } hitcount: 52 2723 { lat: 242, common_pid: 2043 } hitcount: 21 2724 { lat: 242, common_pid: 2036 } hitcount: 16 2725 { lat: 242, common_pid: 2038 } hitcount: 156 2726 { lat: 243, common_pid: 2037 } hitcount: 46 2727 { lat: 243, common_pid: 2039 } hitcount: 40 2728 { lat: 243, common_pid: 2042 } hitcount: 119 2729 { lat: 243, common_pid: 2041 } hitcount: 611 2730 { lat: 243, common_pid: 2036 } hitcount: 69 2731 { lat: 243, common_pid: 2038 } hitcount: 784 2732 { lat: 243, common_pid: 2040 } hitcount: 323 2733 { lat: 243, common_pid: 2043 } hitcount: 14 2734 { lat: 244, common_pid: 2043 } hitcount: 35 2735 { lat: 244, common_pid: 2042 } hitcount: 305 2736 { lat: 244, common_pid: 2039 } hitcount: 8 2737 { lat: 244, common_pid: 2040 } hitcount: 4515 2738 { lat: 244, common_pid: 2038 } hitcount: 371 2739 { lat: 244, common_pid: 2037 } hitcount: 31 2740 { lat: 244, common_pid: 2036 } hitcount: 114 2741 { lat: 244, common_pid: 2041 } hitcount: 3396 2742 { lat: 245, common_pid: 2036 } hitcount: 700 2743 { lat: 245, common_pid: 2041 } hitcount: 2772 2744 { lat: 245, common_pid: 2037 } hitcount: 268 2745 { lat: 245, common_pid: 2039 } hitcount: 472 2746 { lat: 245, common_pid: 2038 } hitcount: 2758 2747 { lat: 245, common_pid: 2042 } hitcount: 3833 2748 { lat: 245, common_pid: 2040 } hitcount: 3105 2749 { lat: 245, common_pid: 2043 } hitcount: 645 2750 { lat: 246, common_pid: 2038 } hitcount: 3451 2751 { lat: 246, common_pid: 2041 } hitcount: 142 2752 { lat: 246, common_pid: 2037 } hitcount: 5101 2753 { lat: 246, common_pid: 2040 } hitcount: 68 2754 { lat: 246, common_pid: 2043 } hitcount: 5099 2755 { lat: 246, common_pid: 2039 } hitcount: 5608 2756 { lat: 246, common_pid: 2042 } hitcount: 3723 2757 { lat: 246, common_pid: 2036 } hitcount: 4738 2758 { lat: 247, common_pid: 2042 } hitcount: 312 2759 { lat: 247, common_pid: 2043 } hitcount: 2385 2760 { lat: 247, common_pid: 2041 } hitcount: 452 2761 { lat: 247, common_pid: 2038 } hitcount: 792 2762 { lat: 247, common_pid: 2040 } hitcount: 78 2763 { lat: 247, common_pid: 2036 } hitcount: 2375 2764 { lat: 247, common_pid: 2039 } hitcount: 1834 2765 { lat: 247, common_pid: 2037 } hitcount: 2655 2766 { lat: 248, common_pid: 2037 } hitcount: 36 2767 { lat: 248, common_pid: 2042 } hitcount: 11 2768 { lat: 248, common_pid: 2038 } hitcount: 122 2769 { lat: 248, common_pid: 2036 } hitcount: 135 2770 { lat: 248, common_pid: 2039 } hitcount: 26 2771 { lat: 248, common_pid: 2041 } hitcount: 503 2772 { lat: 248, common_pid: 2043 } hitcount: 66 2773 { lat: 248, common_pid: 2040 } hitcount: 46 2774 { lat: 249, common_pid: 2037 } hitcount: 29 2775 { lat: 249, common_pid: 2038 } hitcount: 1 2776 { lat: 249, common_pid: 2043 } hitcount: 29 2777 { lat: 249, common_pid: 2039 } hitcount: 8 2778 { lat: 249, common_pid: 2042 } hitcount: 56 2779 { lat: 249, common_pid: 2040 } hitcount: 27 2780 { lat: 249, common_pid: 2041 } hitcount: 11 2781 { lat: 249, common_pid: 2036 } hitcount: 27 2782 { lat: 250, common_pid: 2038 } hitcount: 1 2783 { lat: 250, common_pid: 2036 } hitcount: 30 2784 { lat: 250, common_pid: 2040 } hitcount: 19 2785 { lat: 250, common_pid: 2043 } hitcount: 22 2786 { lat: 250, common_pid: 2042 } hitcount: 20 2787 { lat: 250, common_pid: 2041 } hitcount: 1 2788 { lat: 250, common_pid: 2039 } hitcount: 6 2789 { lat: 250, common_pid: 2037 } hitcount: 48 2790 { lat: 251, common_pid: 2037 } hitcount: 43 2791 { lat: 251, common_pid: 2039 } hitcount: 1 2792 { lat: 251, common_pid: 2036 } hitcount: 12 2793 { lat: 251, common_pid: 2042 } hitcount: 2 2794 { lat: 251, common_pid: 2041 } hitcount: 1 2795 { lat: 251, common_pid: 2043 } hitcount: 15 2796 { lat: 251, common_pid: 2040 } hitcount: 3 2797 { lat: 252, common_pid: 2040 } hitcount: 1 2798 { lat: 252, common_pid: 2036 } hitcount: 12 2799 { lat: 252, common_pid: 2037 } hitcount: 21 2800 { lat: 252, common_pid: 2043 } hitcount: 14 2801 { lat: 253, common_pid: 2037 } hitcount: 21 2802 { lat: 253, common_pid: 2039 } hitcount: 2 2803 { lat: 253, common_pid: 2036 } hitcount: 9 2804 { lat: 253, common_pid: 2043 } hitcount: 6 2805 { lat: 253, common_pid: 2040 } hitcount: 1 2806 { lat: 254, common_pid: 2036 } hitcount: 8 2807 { lat: 254, common_pid: 2043 } hitcount: 3 2808 { lat: 254, common_pid: 2041 } hitcount: 1 2809 { lat: 254, common_pid: 2042 } hitcount: 1 2810 { lat: 254, common_pid: 2039 } hitcount: 1 2811 { lat: 254, common_pid: 2037 } hitcount: 12 2812 { lat: 255, common_pid: 2043 } hitcount: 1 2813 { lat: 255, common_pid: 2037 } hitcount: 2 2814 { lat: 255, common_pid: 2036 } hitcount: 2 2815 { lat: 255, common_pid: 2039 } hitcount: 8 2816 { lat: 256, common_pid: 2043 } hitcount: 1 2817 { lat: 256, common_pid: 2036 } hitcount: 4 2818 { lat: 256, common_pid: 2039 } hitcount: 6 2819 { lat: 257, common_pid: 2039 } hitcount: 5 2820 { lat: 257, common_pid: 2036 } hitcount: 4 2821 { lat: 258, common_pid: 2039 } hitcount: 5 2822 { lat: 258, common_pid: 2036 } hitcount: 2 2823 { lat: 259, common_pid: 2036 } hitcount: 7 2824 { lat: 259, common_pid: 2039 } hitcount: 7 2825 { lat: 260, common_pid: 2036 } hitcount: 8 2826 { lat: 260, common_pid: 2039 } hitcount: 6 2827 { lat: 261, common_pid: 2036 } hitcount: 5 2828 { lat: 261, common_pid: 2039 } hitcount: 7 2829 { lat: 262, common_pid: 2039 } hitcount: 5 2830 { lat: 262, common_pid: 2036 } hitcount: 5 2831 { lat: 263, common_pid: 2039 } hitcount: 7 2832 { lat: 263, common_pid: 2036 } hitcount: 7 2833 { lat: 264, common_pid: 2039 } hitcount: 9 2834 { lat: 264, common_pid: 2036 } hitcount: 9 2835 { lat: 265, common_pid: 2036 } hitcount: 5 2836 { lat: 265, common_pid: 2039 } hitcount: 1 2837 { lat: 266, common_pid: 2036 } hitcount: 1 2838 { lat: 266, common_pid: 2039 } hitcount: 3 2839 { lat: 267, common_pid: 2036 } hitcount: 1 2840 { lat: 267, common_pid: 2039 } hitcount: 3 2841 { lat: 268, common_pid: 2036 } hitcount: 1 2842 { lat: 268, common_pid: 2039 } hitcount: 6 2843 { lat: 269, common_pid: 2036 } hitcount: 1 2844 { lat: 269, common_pid: 2043 } hitcount: 1 2845 { lat: 269, common_pid: 2039 } hitcount: 2 2846 { lat: 270, common_pid: 2040 } hitcount: 1 2847 { lat: 270, common_pid: 2039 } hitcount: 6 2848 { lat: 271, common_pid: 2041 } hitcount: 1 2849 { lat: 271, common_pid: 2039 } hitcount: 5 2850 { lat: 272, common_pid: 2039 } hitcount: 10 2851 { lat: 273, common_pid: 2039 } hitcount: 8 2852 { lat: 274, common_pid: 2039 } hitcount: 2 2853 { lat: 275, common_pid: 2039 } hitcount: 1 2854 { lat: 276, common_pid: 2039 } hitcount: 2 2855 { lat: 276, common_pid: 2037 } hitcount: 1 2856 { lat: 276, common_pid: 2038 } hitcount: 1 2857 { lat: 277, common_pid: 2039 } hitcount: 1 2858 { lat: 277, common_pid: 2042 } hitcount: 1 2859 { lat: 278, common_pid: 2039 } hitcount: 1 2860 { lat: 279, common_pid: 2039 } hitcount: 4 2861 { lat: 279, common_pid: 2043 } hitcount: 1 2862 { lat: 280, common_pid: 2039 } hitcount: 3 2863 { lat: 283, common_pid: 2036 } hitcount: 2 2864 { lat: 284, common_pid: 2039 } hitcount: 1 2865 { lat: 284, common_pid: 2043 } hitcount: 1 2866 { lat: 288, common_pid: 2039 } hitcount: 1 2867 { lat: 289, common_pid: 2039 } hitcount: 1 2868 { lat: 300, common_pid: 2039 } hitcount: 1 2869 { lat: 384, common_pid: 2039 } hitcount: 1 2870 2871 Totals: 2872 Hits: 67625 2873 Entries: 278 2874 Dropped: 0 2875 2876Note, the writes are around the sleep, so ideally they will all be of 250 2877microseconds. If you are wondering how there are several that are under 2878250 microseconds, that is because the way cyclictest works, is if one 2879iteration comes in late, the next one will set the timer to wake up less that 2880250. That is, if an iteration came in 50 microseconds late, the next wake up 2881will be at 200 microseconds. 2882 2883But this could easily be done in userspace. To make this even more 2884interesting, we can mix the histogram between events that happened in the 2885kernel with trace_marker:: 2886 2887 # cd /sys/kernel/tracing 2888 # echo 'latency u64 lat' > synthetic_events 2889 # echo 'hist:keys=pid:ts0=common_timestamp.usecs' > events/sched/sched_waking/trigger 2890 # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(sched.sched_waking).latency($lat) if buf == "end"' > events/ftrace/print/trigger 2891 # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger 2892 2893The difference this time is that instead of using the trace_marker to start 2894the latency, the sched_waking event is used, matching the common_pid for the 2895trace_marker write with the pid that is being woken by sched_waking. 2896 2897After running cyclictest again with the same parameters, we now have:: 2898 2899 # cat events/synthetic/latency/hist 2900 # event histogram 2901 # 2902 # trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active] 2903 # 2904 2905 { lat: 7, common_pid: 2302 } hitcount: 640 2906 { lat: 7, common_pid: 2299 } hitcount: 42 2907 { lat: 7, common_pid: 2303 } hitcount: 18 2908 { lat: 7, common_pid: 2305 } hitcount: 166 2909 { lat: 7, common_pid: 2306 } hitcount: 1 2910 { lat: 7, common_pid: 2301 } hitcount: 91 2911 { lat: 7, common_pid: 2300 } hitcount: 17 2912 { lat: 8, common_pid: 2303 } hitcount: 8296 2913 { lat: 8, common_pid: 2304 } hitcount: 6864 2914 { lat: 8, common_pid: 2305 } hitcount: 9464 2915 { lat: 8, common_pid: 2301 } hitcount: 9213 2916 { lat: 8, common_pid: 2306 } hitcount: 6246 2917 { lat: 8, common_pid: 2302 } hitcount: 8797 2918 { lat: 8, common_pid: 2299 } hitcount: 8771 2919 { lat: 8, common_pid: 2300 } hitcount: 8119 2920 { lat: 9, common_pid: 2305 } hitcount: 1519 2921 { lat: 9, common_pid: 2299 } hitcount: 2346 2922 { lat: 9, common_pid: 2303 } hitcount: 2841 2923 { lat: 9, common_pid: 2301 } hitcount: 1846 2924 { lat: 9, common_pid: 2304 } hitcount: 3861 2925 { lat: 9, common_pid: 2302 } hitcount: 1210 2926 { lat: 9, common_pid: 2300 } hitcount: 2762 2927 { lat: 9, common_pid: 2306 } hitcount: 4247 2928 { lat: 10, common_pid: 2299 } hitcount: 16 2929 { lat: 10, common_pid: 2306 } hitcount: 333 2930 { lat: 10, common_pid: 2303 } hitcount: 16 2931 { lat: 10, common_pid: 2304 } hitcount: 168 2932 { lat: 10, common_pid: 2302 } hitcount: 240 2933 { lat: 10, common_pid: 2301 } hitcount: 28 2934 { lat: 10, common_pid: 2300 } hitcount: 95 2935 { lat: 10, common_pid: 2305 } hitcount: 18 2936 { lat: 11, common_pid: 2303 } hitcount: 5 2937 { lat: 11, common_pid: 2305 } hitcount: 8 2938 { lat: 11, common_pid: 2306 } hitcount: 221 2939 { lat: 11, common_pid: 2302 } hitcount: 76 2940 { lat: 11, common_pid: 2304 } hitcount: 26 2941 { lat: 11, common_pid: 2300 } hitcount: 125 2942 { lat: 11, common_pid: 2299 } hitcount: 2 2943 { lat: 12, common_pid: 2305 } hitcount: 3 2944 { lat: 12, common_pid: 2300 } hitcount: 6 2945 { lat: 12, common_pid: 2306 } hitcount: 90 2946 { lat: 12, common_pid: 2302 } hitcount: 4 2947 { lat: 12, common_pid: 2303 } hitcount: 1 2948 { lat: 12, common_pid: 2304 } hitcount: 122 2949 { lat: 13, common_pid: 2300 } hitcount: 12 2950 { lat: 13, common_pid: 2301 } hitcount: 1 2951 { lat: 13, common_pid: 2306 } hitcount: 32 2952 { lat: 13, common_pid: 2302 } hitcount: 5 2953 { lat: 13, common_pid: 2305 } hitcount: 1 2954 { lat: 13, common_pid: 2303 } hitcount: 1 2955 { lat: 13, common_pid: 2304 } hitcount: 61 2956 { lat: 14, common_pid: 2303 } hitcount: 4 2957 { lat: 14, common_pid: 2306 } hitcount: 5 2958 { lat: 14, common_pid: 2305 } hitcount: 4 2959 { lat: 14, common_pid: 2304 } hitcount: 62 2960 { lat: 14, common_pid: 2302 } hitcount: 19 2961 { lat: 14, common_pid: 2300 } hitcount: 33 2962 { lat: 14, common_pid: 2299 } hitcount: 1 2963 { lat: 14, common_pid: 2301 } hitcount: 4 2964 { lat: 15, common_pid: 2305 } hitcount: 1 2965 { lat: 15, common_pid: 2302 } hitcount: 25 2966 { lat: 15, common_pid: 2300 } hitcount: 11 2967 { lat: 15, common_pid: 2299 } hitcount: 5 2968 { lat: 15, common_pid: 2301 } hitcount: 1 2969 { lat: 15, common_pid: 2304 } hitcount: 8 2970 { lat: 15, common_pid: 2303 } hitcount: 1 2971 { lat: 15, common_pid: 2306 } hitcount: 6 2972 { lat: 16, common_pid: 2302 } hitcount: 31 2973 { lat: 16, common_pid: 2306 } hitcount: 3 2974 { lat: 16, common_pid: 2300 } hitcount: 5 2975 { lat: 17, common_pid: 2302 } hitcount: 6 2976 { lat: 17, common_pid: 2303 } hitcount: 1 2977 { lat: 18, common_pid: 2304 } hitcount: 1 2978 { lat: 18, common_pid: 2302 } hitcount: 8 2979 { lat: 18, common_pid: 2299 } hitcount: 1 2980 { lat: 18, common_pid: 2301 } hitcount: 1 2981 { lat: 19, common_pid: 2303 } hitcount: 4 2982 { lat: 19, common_pid: 2304 } hitcount: 5 2983 { lat: 19, common_pid: 2302 } hitcount: 4 2984 { lat: 19, common_pid: 2299 } hitcount: 3 2985 { lat: 19, common_pid: 2306 } hitcount: 1 2986 { lat: 19, common_pid: 2300 } hitcount: 4 2987 { lat: 19, common_pid: 2305 } hitcount: 5 2988 { lat: 20, common_pid: 2299 } hitcount: 2 2989 { lat: 20, common_pid: 2302 } hitcount: 3 2990 { lat: 20, common_pid: 2305 } hitcount: 1 2991 { lat: 20, common_pid: 2300 } hitcount: 2 2992 { lat: 20, common_pid: 2301 } hitcount: 2 2993 { lat: 20, common_pid: 2303 } hitcount: 3 2994 { lat: 21, common_pid: 2305 } hitcount: 1 2995 { lat: 21, common_pid: 2299 } hitcount: 5 2996 { lat: 21, common_pid: 2303 } hitcount: 4 2997 { lat: 21, common_pid: 2302 } hitcount: 7 2998 { lat: 21, common_pid: 2300 } hitcount: 1 2999 { lat: 21, common_pid: 2301 } hitcount: 5 3000 { lat: 21, common_pid: 2304 } hitcount: 2 3001 { lat: 22, common_pid: 2302 } hitcount: 5 3002 { lat: 22, common_pid: 2303 } hitcount: 1 3003 { lat: 22, common_pid: 2306 } hitcount: 3 3004 { lat: 22, common_pid: 2301 } hitcount: 2 3005 { lat: 22, common_pid: 2300 } hitcount: 1 3006 { lat: 22, common_pid: 2299 } hitcount: 1 3007 { lat: 22, common_pid: 2305 } hitcount: 1 3008 { lat: 22, common_pid: 2304 } hitcount: 1 3009 { lat: 23, common_pid: 2299 } hitcount: 1 3010 { lat: 23, common_pid: 2306 } hitcount: 2 3011 { lat: 23, common_pid: 2302 } hitcount: 6 3012 { lat: 24, common_pid: 2302 } hitcount: 3 3013 { lat: 24, common_pid: 2300 } hitcount: 1 3014 { lat: 24, common_pid: 2306 } hitcount: 2 3015 { lat: 24, common_pid: 2305 } hitcount: 1 3016 { lat: 24, common_pid: 2299 } hitcount: 1 3017 { lat: 25, common_pid: 2300 } hitcount: 1 3018 { lat: 25, common_pid: 2302 } hitcount: 4 3019 { lat: 26, common_pid: 2302 } hitcount: 2 3020 { lat: 27, common_pid: 2305 } hitcount: 1 3021 { lat: 27, common_pid: 2300 } hitcount: 1 3022 { lat: 27, common_pid: 2302 } hitcount: 3 3023 { lat: 28, common_pid: 2306 } hitcount: 1 3024 { lat: 28, common_pid: 2302 } hitcount: 4 3025 { lat: 29, common_pid: 2302 } hitcount: 1 3026 { lat: 29, common_pid: 2300 } hitcount: 2 3027 { lat: 29, common_pid: 2306 } hitcount: 1 3028 { lat: 29, common_pid: 2304 } hitcount: 1 3029 { lat: 30, common_pid: 2302 } hitcount: 4 3030 { lat: 31, common_pid: 2302 } hitcount: 6 3031 { lat: 32, common_pid: 2302 } hitcount: 1 3032 { lat: 33, common_pid: 2299 } hitcount: 1 3033 { lat: 33, common_pid: 2302 } hitcount: 3 3034 { lat: 34, common_pid: 2302 } hitcount: 2 3035 { lat: 35, common_pid: 2302 } hitcount: 1 3036 { lat: 35, common_pid: 2304 } hitcount: 1 3037 { lat: 36, common_pid: 2302 } hitcount: 4 3038 { lat: 37, common_pid: 2302 } hitcount: 6 3039 { lat: 38, common_pid: 2302 } hitcount: 2 3040 { lat: 39, common_pid: 2302 } hitcount: 2 3041 { lat: 39, common_pid: 2304 } hitcount: 1 3042 { lat: 40, common_pid: 2304 } hitcount: 2 3043 { lat: 40, common_pid: 2302 } hitcount: 5 3044 { lat: 41, common_pid: 2304 } hitcount: 1 3045 { lat: 41, common_pid: 2302 } hitcount: 8 3046 { lat: 42, common_pid: 2302 } hitcount: 6 3047 { lat: 42, common_pid: 2304 } hitcount: 1 3048 { lat: 43, common_pid: 2302 } hitcount: 3 3049 { lat: 43, common_pid: 2304 } hitcount: 4 3050 { lat: 44, common_pid: 2302 } hitcount: 6 3051 { lat: 45, common_pid: 2302 } hitcount: 5 3052 { lat: 46, common_pid: 2302 } hitcount: 5 3053 { lat: 47, common_pid: 2302 } hitcount: 7 3054 { lat: 48, common_pid: 2301 } hitcount: 1 3055 { lat: 48, common_pid: 2302 } hitcount: 9 3056 { lat: 49, common_pid: 2302 } hitcount: 3 3057 { lat: 50, common_pid: 2302 } hitcount: 1 3058 { lat: 50, common_pid: 2301 } hitcount: 1 3059 { lat: 51, common_pid: 2302 } hitcount: 2 3060 { lat: 51, common_pid: 2301 } hitcount: 1 3061 { lat: 61, common_pid: 2302 } hitcount: 1 3062 { lat: 110, common_pid: 2302 } hitcount: 1 3063 3064 Totals: 3065 Hits: 89565 3066 Entries: 158 3067 Dropped: 0 3068 3069This doesn't tell us any information about how late cyclictest may have 3070woken up, but it does show us a nice histogram of how long it took from 3071the time that cyclictest was woken to the time it made it into user space. 3072