[PATCH v7 09/10] tracing: Add 'hist' trigger Documentation
From: Tom Zanussi
Date: Mon Jun 08 2015 - 17:34:53 EST
Add documentation and usage examples for 'hist' triggers.
Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
---
Documentation/trace/events.txt | 1131 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 1131 insertions(+)
diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt
index 75d25a1..fb55ac3 100644
--- a/Documentation/trace/events.txt
+++ b/Documentation/trace/events.txt
@@ -494,3 +494,1134 @@ The following commands are supported:
Note that there can be only one traceon or traceoff trigger per
triggering event.
+
+- hist
+
+ This command aggregates event hits into a hash table keyed on one or
+ more trace event format fields (or stacktrace) and a set of running
+ totals derived from one or more trace event format fields and/or
+ event counts (hitcount).
+
+ The format of a hist trigger is as follows:
+
+ hist:keys=<field1>[,field2,...][:values=<field1>[,field2,...]]
+ [:sort=field1,field2,...][:size=#entries][:pause][:continue]
+ [:clear] [if <filter>]
+
+ When a matching event is hit, an entry is added to a hash table
+ using the key(s) and value(s) named. Keys and values correspond to
+ fields in the event's format description. Values must correspond to
+ numeric fields - on an event hit, the value(s) will be added to a
+ sum kept for that field. The special string 'hitcount' can be used
+ in place of an explicit value field - this is simply a count of
+ event hits. If 'values' isn't specified, an implicit 'hitcount'
+ value will be automatically created and used as the only value.
+ Keys can be any field, or the special string 'stacktrace', which
+ will use the event's kernel stacktrace as the key. The keywords
+ 'keys' or 'key' can be used to specify keys, and the keywords
+ 'values', 'vals', or 'val' can be used to specify values. Compound
+ keys consisting of up to two fields can be specified by the 'keys'
+ keyword. Hashing a compound key produces a unique entry in the
+ table for each unique combination of component keys, and can be
+ useful for providing more fine-grained summaries of event data.
+ Additionally, sort keys consisting of up to two fields can be
+ specified by the 'sort' keyword. If more than one field is
+ specified, the result will be a 'sort within a sort': the first key
+ is taken to be the primary sort key and the second the secondary
+ key.
+
+ 'hist' triggers add a 'hist' file to each event's subdirectory.
+ Reading the 'hist' file for the event will dump the hash table in
+ its entirety to stdout. Each printed hash table entry is a simple
+ list of the keys and values comprising the entry; keys are printed
+ first and are delineated by curly braces, and are followed by the
+ set of value fields for the entry. By default, numeric fields are
+ displayed as base-10 integers. This can be modified by appending
+ any of the following modifiers to the field name:
+
+ .hex display a number as a hex value
+ .sym display an address as a symbol
+ .sym-offset display an address as a symbol and offset
+ .syscall display a syscall id as a system call name
+ .execname display a common_pid as a program name
+
+ A typical usage scenario would be the following to enable a hist
+ trigger, read its current contents, and then turn it off:
+
+ # echo 'hist:keys=skbaddr.hex:vals=len' > \
+ /sys/kernel/debug/tracing/events/net/netif_rx/trigger
+
+ # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
+
+ # echo '!hist:keys=skbaddr.hex:vals=len' > \
+ /sys/kernel/debug/tracing/events/net/netif_rx/trigger
+
+ The trigger file itself can be read to show the details of the
+ currently attached hist trigger. This information is also displayed
+ at the top of the 'hist' file when read.
+
+ By default, the size of the hash table is 2048 entries. The 'size'
+ param can be used to specify more or fewer than that. The units are
+ in terms of hashtable entries - if a run uses more entries than
+ specified, the results will show the number of 'drops', the number
+ of hits that were ignored. The size should be a power of 2 between
+ 128 and 131072 (any non- power-of-2 number specified will be rounded
+ up).
+
+ The 'sort' param can be used to specify a value field to sort on.
+ The default if unspecified is 'hitcount' and the default sort order
+ is 'ascending'. To sort in the opposite direction, append
+ .descending' to the sort key.
+
+ The 'pause' param can be used to pause an existing hist trigger or
+ to start a hist trigger but not log any events until told to do so.
+ 'continue' or 'cont' can be used to start or restart a paused hist
+ trigger.
+
+ The 'clear' param will clear the contents of a running hist trigger
+ and leave its current paused/active state.
+
+- enable_hist/disable_hist
+
+ The enable_hist and disable_hist triggers can be used to have one
+ event conditionally start and stop another event's already-attached
+ hist trigger. Any number of enable_hist and disable_hist triggers
+ can be attached to a given event, allowing that event to kick off
+ and stop aggregations on a host of other events.
+
+ The format is very similar to the enable/disable_event triggers:
+
+ enable_hist:<system>:<event>[:count]
+ disable_hist:<system>:<event>[:count]
+
+ Instead of enabling or disabling the tracing of the target event
+ into the trace buffer as the enable/disable_event triggers do, the
+ enable/disable_hist triggers enable or disable the aggregation of
+ the target event into a hash table.
+
+ A typical usage scenario for the enable_hist/disable_hist triggers
+ would be to first set up a paused hist trigger on some event,
+ followed by an enable_hist/disable_hist pair that turns the hist
+ aggregation on and off when conditions of interest are hit:
+
+ # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+ # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+
+ # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+
+ The above sets up an initially paused hist trigger which is unpaused
+ and starts aggregating events when a given program is executed, and
+ which stops aggregating when the process exits and the hist trigger
+ is paused again.
+
+ The examples below provide a more concrete illustration of the
+ concepts and typical usage patterns discussed above.
+
+
+6.2 'hist' trigger examples
+---------------------------
+
+ The first set of examples creates aggregations using the kmalloc
+ event. The fields that can be used for the hist trigger are listed
+ in the kmalloc event's format file:
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/format
+ name: kmalloc
+ ID: 374
+ format:
+ field:unsigned short common_type; offset:0; size:2; signed:0;
+ field:unsigned char common_flags; offset:2; size:1; signed:0;
+ field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
+ field:int common_pid; offset:4; size:4; signed:1;
+
+ field:unsigned long call_site; offset:8; size:8; signed:0;
+ field:const void * ptr; offset:16; size:8; signed:0;
+ field:size_t bytes_req; offset:24; size:8; signed:0;
+ field:size_t bytes_alloc; offset:32; size:8; signed:0;
+ field:gfp_t gfp_flags; offset:40; size:4; signed:0;
+
+ We'll start by creating a hist trigger that generates a simple table
+ that lists the total number of bytes requested for each function in
+ the kernel that made one or more calls to kmalloc:
+
+ # echo 'hist:key=call_site:val=bytes_req' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ This tells the tracing system to create a 'hist' trigger using the
+ call_site field of the kmalloc event as the key for the table, which
+ just means that each unique call_site address will have an entry
+ created for it in the table. The 'val=bytes_req' parameter tells
+ the hist trigger that for each unique entry (call_site) in the
+ table, it should keep a running total of the number of bytes
+ requested by that call_site.
+
+ We'll let it run for awhile and then dump the contents of the 'hist'
+ file in the kmalloc event's subdirectory (for readability, a number
+ of entries have been omitted):
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+ { call_site: 18446744072106379007 } hitcount: 1 bytes_req: 176
+ { call_site: 18446744071579557049 } hitcount: 1 bytes_req: 1024
+ { call_site: 18446744071580608289 } hitcount: 1 bytes_req: 16384
+ { call_site: 18446744071581827654 } hitcount: 1 bytes_req: 24
+ { call_site: 18446744071580700980 } hitcount: 1 bytes_req: 8
+ { call_site: 18446744071579359876 } hitcount: 1 bytes_req: 152
+ { call_site: 18446744071580795365 } hitcount: 3 bytes_req: 144
+ { call_site: 18446744071581303129 } hitcount: 3 bytes_req: 144
+ { call_site: 18446744071580713234 } hitcount: 4 bytes_req: 2560
+ { call_site: 18446744071580933750 } hitcount: 4 bytes_req: 736
+ .
+ .
+ .
+ { call_site: 18446744072106047046 } hitcount: 69 bytes_req: 5576
+ { call_site: 18446744071582116407 } hitcount: 73 bytes_req: 2336
+ { call_site: 18446744072106054684 } hitcount: 136 bytes_req: 140504
+ { call_site: 18446744072106224230 } hitcount: 136 bytes_req: 19584
+ { call_site: 18446744072106078074 } hitcount: 153 bytes_req: 2448
+ { call_site: 18446744072106062406 } hitcount: 153 bytes_req: 36720
+ { call_site: 18446744071582507929 } hitcount: 153 bytes_req: 37088
+ { call_site: 18446744072102520590 } hitcount: 273 bytes_req: 10920
+ { call_site: 18446744071582143559 } hitcount: 358 bytes_req: 716
+ { call_site: 18446744072106465852 } hitcount: 417 bytes_req: 56712
+ { call_site: 18446744072102523378 } hitcount: 485 bytes_req: 27160
+ { call_site: 18446744072099568646 } hitcount: 1676 bytes_req: 33520
+
+ Totals:
+ Hits: 4610
+ Entries: 45
+ Dropped: 0
+
+ The output displays a line for each entry, beginning with the key
+ specified in the trigger, followed by the value(s) also specified in
+ the trigger. At the beginning of the output is a line that displays
+ the trigger info, which can also be displayed by reading the
+ 'trigger' file:
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+ hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+ At the end of the output are a few lines that display the overall
+ totals for the run. The 'Hits' field shows the total number of
+ times the event trigger was hit, the 'Entries' fields shows the
+ total number of used entries in the hash table, and the 'Dropped'
+ field shows the number of hits that were dropped because the number
+ of used entries for the run exceeded the maximum number of entries
+ allowed for the table (normally 0, but if not a hint that you may
+ want to increase the size of the table using the 'size' param).
+
+ Notice in the above output that there's an extra field, 'hitcount',
+ that wasn't specified in the trigger. Also notice that in the
+ trigger info a param,'sort=hitcount', which wasn't specified in the
+ trigger either. The reason is that every trigger implicitly keeps a
+ count of the total number of hits attributed to a given entry,
+ called the 'hitcount', and that in the absence of a user-specified
+ sort param, the hitcount is used as the default sort field.
+
+ The value 'hitcount' can be used in place of an explicit value in
+ the 'values' param if you don't really need to have any particular
+ field summed and are mainly interested in hit frequencies.
+
+ To turn the hist trigger off, simply call up the trigger in command
+ history and re-execute it with a '!' prepended:
+
+ # echo '!hist:key=call_site:val=bytes_req' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ Finally, notice that the call_site as displayed in the output above
+ isn't really very useful. It's an address, but normally addresses
+ are displayed in hex. To have a numeric field displayed as hex
+ values, simply append '.hex' to the field name in the trigger:
+
+ # echo 'hist:key=call_site.hex:val=bytes_req' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site.hex:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+ { call_site: ffffffffa026b291 } hitcount: 1 bytes_req: 433
+ { call_site: ffffffffa07186ff } hitcount: 1 bytes_req: 176
+ { call_site: ffffffff811ae721 } hitcount: 1 bytes_req: 16384
+ { call_site: ffffffff811c5134 } hitcount: 1 bytes_req: 8
+ { call_site: ffffffffa04a9ebb } hitcount: 1 bytes_req: 511
+ { call_site: ffffffff8122e0a6 } hitcount: 1 bytes_req: 12
+ { call_site: ffffffff8107da84 } hitcount: 1 bytes_req: 152
+ { call_site: ffffffff812d8246 } hitcount: 1 bytes_req: 24
+ { call_site: ffffffff811dc1e5 } hitcount: 3 bytes_req: 144
+ { call_site: ffffffffa02515e8 } hitcount: 3 bytes_req: 648
+ { call_site: ffffffff81258159 } hitcount: 3 bytes_req: 144
+ { call_site: ffffffff811c80f4 } hitcount: 4 bytes_req: 544
+ .
+ .
+ .
+ { call_site: ffffffffa06c7646 } hitcount: 106 bytes_req: 8024
+ { call_site: ffffffffa06cb246 } hitcount: 132 bytes_req: 31680
+ { call_site: ffffffffa06cef7a } hitcount: 132 bytes_req: 2112
+ { call_site: ffffffff8137e399 } hitcount: 132 bytes_req: 23232
+ { call_site: ffffffffa06c941c } hitcount: 185 bytes_req: 171360
+ { call_site: ffffffffa06f2a66 } hitcount: 185 bytes_req: 26640
+ { call_site: ffffffffa036a70e } hitcount: 265 bytes_req: 10600
+ { call_site: ffffffff81325447 } hitcount: 292 bytes_req: 584
+ { call_site: ffffffffa072da3c } hitcount: 446 bytes_req: 60656
+ { call_site: ffffffffa036b1f2 } hitcount: 526 bytes_req: 29456
+ { call_site: ffffffffa0099c06 } hitcount: 1780 bytes_req: 35600
+
+ Totals:
+ Hits: 4775
+ Entries: 46
+ Dropped: 0
+
+ Even that's only marginally more useful - while hex values do look
+ more like addresses, what users are typically more interested in
+ when looking at text addresses are the corresponding symbols
+ instead. To have an address displayed as symbolic value instead,
+ simply append '.sym' or '.sym-offset' to the field name in the
+ trigger:
+
+ # echo 'hist:key=call_site.sym:val=bytes_req' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+ { call_site: [ffffffff810adcb9] syslog_print_all } hitcount: 1 bytes_req: 1024
+ { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
+ { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
+ { call_site: [ffffffff8154acbe] usb_alloc_urb } hitcount: 1 bytes_req: 192
+ { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
+ { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
+ { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
+ { call_site: [ffffffff811febd5] fsnotify_alloc_group } hitcount: 2 bytes_req: 528
+ { call_site: [ffffffff81440f58] __tty_buffer_request_room } hitcount: 2 bytes_req: 2624
+ { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 2 bytes_req: 96
+ { call_site: [ffffffffa05e19af] ieee80211_start_tx_ba_session [mac80211] } hitcount: 2 bytes_req: 464
+ { call_site: [ffffffff81672406] tcp_get_metrics } hitcount: 2 bytes_req: 304
+ { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
+ { call_site: [ffffffff81089b05] sched_create_group } hitcount: 2 bytes_req: 1424
+ .
+ .
+ .
+ { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1185 bytes_req: 123240
+ { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 1185 bytes_req: 104280
+ { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 1402 bytes_req: 190672
+ { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 1518 bytes_req: 146208
+ { call_site: [ffffffffa029070e] drm_vma_node_allow [drm] } hitcount: 1746 bytes_req: 69840
+ { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 2021 bytes_req: 792312
+ { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 2592 bytes_req: 145152
+ { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2629 bytes_req: 378576
+ { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2629 bytes_req: 3783248
+ { call_site: [ffffffff81325607] apparmor_file_alloc_security } hitcount: 5192 bytes_req: 10384
+ { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 5529 bytes_req: 110584
+ { call_site: [ffffffff8131ebf7] aa_alloc_task_context } hitcount: 21943 bytes_req: 702176
+ { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 55759 bytes_req: 5074265
+
+ Totals:
+ Hits: 109928
+ Entries: 71
+ Dropped: 0
+
+ Because the default sort key above is 'hitcount', the above shows a
+ the list of call_sites by increasing hitcount, so that at the bottom
+ we see the functions that made the most kmalloc calls during the
+ run. If instead we we wanted to see the top kmalloc callers in
+ terms of the number of bytes requested rather than the number of
+ calls, and we wanted the top caller to appear at the top, we can use
+ the 'sort' param, along with the 'descending' modifier:
+
+ # echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
+
+ { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2186 bytes_req: 3397464
+ { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1790 bytes_req: 712176
+ { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 8132 bytes_req: 513135
+ { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 106 bytes_req: 440128
+ { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2186 bytes_req: 314784
+ { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 2174 bytes_req: 208992
+ { call_site: [ffffffff811ae8e1] __kmalloc } hitcount: 8 bytes_req: 131072
+ { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 859 bytes_req: 116824
+ { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 1834 bytes_req: 102704
+ { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 972 bytes_req: 101088
+ { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 972 bytes_req: 85536
+ { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 3333 bytes_req: 66664
+ { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 209 bytes_req: 61632
+ .
+ .
+ .
+ { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
+ { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
+ { call_site: [ffffffff812d8406] copy_semundo } hitcount: 2 bytes_req: 48
+ { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 1 bytes_req: 48
+ { call_site: [ffffffffa027121a] drm_getmagic [drm] } hitcount: 1 bytes_req: 48
+ { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
+ { call_site: [ffffffff811c52f4] bprm_change_interp } hitcount: 2 bytes_req: 16
+ { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
+ { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
+ { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
+
+ Totals:
+ Hits: 32133
+ Entries: 81
+ Dropped: 0
+
+ To display the offset and size information in addition to the symbol
+ name, just use 'sym-offset' instead:
+
+ # echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site.sym-offset:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
+
+ { call_site: [ffffffffa046041c] i915_gem_execbuffer2+0x6c/0x2c0 [i915] } hitcount: 4569 bytes_req: 3163720
+ { call_site: [ffffffffa0489a66] intel_ring_begin+0xc6/0x1f0 [i915] } hitcount: 4569 bytes_req: 657936
+ { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23+0x694/0x1020 [i915] } hitcount: 1519 bytes_req: 472936
+ { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23+0x516/0x1020 [i915] } hitcount: 3050 bytes_req: 211832
+ { call_site: [ffffffff811e2a1b] seq_buf_alloc+0x1b/0x50 } hitcount: 34 bytes_req: 148384
+ { call_site: [ffffffffa04a580c] intel_crtc_page_flip+0xbc/0x870 [i915] } hitcount: 1385 bytes_req: 144040
+ { call_site: [ffffffff811ae8e1] __kmalloc+0x191/0x1b0 } hitcount: 8 bytes_req: 131072
+ { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl+0x282/0x360 [drm] } hitcount: 1385 bytes_req: 121880
+ { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc+0x32/0x100 [drm] } hitcount: 1848 bytes_req: 103488
+ { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state+0x2c/0xa0 [i915] } hitcount: 461 bytes_req: 62696
+ { call_site: [ffffffffa029070e] drm_vma_node_allow+0x2e/0xd0 [drm] } hitcount: 1541 bytes_req: 61640
+ { call_site: [ffffffff815f8d7b] sk_prot_alloc+0xcb/0x1b0 } hitcount: 57 bytes_req: 57456
+ .
+ .
+ .
+ { call_site: [ffffffff8109524a] alloc_fair_sched_group+0x5a/0x1a0 } hitcount: 2 bytes_req: 128
+ { call_site: [ffffffffa027b921] drm_vm_open_locked+0x31/0xa0 [drm] } hitcount: 3 bytes_req: 96
+ { call_site: [ffffffff8122e266] proc_self_follow_link+0x76/0xb0 } hitcount: 8 bytes_req: 96
+ { call_site: [ffffffff81213e80] load_elf_binary+0x240/0x1650 } hitcount: 3 bytes_req: 84
+ { call_site: [ffffffff8154bc62] usb_control_msg+0x42/0x110 } hitcount: 1 bytes_req: 8
+ { call_site: [ffffffffa00bf6fe] hidraw_send_report+0x7e/0x1a0 [hid] } hitcount: 1 bytes_req: 7
+ { call_site: [ffffffffa00bf1ca] hidraw_report_event+0x8a/0x120 [hid] } hitcount: 1 bytes_req: 7
+
+ Totals:
+ Hits: 26098
+ Entries: 64
+ Dropped: 0
+
+ We can also add multiple fields to the 'values' param. For example,
+ we might want to see the total number of bytes allocated alongside
+ bytes requested, and display the result sorted by bytes allocated in
+ a descending order:
+
+ # echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site.sym:vals=bytes_req,bytes_alloc:sort=bytes_alloc.descending:size=2048 [active]
+
+ { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 7403 bytes_req: 4084360 bytes_alloc: 5958016
+ { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 541 bytes_req: 2213968 bytes_alloc: 2228224
+ { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 7404 bytes_req: 1066176 bytes_alloc: 1421568
+ { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1565 bytes_req: 557368 bytes_alloc: 1037760
+ { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 9557 bytes_req: 595778 bytes_alloc: 695744
+ { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 5839 bytes_req: 430680 bytes_alloc: 470400
+ { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 2388 bytes_req: 324768 bytes_alloc: 458496
+ { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 3911 bytes_req: 219016 bytes_alloc: 250304
+ { call_site: [ffffffff815f8d7b] sk_prot_alloc } hitcount: 235 bytes_req: 236880 bytes_alloc: 240640
+ { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 557 bytes_req: 169024 bytes_alloc: 221760
+ { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 9378 bytes_req: 187548 bytes_alloc: 206312
+ { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1519 bytes_req: 157976 bytes_alloc: 194432
+ .
+ .
+ .
+ { call_site: [ffffffff8109bd3b] sched_autogroup_create_attach } hitcount: 2 bytes_req: 144 bytes_alloc: 192
+ { call_site: [ffffffff81097ee8] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
+ { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
+ { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
+ { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
+ { call_site: [ffffffff81213e80] load_elf_binary } hitcount: 3 bytes_req: 84 bytes_alloc: 96
+ { call_site: [ffffffff81079a2e] kthread_create_on_node } hitcount: 1 bytes_req: 56 bytes_alloc: 64
+ { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
+ { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 bytes_alloc: 8
+ { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
+
+ Totals:
+ Hits: 66598
+ Entries: 65
+ Dropped: 0
+
+ Finally, to finish off our kmalloc example, instead of simply having
+ the hist trigger display symbolic call_sites, we can have the hist
+ trigger additionally display the complete set of kernel stack traces
+ that led to each call_sites. To do that, we simply use the special
+ value 'stacktrace' for the key param:
+
+ # echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ The above trigger will use the kernel stack trace in effect when an
+ event is triggered as the key for the hash table. This allows the
+ enumeration of every kernel callpath that led up to a particular
+ event, along with a running total of any of the event fields for
+ that event. Here we tally bytes requested and bytes allocated for
+ every callpath in the system that led up to a kmalloc (in this case
+ every callpath to a kmalloc for a kernel compile):
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active]
+
+ { stacktrace:
+ __kmalloc_track_caller+0x10b/0x1a0
+ kmemdup+0x20/0x50
+ hidraw_report_event+0x8a/0x120 [hid]
+ hid_report_raw_event+0x3ea/0x440 [hid]
+ hid_input_report+0x112/0x190 [hid]
+ hid_irq_in+0xc2/0x260 [usbhid]
+ __usb_hcd_giveback_urb+0x72/0x120
+ usb_giveback_urb_bh+0x9e/0xe0
+ tasklet_hi_action+0xf8/0x100
+ __do_softirq+0x114/0x2c0
+ irq_exit+0xa5/0xb0
+ do_IRQ+0x5a/0xf0
+ ret_from_intr+0x0/0x30
+ cpuidle_enter+0x17/0x20
+ cpu_startup_entry+0x315/0x3e0
+ rest_init+0x7c/0x80
+ } hitcount: 3 bytes_req: 21 bytes_alloc: 24
+ { stacktrace:
+ __kmalloc_track_caller+0x10b/0x1a0
+ kmemdup+0x20/0x50
+ hidraw_report_event+0x8a/0x120 [hid]
+ hid_report_raw_event+0x3ea/0x440 [hid]
+ hid_input_report+0x112/0x190 [hid]
+ hid_irq_in+0xc2/0x260 [usbhid]
+ __usb_hcd_giveback_urb+0x72/0x120
+ usb_giveback_urb_bh+0x9e/0xe0
+ tasklet_hi_action+0xf8/0x100
+ __do_softirq+0x114/0x2c0
+ irq_exit+0xa5/0xb0
+ do_IRQ+0x5a/0xf0
+ ret_from_intr+0x0/0x30
+ } hitcount: 3 bytes_req: 21 bytes_alloc: 24
+ { stacktrace:
+ kmem_cache_alloc_trace+0xeb/0x150
+ aa_alloc_task_context+0x27/0x40
+ apparmor_cred_prepare+0x1f/0x50
+ security_prepare_creds+0x16/0x20
+ prepare_creds+0xdf/0x1a0
+ SyS_capset+0xb5/0x200
+ system_call_fastpath+0x12/0x6a
+ } hitcount: 1 bytes_req: 32 bytes_alloc: 32
+ .
+ .
+ .
+ { stacktrace:
+ __kmalloc+0x11b/0x1b0
+ i915_gem_execbuffer2+0x6c/0x2c0 [i915]
+ drm_ioctl+0x349/0x670 [drm]
+ do_vfs_ioctl+0x2f0/0x4f0
+ SyS_ioctl+0x81/0xa0
+ system_call_fastpath+0x12/0x6a
+ } hitcount: 17726 bytes_req: 13944120 bytes_alloc: 19593808
+ { stacktrace:
+ __kmalloc+0x11b/0x1b0
+ load_elf_phdrs+0x76/0xa0
+ load_elf_binary+0x102/0x1650
+ search_binary_handler+0x97/0x1d0
+ do_execveat_common.isra.34+0x551/0x6e0
+ SyS_execve+0x3a/0x50
+ return_from_execve+0x0/0x23
+ } hitcount: 33348 bytes_req: 17152128 bytes_alloc: 20226048
+ { stacktrace:
+ kmem_cache_alloc_trace+0xeb/0x150
+ apparmor_file_alloc_security+0x27/0x40
+ security_file_alloc+0x16/0x20
+ get_empty_filp+0x93/0x1c0
+ path_openat+0x31/0x5f0
+ do_filp_open+0x3a/0x90
+ do_sys_open+0x128/0x220
+ SyS_open+0x1e/0x20
+ system_call_fastpath+0x12/0x6a
+ } hitcount: 4766422 bytes_req: 9532844 bytes_alloc: 38131376
+ { stacktrace:
+ __kmalloc+0x11b/0x1b0
+ seq_buf_alloc+0x1b/0x50
+ seq_read+0x2cc/0x370
+ proc_reg_read+0x3d/0x80
+ __vfs_read+0x28/0xe0
+ vfs_read+0x86/0x140
+ SyS_read+0x46/0xb0
+ system_call_fastpath+0x12/0x6a
+ } hitcount: 19133 bytes_req: 78368768 bytes_alloc: 78368768
+
+ Totals:
+ Hits: 6085872
+ Entries: 253
+ Dropped: 0
+
+ If you key a hist trigger on common_pid, in order for example to
+ gather and display sorted totals for each process, you can use the
+ special .execname modifier to display the executable names for the
+ processes in the table rather than raw pids. The example below
+ keeps a per-process sum of total bytes read:
+
+ # echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \
+ /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
+
+ # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/hist
+ # trigger info: hist:keys=common_pid.execname:vals=count:sort=count.descending:size=2048 [active]
+
+ { common_pid: gnome-terminal [ 3196] } hitcount: 280 count: 1093512
+ { common_pid: Xorg [ 1309] } hitcount: 525 count: 256640
+ { common_pid: compiz [ 2889] } hitcount: 59 count: 254400
+ { common_pid: bash [ 8710] } hitcount: 3 count: 66369
+ { common_pid: dbus-daemon-lau [ 8703] } hitcount: 49 count: 47739
+ { common_pid: irqbalance [ 1252] } hitcount: 27 count: 27648
+ { common_pid: 01ifupdown [ 8705] } hitcount: 3 count: 17216
+ { common_pid: dbus-daemon [ 772] } hitcount: 10 count: 12396
+ { common_pid: Socket Thread [ 8342] } hitcount: 11 count: 11264
+ { common_pid: nm-dhcp-client. [ 8701] } hitcount: 6 count: 7424
+ { common_pid: gmain [ 1315] } hitcount: 18 count: 6336
+ .
+ .
+ .
+ { common_pid: postgres [ 1892] } hitcount: 2 count: 32
+ { common_pid: postgres [ 1891] } hitcount: 2 count: 32
+ { common_pid: gmain [ 8704] } hitcount: 2 count: 32
+ { common_pid: upstart-dbus-br [ 2740] } hitcount: 21 count: 21
+ { common_pid: nm-dispatcher.a [ 8696] } hitcount: 1 count: 16
+ { common_pid: indicator-datet [ 2904] } hitcount: 1 count: 16
+ { common_pid: gdbus [ 2998] } hitcount: 1 count: 16
+ { common_pid: rtkit-daemon [ 2052] } hitcount: 1 count: 8
+ { common_pid: init [ 1] } hitcount: 2 count: 2
+
+ Totals:
+ Hits: 2116
+ Entries: 51
+ Dropped: 0
+
+ Similarly, if you key a hist trigger on syscall id, for example to
+ gather and display a list of systemwide syscall hits, you can use
+ the special .syscall modifier to display the syscall names rather
+ than raw ids. The example below keeps a running total of syscall
+ counts for the system during the run:
+
+ # echo 'hist:key=id.syscall:val=hitcount' > \
+ /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
+
+ # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
+ # trigger info: hist:keys=id.syscall:vals=hitcount:sort=hitcount:size=2048 [active]
+
+ { id: sys_fsync [ 74] } hitcount: 1
+ { id: sys_newuname [ 63] } hitcount: 1
+ { id: sys_prctl [157] } hitcount: 1
+ { id: sys_statfs [137] } hitcount: 1
+ { id: sys_symlink [ 88] } hitcount: 1
+ { id: sys_sendmmsg [307] } hitcount: 1
+ { id: sys_semctl [ 66] } hitcount: 1
+ { id: sys_readlink [ 89] } hitcount: 3
+ { id: sys_bind [ 49] } hitcount: 3
+ { id: sys_getsockname [ 51] } hitcount: 3
+ { id: sys_unlink [ 87] } hitcount: 3
+ { id: sys_rename [ 82] } hitcount: 4
+ { id: unknown_syscall [ 58] } hitcount: 4
+ { id: sys_connect [ 42] } hitcount: 4
+ { id: sys_getpid [ 39] } hitcount: 4
+ .
+ .
+ .
+ { id: sys_rt_sigprocmask [ 14] } hitcount: 952
+ { id: sys_futex [202] } hitcount: 1534
+ { id: sys_write [ 1] } hitcount: 2689
+ { id: sys_setitimer [ 38] } hitcount: 2797
+ { id: sys_read [ 0] } hitcount: 3202
+ { id: sys_select [ 23] } hitcount: 3773
+ { id: sys_writev [ 20] } hitcount: 4531
+ { id: sys_poll [ 7] } hitcount: 8314
+ { id: sys_recvmsg [ 47] } hitcount: 13738
+ { id: sys_ioctl [ 16] } hitcount: 21843
+
+ Totals:
+ Hits: 67612
+ Entries: 72
+ Dropped: 0
+
+ The syscall counts above provide a rough overall picture of system
+ call activity on the system; we can see for example that the most
+ popular system call on this system was the 'sys_ioctl' system call.
+
+ We can use 'compound' keys to refine that number and provide some
+ further insight as to which processes exactly contribute to the
+ overall ioctl count.
+
+ The command below keeps a hitcount for every unique combination of
+ system call id and pid - the end result is essentially a table
+ that keeps a per-pid sum of system call hits. The results are
+ sorted using the system call id as the primary key, and the
+ hitcount sum as the secondary key:
+
+ # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \
+ /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
+
+ # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
+ # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active]
+
+ { id: sys_read [ 0], common_pid: rtkit-daemon [ 1877] } hitcount: 1
+ { id: sys_read [ 0], common_pid: gdbus [ 2976] } hitcount: 1
+ { id: sys_read [ 0], common_pid: console-kit-dae [ 3400] } hitcount: 1
+ { id: sys_read [ 0], common_pid: postgres [ 1865] } hitcount: 1
+ { id: sys_read [ 0], common_pid: deja-dup-monito [ 3543] } hitcount: 2
+ { id: sys_read [ 0], common_pid: NetworkManager [ 890] } hitcount: 2
+ { id: sys_read [ 0], common_pid: evolution-calen [ 3048] } hitcount: 2
+ { id: sys_read [ 0], common_pid: postgres [ 1864] } hitcount: 2
+ { id: sys_read [ 0], common_pid: nm-applet [ 3022] } hitcount: 2
+ { id: sys_read [ 0], common_pid: whoopsie [ 1212] } hitcount: 2
+ .
+ .
+ .
+ { id: sys_ioctl [ 16], common_pid: bash [ 8479] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: bash [ 3472] } hitcount: 12
+ { id: sys_ioctl [ 16], common_pid: gnome-terminal [ 3199] } hitcount: 16
+ { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 1808
+ { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 5580
+ .
+ .
+ .
+ { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2690] } hitcount: 3
+ { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2688] } hitcount: 16
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 975] } hitcount: 2
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 3204] } hitcount: 4
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 2888] } hitcount: 4
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 3003] } hitcount: 4
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 2873] } hitcount: 4
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 3196] } hitcount: 6
+ { id: sys_openat [257], common_pid: java [ 2623] } hitcount: 2
+ { id: sys_eventfd2 [290], common_pid: ibus-ui-gtk3 [ 2760] } hitcount: 4
+ { id: sys_eventfd2 [290], common_pid: compiz [ 2994] } hitcount: 6
+
+ Totals:
+ Hits: 31536
+ Entries: 323
+ Dropped: 0
+
+ The above list does give us a breakdown of the ioctl syscall by
+ pid, but it also gives us quite a bit more than that, which we
+ don't really care about at the moment. Since we know the syscall
+ id for sys_ioctl (16, displayed next to the sys_ioctl name), we
+ can use that to filter out all the other syscalls:
+
+ # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \
+ /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
+
+ # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
+ # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active]
+
+ { id: sys_ioctl [ 16], common_pid: gmain [ 2769] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: evolution-addre [ 8571] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: gmain [ 3003] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: gmain [ 2781] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: gmain [ 2829] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: bash [ 8726] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: bash [ 8508] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: gmain [ 2970] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: gmain [ 2768] } hitcount: 1
+ .
+ .
+ .
+ { id: sys_ioctl [ 16], common_pid: pool [ 8559] } hitcount: 45
+ { id: sys_ioctl [ 16], common_pid: pool [ 8555] } hitcount: 48
+ { id: sys_ioctl [ 16], common_pid: pool [ 8551] } hitcount: 48
+ { id: sys_ioctl [ 16], common_pid: avahi-daemon [ 896] } hitcount: 66
+ { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 26674
+ { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 73443
+
+ Totals:
+ Hits: 101162
+ Entries: 103
+ Dropped: 0
+
+ The above output shows that 'compiz' and 'Xorg' are far and away
+ the heaviest ioctl callers (do the really need to do so much of
+ that?).
+
+ The compound key examples used a key and a sum value (hitcount) to
+ sort the output, but we can just as easily use two keys instead.
+ Here's an example where we use a compound key composed of the the
+ common_pid and size event fields. Sorting with pid as the primary
+ key and 'size' as the secondary key allows us to display an
+ ordered summary of the recvfrom sizes, with counts, received by
+ each process:
+
+ # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \
+ /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger
+
+ # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist
+ # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active]
+
+ { common_pid: smbd [ 784], size: 4 } hitcount: 1
+ { common_pid: dnsmasq [ 1412], size: 4096 } hitcount: 672
+ { common_pid: postgres [ 1796], size: 1000 } hitcount: 6
+ { common_pid: postgres [ 1867], size: 1000 } hitcount: 10
+ { common_pid: bamfdaemon [ 2787], size: 28 } hitcount: 2
+ { common_pid: bamfdaemon [ 2787], size: 14360 } hitcount: 1
+ { common_pid: compiz [ 2994], size: 8 } hitcount: 1
+ { common_pid: compiz [ 2994], size: 20 } hitcount: 11
+ { common_pid: gnome-terminal [ 3199], size: 4 } hitcount: 2
+ { common_pid: firefox [ 8817], size: 4 } hitcount: 1
+ { common_pid: firefox [ 8817], size: 8 } hitcount: 5
+ { common_pid: firefox [ 8817], size: 588 } hitcount: 2
+ { common_pid: firefox [ 8817], size: 628 } hitcount: 1
+ { common_pid: firefox [ 8817], size: 6944 } hitcount: 1
+ { common_pid: firefox [ 8817], size: 408880 } hitcount: 2
+ { common_pid: firefox [ 8822], size: 8 } hitcount: 2
+ { common_pid: firefox [ 8822], size: 160 } hitcount: 2
+ { common_pid: firefox [ 8822], size: 320 } hitcount: 2
+ { common_pid: firefox [ 8822], size: 352 } hitcount: 1
+ .
+ .
+ .
+ { common_pid: pool [ 8923], size: 1960 } hitcount: 10
+ { common_pid: pool [ 8923], size: 2048 } hitcount: 10
+ { common_pid: pool [ 8924], size: 1960 } hitcount: 10
+ { common_pid: pool [ 8924], size: 2048 } hitcount: 10
+ { common_pid: pool [ 8928], size: 1964 } hitcount: 4
+ { common_pid: pool [ 8928], size: 1965 } hitcount: 2
+ { common_pid: pool [ 8928], size: 2048 } hitcount: 6
+ { common_pid: pool [ 8929], size: 1982 } hitcount: 1
+ { common_pid: pool [ 8929], size: 2048 } hitcount: 1
+
+ Totals:
+ Hits: 2016
+ Entries: 224
+ Dropped: 0
+
+ The above example also illustrates the fact that although a compound
+ key is treated as a single entity for hashing purposes, the sub-keys
+ it's composed of can be accessed independently.
+
+ The next example uses a string field as the hash key and
+ demonstrates how you can manually pause and continue a hist trigger.
+ In this example, we'll aggregate fork counts and don't expect a
+ large number of entries in the hash table, so we'll drop it to a
+ much smaller number, say 256:
+
+ # echo 'hist:key=child_comm:val=hitcount:size=256' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+ # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
+
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: ibus-daemon } hitcount: 1
+ { child_comm: whoopsie } hitcount: 1
+ { child_comm: smbd } hitcount: 1
+ { child_comm: gdbus } hitcount: 1
+ { child_comm: kthreadd } hitcount: 1
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: evolution-alarm } hitcount: 2
+ { child_comm: Socket Thread } hitcount: 2
+ { child_comm: postgres } hitcount: 2
+ { child_comm: bash } hitcount: 3
+ { child_comm: compiz } hitcount: 3
+ { child_comm: evolution-sourc } hitcount: 4
+ { child_comm: dhclient } hitcount: 4
+ { child_comm: pool } hitcount: 5
+ { child_comm: nm-dispatcher.a } hitcount: 8
+ { child_comm: firefox } hitcount: 8
+ { child_comm: dbus-daemon } hitcount: 8
+ { child_comm: glib-pacrunner } hitcount: 10
+ { child_comm: evolution } hitcount: 23
+
+ Totals:
+ Hits: 89
+ Entries: 20
+ Dropped: 0
+
+ If we want to pause the hist trigger, we can simply append :pause to
+ the command that started the trigger. Notice that the trigger info
+ displays as [paused]:
+
+ # echo 'hist:key=child_comm:val=hitcount:size=256:pause' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+ # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [paused]
+
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: kthreadd } hitcount: 1
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: gdbus } hitcount: 1
+ { child_comm: ibus-daemon } hitcount: 1
+ { child_comm: Socket Thread } hitcount: 2
+ { child_comm: evolution-alarm } hitcount: 2
+ { child_comm: smbd } hitcount: 2
+ { child_comm: bash } hitcount: 3
+ { child_comm: whoopsie } hitcount: 3
+ { child_comm: compiz } hitcount: 3
+ { child_comm: evolution-sourc } hitcount: 4
+ { child_comm: pool } hitcount: 5
+ { child_comm: postgres } hitcount: 6
+ { child_comm: firefox } hitcount: 8
+ { child_comm: dhclient } hitcount: 10
+ { child_comm: emacs } hitcount: 12
+ { child_comm: dbus-daemon } hitcount: 20
+ { child_comm: nm-dispatcher.a } hitcount: 20
+ { child_comm: evolution } hitcount: 35
+ { child_comm: glib-pacrunner } hitcount: 59
+
+ Totals:
+ Hits: 199
+ Entries: 21
+ Dropped: 0
+
+ To manually continue having the trigger aggregate events, append
+ :cont instead. Notice that the trigger info displays as [active]
+ again, and the data has changed:
+
+ # echo 'hist:key=child_comm:val=hitcount:size=256:cont' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+ # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
+
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: kthreadd } hitcount: 1
+ { child_comm: gdbus } hitcount: 1
+ { child_comm: ibus-daemon } hitcount: 1
+ { child_comm: Socket Thread } hitcount: 2
+ { child_comm: evolution-alarm } hitcount: 2
+ { child_comm: smbd } hitcount: 2
+ { child_comm: whoopsie } hitcount: 3
+ { child_comm: compiz } hitcount: 3
+ { child_comm: evolution-sourc } hitcount: 4
+ { child_comm: bash } hitcount: 5
+ { child_comm: pool } hitcount: 5
+ { child_comm: postgres } hitcount: 6
+ { child_comm: firefox } hitcount: 8
+ { child_comm: dhclient } hitcount: 11
+ { child_comm: emacs } hitcount: 12
+ { child_comm: dbus-daemon } hitcount: 22
+ { child_comm: nm-dispatcher.a } hitcount: 22
+ { child_comm: evolution } hitcount: 35
+ { child_comm: glib-pacrunner } hitcount: 59
+
+ Totals:
+ Hits: 206
+ Entries: 21
+ Dropped: 0
+
+ The previous example showed how to start and stop a hist trigger by
+ appending 'pause' and 'continue' to the hist trigger command. A
+ hist trigger can also be started in a paused state by initially
+ starting the trigger with ':pause' appended. This allows you to
+ start the trigger only when you're ready to start collecting data
+ and not before. For example, start the trigger in a paused state,
+ then unpause it and do something you want to measure, then pause the
+ trigger when done.
+
+ Of course, doing this manually can be difficult and error-prone, but
+ it is possible to automatically start and stop a hist trigger based
+ on some condition, via the enable_hist and disable_hist triggers.
+
+ For example, suppose we wanted to take a look at the relative
+ weights in terms of skb length for each callpath that leads to a
+ netif_receieve_skb event when downloading a decent-sized file using
+ wget.
+
+ First we set up an initially paused stacktrace trigger on the
+ netif_receive_skb event:
+
+ # echo 'hist:key=stacktrace:vals=len:pause' > \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+ Next, we set up an 'enable_hist' trigger on the sched_process_exec
+ event, with an 'if filename==/usr/bin/wget' filter. The effect of
+ this new trigger is that it will 'unpause' the hist trigger we just
+ set up on netif_receive_skb if and only if it sees a
+ sched_process_exec event with a filename of '/usr/bin/wget'. When
+ that happens, all netif_receive_skb events are aggregated into a
+ hash table keyed on stacktrace:
+
+ # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+
+ The aggregation continues until the netif_receive_skb is paused
+ again, which is what the following disable_hist event does by
+ creating a similar setup on the sched_process_exit event, using the
+ filter 'comm==wget':
+
+ # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+
+ Whenever a process exits and the comm field of the disable_hist
+ trigger filter matches 'comm==wget', the netif_receive_skb hist
+ trigger is disabled.
+
+ The overall effect is that netif_received_skb events are aggregated
+ into the hash table for only the duration of the wget. Executing a
+ wget command and then listing the 'hist' file will display the
+ output generated by the wget command:
+
+ $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
+
+ # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
+ # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
+
+ { stacktrace:
+ __netif_receive_skb_core+0x46d/0x990
+ __netif_receive_skb+0x18/0x60
+ netif_receive_skb_internal+0x23/0x90
+ napi_gro_receive+0xc8/0x100
+ ieee80211_deliver_skb+0xd6/0x270 [mac80211]
+ ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
+ ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
+ ieee80211_rx+0x31d/0x900 [mac80211]
+ iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
+ iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
+ iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
+ irq_thread_fn+0x20/0x50
+ irq_thread+0x11f/0x150
+ kthread+0xd2/0xf0
+ ret_from_fork+0x42/0x70
+ } hitcount: 85 len: 28884
+ { stacktrace:
+ __netif_receive_skb_core+0x46d/0x990
+ __netif_receive_skb+0x18/0x60
+ netif_receive_skb_internal+0x23/0x90
+ napi_gro_complete+0xa4/0xe0
+ dev_gro_receive+0x23a/0x360
+ napi_gro_receive+0x30/0x100
+ ieee80211_deliver_skb+0xd6/0x270 [mac80211]
+ ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
+ ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
+ ieee80211_rx+0x31d/0x900 [mac80211]
+ iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
+ iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
+ iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
+ irq_thread_fn+0x20/0x50
+ irq_thread+0x11f/0x150
+ kthread+0xd2/0xf0
+ } hitcount: 98 len: 664329
+ { stacktrace:
+ __netif_receive_skb_core+0x46d/0x990
+ __netif_receive_skb+0x18/0x60
+ process_backlog+0xa8/0x150
+ net_rx_action+0x15d/0x340
+ __do_softirq+0x114/0x2c0
+ do_softirq_own_stack+0x1c/0x30
+ do_softirq+0x65/0x70
+ __local_bh_enable_ip+0xb5/0xc0
+ ip_finish_output+0x1f4/0x840
+ ip_output+0x6b/0xc0
+ ip_local_out_sk+0x31/0x40
+ ip_send_skb+0x1a/0x50
+ udp_send_skb+0x173/0x2a0
+ udp_sendmsg+0x2bf/0x9f0
+ inet_sendmsg+0x64/0xa0
+ sock_sendmsg+0x3d/0x50
+ } hitcount: 115 len: 13030
+ { stacktrace:
+ __netif_receive_skb_core+0x46d/0x990
+ __netif_receive_skb+0x18/0x60
+ netif_receive_skb_internal+0x23/0x90
+ napi_gro_complete+0xa4/0xe0
+ napi_gro_flush+0x6d/0x90
+ iwl_pcie_irq_handler+0x92a/0x12f0 [iwlwifi]
+ irq_thread_fn+0x20/0x50
+ irq_thread+0x11f/0x150
+ kthread+0xd2/0xf0
+ ret_from_fork+0x42/0x70
+ } hitcount: 934 len: 5512212
+
+ Totals:
+ Hits: 1232
+ Entries: 4
+ Dropped: 0
+
+ The above shows all the netif_receive_skb callpaths and their total
+ lengths for the duration of the wget command.
+
+ The 'clear' hist trigger param can be used to clear the hash table.
+ Suppose we wanted to try another run of the previous example but
+ this time also wanted to see the complete list of events that went
+ into the histogram. In order to avoid having to set everything up
+ again, we can just clear the histogram first:
+
+ # echo 'hist:key=stacktrace:vals=len:clear' > \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+ Just to verify that it is in fact cleared, here's what we now see in
+ the hist file:
+
+ # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
+ # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
+
+ Totals:
+ Hits: 0
+ Entries: 0
+ Dropped: 0
+
+ Since we want to see the detailed list of every netif_receive_skb
+ event occurring during the new run, which are in fact same events
+ being aggregated into the hash table, we add some additional
+ 'enable_event' events the triggering sched_process_exec and
+ sched_process_exit events as such:
+
+ # echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+
+ # echo 'disable_event:net:netif_receive_skb if comm==wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+
+ If you read the trigger files for the sched_process_exec and
+ sched_process_exit triggers, you should see two triggers for each:
+ one enabling/disabling the hist aggregation and the other
+ enabling/disabling the logging of events:
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+ enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
+ enable_hist:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+ enable_event:net:netif_receive_skb:unlimited if comm==wget
+ disable_hist:net:netif_receive_skb:unlimited if comm==wget
+
+ In other words, whenever either of the sched_process_exec or
+ sched_process_exit events is hit and matches 'wget', it enables or
+ disables both the histogram and the event log, and what you end up
+ with is a hash table and set of events just covering the specified
+ duration. Run the wget command again:
+
+ $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
+
+ Displaying the 'hist' file should show something similar to what you
+ saw in the last run, but this time you should also see the
+ individual events in the trace file:
+
+ # cat /sys/kernel/debug/tracing/trace
+
+ # tracer: nop
+ #
+ # entries-in-buffer/entries-written: 183/1426 #P:4
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ wget-15108 [000] ..s1 31769.606929: netif_receive_skb: dev=lo skbaddr=ffff88009c353100 len=60
+ wget-15108 [000] ..s1 31769.606999: netif_receive_skb: dev=lo skbaddr=ffff88009c353200 len=60
+ dnsmasq-1382 [000] ..s1 31769.677652: netif_receive_skb: dev=lo skbaddr=ffff88009c352b00 len=130
+ dnsmasq-1382 [000] ..s1 31769.685917: netif_receive_skb: dev=lo skbaddr=ffff88009c352200 len=138
+ ##### CPU 2 buffer started ####
+ irq/29-iwlwifi-559 [002] ..s. 31772.031529: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433d00 len=2948
+ irq/29-iwlwifi-559 [002] ..s. 31772.031572: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432200 len=1500
+ irq/29-iwlwifi-559 [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948
+ irq/29-iwlwifi-559 [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948
+ irq/29-iwlwifi-559 [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500
+ .
+ .
+ .
--
1.9.3
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