--- /dev/null
+================
+Event Histograms
+================
+
+Documentation written by Tom Zanussi
+
+1. Introduction
+===============
+
+ Histogram triggers are special event triggers that can be used to
+ aggregate trace event data into histograms. For information on
+ trace events and event triggers, see Documentation/trace/events.rst.
+
+
+2. Histogram Trigger Command
+============================
+
+ A histogram trigger command is an event trigger command that
+ aggregates event hits into a hash table keyed on one or more trace
+ event format fields (or stacktrace) and a set of running totals
+ derived from one or more trace event format fields and/or event
+ counts (hitcount).
+
+ The format of a hist trigger is as follows::
+
+ hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>]
+ [:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue]
+ [:clear][:name=histname1] [if <filter>]
+
+ When a matching event is hit, an entry is added to a hash table
+ using the key(s) and value(s) named. Keys and values correspond to
+ fields in the event's format description. Values must correspond to
+ numeric fields - on an event hit, the value(s) will be added to a
+ sum kept for that field. The special string 'hitcount' can be used
+ in place of an explicit value field - this is simply a count of
+ event hits. If 'values' isn't specified, an implicit 'hitcount'
+ value will be automatically created and used as the only value.
+ Keys can be any field, or the special string 'stacktrace', which
+ will use the event's kernel stacktrace as the key. The keywords
+ 'keys' or 'key' can be used to specify keys, and the keywords
+ 'values', 'vals', or 'val' can be used to specify values. Compound
+ keys consisting of up to two fields can be specified by the 'keys'
+ keyword. Hashing a compound key produces a unique entry in the
+ table for each unique combination of component keys, and can be
+ useful for providing more fine-grained summaries of event data.
+ Additionally, sort keys consisting of up to two fields can be
+ specified by the 'sort' keyword. If more than one field is
+ specified, the result will be a 'sort within a sort': the first key
+ is taken to be the primary sort key and the second the secondary
+ key. If a hist trigger is given a name using the 'name' parameter,
+ its histogram data will be shared with other triggers of the same
+ name, and trigger hits will update this common data. Only triggers
+ with 'compatible' fields can be combined in this way; triggers are
+ 'compatible' if the fields named in the trigger share the same
+ number and type of fields and those fields also have the same names.
+ Note that any two events always share the compatible 'hitcount' and
+ 'stacktrace' fields and can therefore be combined using those
+ fields, however pointless that may be.
+
+ 'hist' triggers add a 'hist' file to each event's subdirectory.
+ Reading the 'hist' file for the event will dump the hash table in
+ its entirety to stdout. If there are multiple hist triggers
+ attached to an event, there will be a table for each trigger in the
+ output. The table displayed for a named trigger will be the same as
+ any other instance having the same name. Each printed hash table
+ entry is a simple list of the keys and values comprising the entry;
+ keys are printed first and are delineated by curly braces, and are
+ followed by the set of value fields for the entry. By default,
+ numeric fields are displayed as base-10 integers. This can be
+ modified by appending any of the following modifiers to the field
+ name:
+
+ =========== ==========================================
+ .hex display a number as a hex value
+ .sym display an address as a symbol
+ .sym-offset display an address as a symbol and offset
+ .syscall display a syscall id as a system call name
+ .execname display a common_pid as a program name
+ .log2 display log2 value rather than raw number
+ .usecs display a common_timestamp in microseconds
+ =========== ==========================================
+
+ Note that in general the semantics of a given field aren't
+ interpreted when applying a modifier to it, but there are some
+ restrictions to be aware of in this regard:
+
+ - only the 'hex' modifier can be used for values (because values
+ are essentially sums, and the other modifiers don't make sense
+ in that context).
+ - the 'execname' modifier can only be used on a 'common_pid'. The
+ reason for this is that the execname is simply the 'comm' value
+ saved for the 'current' process when an event was triggered,
+ which is the same as the common_pid value saved by the event
+ tracing code. Trying to apply that comm value to other pid
+ values wouldn't be correct, and typically events that care save
+ pid-specific comm fields in the event itself.
+
+ A typical usage scenario would be the following to enable a hist
+ trigger, read its current contents, and then turn it off::
+
+ # echo 'hist:keys=skbaddr.hex:vals=len' > \
+ /sys/kernel/debug/tracing/events/net/netif_rx/trigger
+
+ # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
+
+ # echo '!hist:keys=skbaddr.hex:vals=len' > \
+ /sys/kernel/debug/tracing/events/net/netif_rx/trigger
+
+ The trigger file itself can be read to show the details of the
+ currently attached hist trigger. This information is also displayed
+ at the top of the 'hist' file when read.
+
+ By default, the size of the hash table is 2048 entries. The 'size'
+ parameter can be used to specify more or fewer than that. The units
+ are in terms of hashtable entries - if a run uses more entries than
+ specified, the results will show the number of 'drops', the number
+ of hits that were ignored. The size should be a power of 2 between
+ 128 and 131072 (any non- power-of-2 number specified will be rounded
+ up).
+
+ The 'sort' parameter can be used to specify a value field to sort
+ on. The default if unspecified is 'hitcount' and the default sort
+ order is 'ascending'. To sort in the opposite direction, append
+ .descending' to the sort key.
+
+ The 'pause' parameter can be used to pause an existing hist trigger
+ or to start a hist trigger but not log any events until told to do
+ so. 'continue' or 'cont' can be used to start or restart a paused
+ hist trigger.
+
+ The 'clear' parameter will clear the contents of a running hist
+ trigger and leave its current paused/active state.
+
+ Note that the 'pause', 'cont', and 'clear' parameters should be
+ applied using 'append' shell operator ('>>') if applied to an
+ existing trigger, rather than via the '>' operator, which will cause
+ the trigger to be removed through truncation.
+
+- enable_hist/disable_hist
+
+ The enable_hist and disable_hist triggers can be used to have one
+ event conditionally start and stop another event's already-attached
+ hist trigger. Any number of enable_hist and disable_hist triggers
+ can be attached to a given event, allowing that event to kick off
+ and stop aggregations on a host of other events.
+
+ The format is very similar to the enable/disable_event triggers::
+
+ enable_hist:<system>:<event>[:count]
+ disable_hist:<system>:<event>[:count]
+
+ Instead of enabling or disabling the tracing of the target event
+ into the trace buffer as the enable/disable_event triggers do, the
+ enable/disable_hist triggers enable or disable the aggregation of
+ the target event into a hash table.
+
+ A typical usage scenario for the enable_hist/disable_hist triggers
+ would be to first set up a paused hist trigger on some event,
+ followed by an enable_hist/disable_hist pair that turns the hist
+ aggregation on and off when conditions of interest are hit::
+
+ # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+ # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+
+ # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+
+ The above sets up an initially paused hist trigger which is unpaused
+ and starts aggregating events when a given program is executed, and
+ which stops aggregating when the process exits and the hist trigger
+ is paused again.
+
+ The examples below provide a more concrete illustration of the
+ concepts and typical usage patterns discussed above.
+
+'special' event fields
+------------------------
+
+ There are a number of 'special event fields' available for use as
+ keys or values in a hist trigger. These look like and behave as if
+ they were actual event fields, but aren't really part of the event's
+ field definition or format file. They are however available for any
+ event, and can be used anywhere an actual event field could be.
+ They are:
+
+ ====================== ==== =======================================
+ common_timestamp u64 timestamp (from ring buffer) associated
+ with the event, in nanoseconds. May be
+ modified by .usecs to have timestamps
+ interpreted as microseconds.
+ cpu int the cpu on which the event occurred.
+ ====================== ==== =======================================
+
+Extended error information
+--------------------------
+
+ For some error conditions encountered when invoking a hist trigger
+ command, extended error information is available via the
+ corresponding event's 'hist' file. Reading the hist file after an
+ error will display more detailed information about what went wrong,
+ if information is available. This extended error information will
+ be available until the next hist trigger command for that event.
+
+ If available for a given error condition, the extended error
+ information and usage takes the following form::
+
+ # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
+ echo: write error: Invalid argument
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/hist
+ ERROR: Couldn't yyy: zzz
+ Last command: xxx
+
+6.2 'hist' trigger examples
+---------------------------
+
+ The first set of examples creates aggregations using the kmalloc
+ event. The fields that can be used for the hist trigger are listed
+ in the kmalloc event's format file::
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/format
+ name: kmalloc
+ ID: 374
+ format:
+ field:unsigned short common_type; offset:0; size:2; signed:0;
+ field:unsigned char common_flags; offset:2; size:1; signed:0;
+ field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
+ field:int common_pid; offset:4; size:4; signed:1;
+
+ field:unsigned long call_site; offset:8; size:8; signed:0;
+ field:const void * ptr; offset:16; size:8; signed:0;
+ field:size_t bytes_req; offset:24; size:8; signed:0;
+ field:size_t bytes_alloc; offset:32; size:8; signed:0;
+ field:gfp_t gfp_flags; offset:40; size:4; signed:0;
+
+ We'll start by creating a hist trigger that generates a simple table
+ that lists the total number of bytes requested for each function in
+ the kernel that made one or more calls to kmalloc::
+
+ # echo 'hist:key=call_site:val=bytes_req' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ This tells the tracing system to create a 'hist' trigger using the
+ call_site field of the kmalloc event as the key for the table, which
+ just means that each unique call_site address will have an entry
+ created for it in the table. The 'val=bytes_req' parameter tells
+ the hist trigger that for each unique entry (call_site) in the
+ table, it should keep a running total of the number of bytes
+ requested by that call_site.
+
+ We'll let it run for awhile and then dump the contents of the 'hist'
+ file in the kmalloc event's subdirectory (for readability, a number
+ of entries have been omitted)::
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+ { call_site: 18446744072106379007 } hitcount: 1 bytes_req: 176
+ { call_site: 18446744071579557049 } hitcount: 1 bytes_req: 1024
+ { call_site: 18446744071580608289 } hitcount: 1 bytes_req: 16384
+ { call_site: 18446744071581827654 } hitcount: 1 bytes_req: 24
+ { call_site: 18446744071580700980 } hitcount: 1 bytes_req: 8
+ { call_site: 18446744071579359876 } hitcount: 1 bytes_req: 152
+ { call_site: 18446744071580795365 } hitcount: 3 bytes_req: 144
+ { call_site: 18446744071581303129 } hitcount: 3 bytes_req: 144
+ { call_site: 18446744071580713234 } hitcount: 4 bytes_req: 2560
+ { call_site: 18446744071580933750 } hitcount: 4 bytes_req: 736
+ .
+ .
+ .
+ { call_site: 18446744072106047046 } hitcount: 69 bytes_req: 5576
+ { call_site: 18446744071582116407 } hitcount: 73 bytes_req: 2336
+ { call_site: 18446744072106054684 } hitcount: 136 bytes_req: 140504
+ { call_site: 18446744072106224230 } hitcount: 136 bytes_req: 19584
+ { call_site: 18446744072106078074 } hitcount: 153 bytes_req: 2448
+ { call_site: 18446744072106062406 } hitcount: 153 bytes_req: 36720
+ { call_site: 18446744071582507929 } hitcount: 153 bytes_req: 37088
+ { call_site: 18446744072102520590 } hitcount: 273 bytes_req: 10920
+ { call_site: 18446744071582143559 } hitcount: 358 bytes_req: 716
+ { call_site: 18446744072106465852 } hitcount: 417 bytes_req: 56712
+ { call_site: 18446744072102523378 } hitcount: 485 bytes_req: 27160
+ { call_site: 18446744072099568646 } hitcount: 1676 bytes_req: 33520
+
+ Totals:
+ Hits: 4610
+ Entries: 45
+ Dropped: 0
+
+ The output displays a line for each entry, beginning with the key
+ specified in the trigger, followed by the value(s) also specified in
+ the trigger. At the beginning of the output is a line that displays
+ the trigger info, which can also be displayed by reading the
+ 'trigger' file::
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+ hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+ At the end of the output are a few lines that display the overall
+ totals for the run. The 'Hits' field shows the total number of
+ times the event trigger was hit, the 'Entries' field shows the total
+ number of used entries in the hash table, and the 'Dropped' field
+ shows the number of hits that were dropped because the number of
+ used entries for the run exceeded the maximum number of entries
+ allowed for the table (normally 0, but if not a hint that you may
+ want to increase the size of the table using the 'size' parameter).
+
+ Notice in the above output that there's an extra field, 'hitcount',
+ which wasn't specified in the trigger. Also notice that in the
+ trigger info output, there's a parameter, 'sort=hitcount', which
+ wasn't specified in the trigger either. The reason for that is that
+ every trigger implicitly keeps a count of the total number of hits
+ attributed to a given entry, called the 'hitcount'. That hitcount
+ information is explicitly displayed in the output, and in the
+ absence of a user-specified sort parameter, is used as the default
+ sort field.
+
+ The value 'hitcount' can be used in place of an explicit value in
+ the 'values' parameter if you don't really need to have any
+ particular field summed and are mainly interested in hit
+ frequencies.
+
+ To turn the hist trigger off, simply call up the trigger in the
+ command history and re-execute it with a '!' prepended::
+
+ # echo '!hist:key=call_site:val=bytes_req' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ Finally, notice that the call_site as displayed in the output above
+ isn't really very useful. It's an address, but normally addresses
+ are displayed in hex. To have a numeric field displayed as a hex
+ value, simply append '.hex' to the field name in the trigger::
+
+ # echo 'hist:key=call_site.hex:val=bytes_req' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site.hex:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+ { call_site: ffffffffa026b291 } hitcount: 1 bytes_req: 433
+ { call_site: ffffffffa07186ff } hitcount: 1 bytes_req: 176
+ { call_site: ffffffff811ae721 } hitcount: 1 bytes_req: 16384
+ { call_site: ffffffff811c5134 } hitcount: 1 bytes_req: 8
+ { call_site: ffffffffa04a9ebb } hitcount: 1 bytes_req: 511
+ { call_site: ffffffff8122e0a6 } hitcount: 1 bytes_req: 12
+ { call_site: ffffffff8107da84 } hitcount: 1 bytes_req: 152
+ { call_site: ffffffff812d8246 } hitcount: 1 bytes_req: 24
+ { call_site: ffffffff811dc1e5 } hitcount: 3 bytes_req: 144
+ { call_site: ffffffffa02515e8 } hitcount: 3 bytes_req: 648
+ { call_site: ffffffff81258159 } hitcount: 3 bytes_req: 144
+ { call_site: ffffffff811c80f4 } hitcount: 4 bytes_req: 544
+ .
+ .
+ .
+ { call_site: ffffffffa06c7646 } hitcount: 106 bytes_req: 8024
+ { call_site: ffffffffa06cb246 } hitcount: 132 bytes_req: 31680
+ { call_site: ffffffffa06cef7a } hitcount: 132 bytes_req: 2112
+ { call_site: ffffffff8137e399 } hitcount: 132 bytes_req: 23232
+ { call_site: ffffffffa06c941c } hitcount: 185 bytes_req: 171360
+ { call_site: ffffffffa06f2a66 } hitcount: 185 bytes_req: 26640
+ { call_site: ffffffffa036a70e } hitcount: 265 bytes_req: 10600
+ { call_site: ffffffff81325447 } hitcount: 292 bytes_req: 584
+ { call_site: ffffffffa072da3c } hitcount: 446 bytes_req: 60656
+ { call_site: ffffffffa036b1f2 } hitcount: 526 bytes_req: 29456
+ { call_site: ffffffffa0099c06 } hitcount: 1780 bytes_req: 35600
+
+ Totals:
+ Hits: 4775
+ Entries: 46
+ Dropped: 0
+
+ Even that's only marginally more useful - while hex values do look
+ more like addresses, what users are typically more interested in
+ when looking at text addresses are the corresponding symbols
+ instead. To have an address displayed as symbolic value instead,
+ simply append '.sym' or '.sym-offset' to the field name in the
+ trigger::
+
+ # echo 'hist:key=call_site.sym:val=bytes_req' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=hitcount:size=2048 [active]
+
+ { call_site: [ffffffff810adcb9] syslog_print_all } hitcount: 1 bytes_req: 1024
+ { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
+ { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
+ { call_site: [ffffffff8154acbe] usb_alloc_urb } hitcount: 1 bytes_req: 192
+ { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
+ { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
+ { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
+ { call_site: [ffffffff811febd5] fsnotify_alloc_group } hitcount: 2 bytes_req: 528
+ { call_site: [ffffffff81440f58] __tty_buffer_request_room } hitcount: 2 bytes_req: 2624
+ { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 2 bytes_req: 96
+ { call_site: [ffffffffa05e19af] ieee80211_start_tx_ba_session [mac80211] } hitcount: 2 bytes_req: 464
+ { call_site: [ffffffff81672406] tcp_get_metrics } hitcount: 2 bytes_req: 304
+ { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
+ { call_site: [ffffffff81089b05] sched_create_group } hitcount: 2 bytes_req: 1424
+ .
+ .
+ .
+ { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1185 bytes_req: 123240
+ { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 1185 bytes_req: 104280
+ { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 1402 bytes_req: 190672
+ { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 1518 bytes_req: 146208
+ { call_site: [ffffffffa029070e] drm_vma_node_allow [drm] } hitcount: 1746 bytes_req: 69840
+ { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 2021 bytes_req: 792312
+ { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 2592 bytes_req: 145152
+ { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2629 bytes_req: 378576
+ { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2629 bytes_req: 3783248
+ { call_site: [ffffffff81325607] apparmor_file_alloc_security } hitcount: 5192 bytes_req: 10384
+ { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 5529 bytes_req: 110584
+ { call_site: [ffffffff8131ebf7] aa_alloc_task_context } hitcount: 21943 bytes_req: 702176
+ { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 55759 bytes_req: 5074265
+
+ Totals:
+ Hits: 109928
+ Entries: 71
+ Dropped: 0
+
+ Because the default sort key above is 'hitcount', the above shows a
+ the list of call_sites by increasing hitcount, so that at the bottom
+ we see the functions that made the most kmalloc calls during the
+ run. If instead we we wanted to see the top kmalloc callers in
+ terms of the number of bytes requested rather than the number of
+ calls, and we wanted the top caller to appear at the top, we can use
+ the 'sort' parameter, along with the 'descending' modifier::
+
+ # echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
+
+ { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2186 bytes_req: 3397464
+ { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1790 bytes_req: 712176
+ { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 8132 bytes_req: 513135
+ { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 106 bytes_req: 440128
+ { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2186 bytes_req: 314784
+ { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 2174 bytes_req: 208992
+ { call_site: [ffffffff811ae8e1] __kmalloc } hitcount: 8 bytes_req: 131072
+ { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 859 bytes_req: 116824
+ { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 1834 bytes_req: 102704
+ { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 972 bytes_req: 101088
+ { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 972 bytes_req: 85536
+ { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 3333 bytes_req: 66664
+ { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 209 bytes_req: 61632
+ .
+ .
+ .
+ { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
+ { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
+ { call_site: [ffffffff812d8406] copy_semundo } hitcount: 2 bytes_req: 48
+ { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 1 bytes_req: 48
+ { call_site: [ffffffffa027121a] drm_getmagic [drm] } hitcount: 1 bytes_req: 48
+ { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
+ { call_site: [ffffffff811c52f4] bprm_change_interp } hitcount: 2 bytes_req: 16
+ { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
+ { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
+ { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
+
+ Totals:
+ Hits: 32133
+ Entries: 81
+ Dropped: 0
+
+ To display the offset and size information in addition to the symbol
+ name, just use 'sym-offset' instead::
+
+ # echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site.sym-offset:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
+
+ { call_site: [ffffffffa046041c] i915_gem_execbuffer2+0x6c/0x2c0 [i915] } hitcount: 4569 bytes_req: 3163720
+ { call_site: [ffffffffa0489a66] intel_ring_begin+0xc6/0x1f0 [i915] } hitcount: 4569 bytes_req: 657936
+ { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23+0x694/0x1020 [i915] } hitcount: 1519 bytes_req: 472936
+ { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23+0x516/0x1020 [i915] } hitcount: 3050 bytes_req: 211832
+ { call_site: [ffffffff811e2a1b] seq_buf_alloc+0x1b/0x50 } hitcount: 34 bytes_req: 148384
+ { call_site: [ffffffffa04a580c] intel_crtc_page_flip+0xbc/0x870 [i915] } hitcount: 1385 bytes_req: 144040
+ { call_site: [ffffffff811ae8e1] __kmalloc+0x191/0x1b0 } hitcount: 8 bytes_req: 131072
+ { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl+0x282/0x360 [drm] } hitcount: 1385 bytes_req: 121880
+ { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc+0x32/0x100 [drm] } hitcount: 1848 bytes_req: 103488
+ { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state+0x2c/0xa0 [i915] } hitcount: 461 bytes_req: 62696
+ { call_site: [ffffffffa029070e] drm_vma_node_allow+0x2e/0xd0 [drm] } hitcount: 1541 bytes_req: 61640
+ { call_site: [ffffffff815f8d7b] sk_prot_alloc+0xcb/0x1b0 } hitcount: 57 bytes_req: 57456
+ .
+ .
+ .
+ { call_site: [ffffffff8109524a] alloc_fair_sched_group+0x5a/0x1a0 } hitcount: 2 bytes_req: 128
+ { call_site: [ffffffffa027b921] drm_vm_open_locked+0x31/0xa0 [drm] } hitcount: 3 bytes_req: 96
+ { call_site: [ffffffff8122e266] proc_self_follow_link+0x76/0xb0 } hitcount: 8 bytes_req: 96
+ { call_site: [ffffffff81213e80] load_elf_binary+0x240/0x1650 } hitcount: 3 bytes_req: 84
+ { call_site: [ffffffff8154bc62] usb_control_msg+0x42/0x110 } hitcount: 1 bytes_req: 8
+ { call_site: [ffffffffa00bf6fe] hidraw_send_report+0x7e/0x1a0 [hid] } hitcount: 1 bytes_req: 7
+ { call_site: [ffffffffa00bf1ca] hidraw_report_event+0x8a/0x120 [hid] } hitcount: 1 bytes_req: 7
+
+ Totals:
+ Hits: 26098
+ Entries: 64
+ Dropped: 0
+
+ We can also add multiple fields to the 'values' parameter. For
+ example, we might want to see the total number of bytes allocated
+ alongside bytes requested, and display the result sorted by bytes
+ allocated in a descending order::
+
+ # echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=call_site.sym:vals=bytes_req,bytes_alloc:sort=bytes_alloc.descending:size=2048 [active]
+
+ { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 7403 bytes_req: 4084360 bytes_alloc: 5958016
+ { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 541 bytes_req: 2213968 bytes_alloc: 2228224
+ { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 7404 bytes_req: 1066176 bytes_alloc: 1421568
+ { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1565 bytes_req: 557368 bytes_alloc: 1037760
+ { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 9557 bytes_req: 595778 bytes_alloc: 695744
+ { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 5839 bytes_req: 430680 bytes_alloc: 470400
+ { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 2388 bytes_req: 324768 bytes_alloc: 458496
+ { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 3911 bytes_req: 219016 bytes_alloc: 250304
+ { call_site: [ffffffff815f8d7b] sk_prot_alloc } hitcount: 235 bytes_req: 236880 bytes_alloc: 240640
+ { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 557 bytes_req: 169024 bytes_alloc: 221760
+ { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 9378 bytes_req: 187548 bytes_alloc: 206312
+ { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1519 bytes_req: 157976 bytes_alloc: 194432
+ .
+ .
+ .
+ { call_site: [ffffffff8109bd3b] sched_autogroup_create_attach } hitcount: 2 bytes_req: 144 bytes_alloc: 192
+ { call_site: [ffffffff81097ee8] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
+ { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
+ { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
+ { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
+ { call_site: [ffffffff81213e80] load_elf_binary } hitcount: 3 bytes_req: 84 bytes_alloc: 96
+ { call_site: [ffffffff81079a2e] kthread_create_on_node } hitcount: 1 bytes_req: 56 bytes_alloc: 64
+ { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
+ { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 bytes_alloc: 8
+ { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
+
+ Totals:
+ Hits: 66598
+ Entries: 65
+ Dropped: 0
+
+ Finally, to finish off our kmalloc example, instead of simply having
+ the hist trigger display symbolic call_sites, we can have the hist
+ trigger additionally display the complete set of kernel stack traces
+ that led to each call_site. To do that, we simply use the special
+ value 'stacktrace' for the key parameter::
+
+ # echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ The above trigger will use the kernel stack trace in effect when an
+ event is triggered as the key for the hash table. This allows the
+ enumeration of every kernel callpath that led up to a particular
+ event, along with a running total of any of the event fields for
+ that event. Here we tally bytes requested and bytes allocated for
+ every callpath in the system that led up to a kmalloc (in this case
+ every callpath to a kmalloc for a kernel compile)::
+
+ # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
+ # trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active]
+
+ { stacktrace:
+ __kmalloc_track_caller+0x10b/0x1a0
+ kmemdup+0x20/0x50
+ hidraw_report_event+0x8a/0x120 [hid]
+ hid_report_raw_event+0x3ea/0x440 [hid]
+ hid_input_report+0x112/0x190 [hid]
+ hid_irq_in+0xc2/0x260 [usbhid]
+ __usb_hcd_giveback_urb+0x72/0x120
+ usb_giveback_urb_bh+0x9e/0xe0
+ tasklet_hi_action+0xf8/0x100
+ __do_softirq+0x114/0x2c0
+ irq_exit+0xa5/0xb0
+ do_IRQ+0x5a/0xf0
+ ret_from_intr+0x0/0x30
+ cpuidle_enter+0x17/0x20
+ cpu_startup_entry+0x315/0x3e0
+ rest_init+0x7c/0x80
+ } hitcount: 3 bytes_req: 21 bytes_alloc: 24
+ { stacktrace:
+ __kmalloc_track_caller+0x10b/0x1a0
+ kmemdup+0x20/0x50
+ hidraw_report_event+0x8a/0x120 [hid]
+ hid_report_raw_event+0x3ea/0x440 [hid]
+ hid_input_report+0x112/0x190 [hid]
+ hid_irq_in+0xc2/0x260 [usbhid]
+ __usb_hcd_giveback_urb+0x72/0x120
+ usb_giveback_urb_bh+0x9e/0xe0
+ tasklet_hi_action+0xf8/0x100
+ __do_softirq+0x114/0x2c0
+ irq_exit+0xa5/0xb0
+ do_IRQ+0x5a/0xf0
+ ret_from_intr+0x0/0x30
+ } hitcount: 3 bytes_req: 21 bytes_alloc: 24
+ { stacktrace:
+ kmem_cache_alloc_trace+0xeb/0x150
+ aa_alloc_task_context+0x27/0x40
+ apparmor_cred_prepare+0x1f/0x50
+ security_prepare_creds+0x16/0x20
+ prepare_creds+0xdf/0x1a0
+ SyS_capset+0xb5/0x200
+ system_call_fastpath+0x12/0x6a
+ } hitcount: 1 bytes_req: 32 bytes_alloc: 32
+ .
+ .
+ .
+ { stacktrace:
+ __kmalloc+0x11b/0x1b0
+ i915_gem_execbuffer2+0x6c/0x2c0 [i915]
+ drm_ioctl+0x349/0x670 [drm]
+ do_vfs_ioctl+0x2f0/0x4f0
+ SyS_ioctl+0x81/0xa0
+ system_call_fastpath+0x12/0x6a
+ } hitcount: 17726 bytes_req: 13944120 bytes_alloc: 19593808
+ { stacktrace:
+ __kmalloc+0x11b/0x1b0
+ load_elf_phdrs+0x76/0xa0
+ load_elf_binary+0x102/0x1650
+ search_binary_handler+0x97/0x1d0
+ do_execveat_common.isra.34+0x551/0x6e0
+ SyS_execve+0x3a/0x50
+ return_from_execve+0x0/0x23
+ } hitcount: 33348 bytes_req: 17152128 bytes_alloc: 20226048
+ { stacktrace:
+ kmem_cache_alloc_trace+0xeb/0x150
+ apparmor_file_alloc_security+0x27/0x40
+ security_file_alloc+0x16/0x20
+ get_empty_filp+0x93/0x1c0
+ path_openat+0x31/0x5f0
+ do_filp_open+0x3a/0x90
+ do_sys_open+0x128/0x220
+ SyS_open+0x1e/0x20
+ system_call_fastpath+0x12/0x6a
+ } hitcount: 4766422 bytes_req: 9532844 bytes_alloc: 38131376
+ { stacktrace:
+ __kmalloc+0x11b/0x1b0
+ seq_buf_alloc+0x1b/0x50
+ seq_read+0x2cc/0x370
+ proc_reg_read+0x3d/0x80
+ __vfs_read+0x28/0xe0
+ vfs_read+0x86/0x140
+ SyS_read+0x46/0xb0
+ system_call_fastpath+0x12/0x6a
+ } hitcount: 19133 bytes_req: 78368768 bytes_alloc: 78368768
+
+ Totals:
+ Hits: 6085872
+ Entries: 253
+ Dropped: 0
+
+ If you key a hist trigger on common_pid, in order for example to
+ gather and display sorted totals for each process, you can use the
+ special .execname modifier to display the executable names for the
+ processes in the table rather than raw pids. The example below
+ keeps a per-process sum of total bytes read::
+
+ # echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \
+ /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
+
+ # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/hist
+ # trigger info: hist:keys=common_pid.execname:vals=count:sort=count.descending:size=2048 [active]
+
+ { common_pid: gnome-terminal [ 3196] } hitcount: 280 count: 1093512
+ { common_pid: Xorg [ 1309] } hitcount: 525 count: 256640
+ { common_pid: compiz [ 2889] } hitcount: 59 count: 254400
+ { common_pid: bash [ 8710] } hitcount: 3 count: 66369
+ { common_pid: dbus-daemon-lau [ 8703] } hitcount: 49 count: 47739
+ { common_pid: irqbalance [ 1252] } hitcount: 27 count: 27648
+ { common_pid: 01ifupdown [ 8705] } hitcount: 3 count: 17216
+ { common_pid: dbus-daemon [ 772] } hitcount: 10 count: 12396
+ { common_pid: Socket Thread [ 8342] } hitcount: 11 count: 11264
+ { common_pid: nm-dhcp-client. [ 8701] } hitcount: 6 count: 7424
+ { common_pid: gmain [ 1315] } hitcount: 18 count: 6336
+ .
+ .
+ .
+ { common_pid: postgres [ 1892] } hitcount: 2 count: 32
+ { common_pid: postgres [ 1891] } hitcount: 2 count: 32
+ { common_pid: gmain [ 8704] } hitcount: 2 count: 32
+ { common_pid: upstart-dbus-br [ 2740] } hitcount: 21 count: 21
+ { common_pid: nm-dispatcher.a [ 8696] } hitcount: 1 count: 16
+ { common_pid: indicator-datet [ 2904] } hitcount: 1 count: 16
+ { common_pid: gdbus [ 2998] } hitcount: 1 count: 16
+ { common_pid: rtkit-daemon [ 2052] } hitcount: 1 count: 8
+ { common_pid: init [ 1] } hitcount: 2 count: 2
+
+ Totals:
+ Hits: 2116
+ Entries: 51
+ Dropped: 0
+
+ Similarly, if you key a hist trigger on syscall id, for example to
+ gather and display a list of systemwide syscall hits, you can use
+ the special .syscall modifier to display the syscall names rather
+ than raw ids. The example below keeps a running total of syscall
+ counts for the system during the run::
+
+ # echo 'hist:key=id.syscall:val=hitcount' > \
+ /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
+
+ # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
+ # trigger info: hist:keys=id.syscall:vals=hitcount:sort=hitcount:size=2048 [active]
+
+ { id: sys_fsync [ 74] } hitcount: 1
+ { id: sys_newuname [ 63] } hitcount: 1
+ { id: sys_prctl [157] } hitcount: 1
+ { id: sys_statfs [137] } hitcount: 1
+ { id: sys_symlink [ 88] } hitcount: 1
+ { id: sys_sendmmsg [307] } hitcount: 1
+ { id: sys_semctl [ 66] } hitcount: 1
+ { id: sys_readlink [ 89] } hitcount: 3
+ { id: sys_bind [ 49] } hitcount: 3
+ { id: sys_getsockname [ 51] } hitcount: 3
+ { id: sys_unlink [ 87] } hitcount: 3
+ { id: sys_rename [ 82] } hitcount: 4
+ { id: unknown_syscall [ 58] } hitcount: 4
+ { id: sys_connect [ 42] } hitcount: 4
+ { id: sys_getpid [ 39] } hitcount: 4
+ .
+ .
+ .
+ { id: sys_rt_sigprocmask [ 14] } hitcount: 952
+ { id: sys_futex [202] } hitcount: 1534
+ { id: sys_write [ 1] } hitcount: 2689
+ { id: sys_setitimer [ 38] } hitcount: 2797
+ { id: sys_read [ 0] } hitcount: 3202
+ { id: sys_select [ 23] } hitcount: 3773
+ { id: sys_writev [ 20] } hitcount: 4531
+ { id: sys_poll [ 7] } hitcount: 8314
+ { id: sys_recvmsg [ 47] } hitcount: 13738
+ { id: sys_ioctl [ 16] } hitcount: 21843
+
+ Totals:
+ Hits: 67612
+ Entries: 72
+ Dropped: 0
+
+ The syscall counts above provide a rough overall picture of system
+ call activity on the system; we can see for example that the most
+ popular system call on this system was the 'sys_ioctl' system call.
+
+ We can use 'compound' keys to refine that number and provide some
+ further insight as to which processes exactly contribute to the
+ overall ioctl count.
+
+ The command below keeps a hitcount for every unique combination of
+ system call id and pid - the end result is essentially a table
+ that keeps a per-pid sum of system call hits. The results are
+ sorted using the system call id as the primary key, and the
+ hitcount sum as the secondary key::
+
+ # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \
+ /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
+
+ # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
+ # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active]
+
+ { id: sys_read [ 0], common_pid: rtkit-daemon [ 1877] } hitcount: 1
+ { id: sys_read [ 0], common_pid: gdbus [ 2976] } hitcount: 1
+ { id: sys_read [ 0], common_pid: console-kit-dae [ 3400] } hitcount: 1
+ { id: sys_read [ 0], common_pid: postgres [ 1865] } hitcount: 1
+ { id: sys_read [ 0], common_pid: deja-dup-monito [ 3543] } hitcount: 2
+ { id: sys_read [ 0], common_pid: NetworkManager [ 890] } hitcount: 2
+ { id: sys_read [ 0], common_pid: evolution-calen [ 3048] } hitcount: 2
+ { id: sys_read [ 0], common_pid: postgres [ 1864] } hitcount: 2
+ { id: sys_read [ 0], common_pid: nm-applet [ 3022] } hitcount: 2
+ { id: sys_read [ 0], common_pid: whoopsie [ 1212] } hitcount: 2
+ .
+ .
+ .
+ { id: sys_ioctl [ 16], common_pid: bash [ 8479] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: bash [ 3472] } hitcount: 12
+ { id: sys_ioctl [ 16], common_pid: gnome-terminal [ 3199] } hitcount: 16
+ { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 1808
+ { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 5580
+ .
+ .
+ .
+ { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2690] } hitcount: 3
+ { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2688] } hitcount: 16
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 975] } hitcount: 2
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 3204] } hitcount: 4
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 2888] } hitcount: 4
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 3003] } hitcount: 4
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 2873] } hitcount: 4
+ { id: sys_inotify_add_watch [254], common_pid: gmain [ 3196] } hitcount: 6
+ { id: sys_openat [257], common_pid: java [ 2623] } hitcount: 2
+ { id: sys_eventfd2 [290], common_pid: ibus-ui-gtk3 [ 2760] } hitcount: 4
+ { id: sys_eventfd2 [290], common_pid: compiz [ 2994] } hitcount: 6
+
+ Totals:
+ Hits: 31536
+ Entries: 323
+ Dropped: 0
+
+ The above list does give us a breakdown of the ioctl syscall by
+ pid, but it also gives us quite a bit more than that, which we
+ don't really care about at the moment. Since we know the syscall
+ id for sys_ioctl (16, displayed next to the sys_ioctl name), we
+ can use that to filter out all the other syscalls::
+
+ # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \
+ /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
+
+ # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
+ # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active]
+
+ { id: sys_ioctl [ 16], common_pid: gmain [ 2769] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: evolution-addre [ 8571] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: gmain [ 3003] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: gmain [ 2781] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: gmain [ 2829] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: bash [ 8726] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: bash [ 8508] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: gmain [ 2970] } hitcount: 1
+ { id: sys_ioctl [ 16], common_pid: gmain [ 2768] } hitcount: 1
+ .
+ .
+ .
+ { id: sys_ioctl [ 16], common_pid: pool [ 8559] } hitcount: 45
+ { id: sys_ioctl [ 16], common_pid: pool [ 8555] } hitcount: 48
+ { id: sys_ioctl [ 16], common_pid: pool [ 8551] } hitcount: 48
+ { id: sys_ioctl [ 16], common_pid: avahi-daemon [ 896] } hitcount: 66
+ { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 26674
+ { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 73443
+
+ Totals:
+ Hits: 101162
+ Entries: 103
+ Dropped: 0
+
+ The above output shows that 'compiz' and 'Xorg' are far and away
+ the heaviest ioctl callers (which might lead to questions about
+ whether they really need to be making all those calls and to
+ possible avenues for further investigation.)
+
+ The compound key examples used a key and a sum value (hitcount) to
+ sort the output, but we can just as easily use two keys instead.
+ Here's an example where we use a compound key composed of the the
+ common_pid and size event fields. Sorting with pid as the primary
+ key and 'size' as the secondary key allows us to display an
+ ordered summary of the recvfrom sizes, with counts, received by
+ each process::
+
+ # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \
+ /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger
+
+ # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist
+ # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active]
+
+ { common_pid: smbd [ 784], size: 4 } hitcount: 1
+ { common_pid: dnsmasq [ 1412], size: 4096 } hitcount: 672
+ { common_pid: postgres [ 1796], size: 1000 } hitcount: 6
+ { common_pid: postgres [ 1867], size: 1000 } hitcount: 10
+ { common_pid: bamfdaemon [ 2787], size: 28 } hitcount: 2
+ { common_pid: bamfdaemon [ 2787], size: 14360 } hitcount: 1
+ { common_pid: compiz [ 2994], size: 8 } hitcount: 1
+ { common_pid: compiz [ 2994], size: 20 } hitcount: 11
+ { common_pid: gnome-terminal [ 3199], size: 4 } hitcount: 2
+ { common_pid: firefox [ 8817], size: 4 } hitcount: 1
+ { common_pid: firefox [ 8817], size: 8 } hitcount: 5
+ { common_pid: firefox [ 8817], size: 588 } hitcount: 2
+ { common_pid: firefox [ 8817], size: 628 } hitcount: 1
+ { common_pid: firefox [ 8817], size: 6944 } hitcount: 1
+ { common_pid: firefox [ 8817], size: 408880 } hitcount: 2
+ { common_pid: firefox [ 8822], size: 8 } hitcount: 2
+ { common_pid: firefox [ 8822], size: 160 } hitcount: 2
+ { common_pid: firefox [ 8822], size: 320 } hitcount: 2
+ { common_pid: firefox [ 8822], size: 352 } hitcount: 1
+ .
+ .
+ .
+ { common_pid: pool [ 8923], size: 1960 } hitcount: 10
+ { common_pid: pool [ 8923], size: 2048 } hitcount: 10
+ { common_pid: pool [ 8924], size: 1960 } hitcount: 10
+ { common_pid: pool [ 8924], size: 2048 } hitcount: 10
+ { common_pid: pool [ 8928], size: 1964 } hitcount: 4
+ { common_pid: pool [ 8928], size: 1965 } hitcount: 2
+ { common_pid: pool [ 8928], size: 2048 } hitcount: 6
+ { common_pid: pool [ 8929], size: 1982 } hitcount: 1
+ { common_pid: pool [ 8929], size: 2048 } hitcount: 1
+
+ Totals:
+ Hits: 2016
+ Entries: 224
+ Dropped: 0
+
+ The above example also illustrates the fact that although a compound
+ key is treated as a single entity for hashing purposes, the sub-keys
+ it's composed of can be accessed independently.
+
+ The next example uses a string field as the hash key and
+ demonstrates how you can manually pause and continue a hist trigger.
+ In this example, we'll aggregate fork counts and don't expect a
+ large number of entries in the hash table, so we'll drop it to a
+ much smaller number, say 256::
+
+ # echo 'hist:key=child_comm:val=hitcount:size=256' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+ # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
+
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: ibus-daemon } hitcount: 1
+ { child_comm: whoopsie } hitcount: 1
+ { child_comm: smbd } hitcount: 1
+ { child_comm: gdbus } hitcount: 1
+ { child_comm: kthreadd } hitcount: 1
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: evolution-alarm } hitcount: 2
+ { child_comm: Socket Thread } hitcount: 2
+ { child_comm: postgres } hitcount: 2
+ { child_comm: bash } hitcount: 3
+ { child_comm: compiz } hitcount: 3
+ { child_comm: evolution-sourc } hitcount: 4
+ { child_comm: dhclient } hitcount: 4
+ { child_comm: pool } hitcount: 5
+ { child_comm: nm-dispatcher.a } hitcount: 8
+ { child_comm: firefox } hitcount: 8
+ { child_comm: dbus-daemon } hitcount: 8
+ { child_comm: glib-pacrunner } hitcount: 10
+ { child_comm: evolution } hitcount: 23
+
+ Totals:
+ Hits: 89
+ Entries: 20
+ Dropped: 0
+
+ If we want to pause the hist trigger, we can simply append :pause to
+ the command that started the trigger. Notice that the trigger info
+ displays as [paused]::
+
+ # echo 'hist:key=child_comm:val=hitcount:size=256:pause' >> \
+ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+ # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [paused]
+
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: kthreadd } hitcount: 1
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: gdbus } hitcount: 1
+ { child_comm: ibus-daemon } hitcount: 1
+ { child_comm: Socket Thread } hitcount: 2
+ { child_comm: evolution-alarm } hitcount: 2
+ { child_comm: smbd } hitcount: 2
+ { child_comm: bash } hitcount: 3
+ { child_comm: whoopsie } hitcount: 3
+ { child_comm: compiz } hitcount: 3
+ { child_comm: evolution-sourc } hitcount: 4
+ { child_comm: pool } hitcount: 5
+ { child_comm: postgres } hitcount: 6
+ { child_comm: firefox } hitcount: 8
+ { child_comm: dhclient } hitcount: 10
+ { child_comm: emacs } hitcount: 12
+ { child_comm: dbus-daemon } hitcount: 20
+ { child_comm: nm-dispatcher.a } hitcount: 20
+ { child_comm: evolution } hitcount: 35
+ { child_comm: glib-pacrunner } hitcount: 59
+
+ Totals:
+ Hits: 199
+ Entries: 21
+ Dropped: 0
+
+ To manually continue having the trigger aggregate events, append
+ :cont instead. Notice that the trigger info displays as [active]
+ again, and the data has changed::
+
+ # echo 'hist:key=child_comm:val=hitcount:size=256:cont' >> \
+ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+ # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
+
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: dconf worker } hitcount: 1
+ { child_comm: kthreadd } hitcount: 1
+ { child_comm: gdbus } hitcount: 1
+ { child_comm: ibus-daemon } hitcount: 1
+ { child_comm: Socket Thread } hitcount: 2
+ { child_comm: evolution-alarm } hitcount: 2
+ { child_comm: smbd } hitcount: 2
+ { child_comm: whoopsie } hitcount: 3
+ { child_comm: compiz } hitcount: 3
+ { child_comm: evolution-sourc } hitcount: 4
+ { child_comm: bash } hitcount: 5
+ { child_comm: pool } hitcount: 5
+ { child_comm: postgres } hitcount: 6
+ { child_comm: firefox } hitcount: 8
+ { child_comm: dhclient } hitcount: 11
+ { child_comm: emacs } hitcount: 12
+ { child_comm: dbus-daemon } hitcount: 22
+ { child_comm: nm-dispatcher.a } hitcount: 22
+ { child_comm: evolution } hitcount: 35
+ { child_comm: glib-pacrunner } hitcount: 59
+
+ Totals:
+ Hits: 206
+ Entries: 21
+ Dropped: 0
+
+ The previous example showed how to start and stop a hist trigger by
+ appending 'pause' and 'continue' to the hist trigger command. A
+ hist trigger can also be started in a paused state by initially
+ starting the trigger with ':pause' appended. This allows you to
+ start the trigger only when you're ready to start collecting data
+ and not before. For example, you could start the trigger in a
+ paused state, then unpause it and do something you want to measure,
+ then pause the trigger again when done.
+
+ Of course, doing this manually can be difficult and error-prone, but
+ it is possible to automatically start and stop a hist trigger based
+ on some condition, via the enable_hist and disable_hist triggers.
+
+ For example, suppose we wanted to take a look at the relative
+ weights in terms of skb length for each callpath that leads to a
+ netif_receieve_skb event when downloading a decent-sized file using
+ wget.
+
+ First we set up an initially paused stacktrace trigger on the
+ netif_receive_skb event::
+
+ # echo 'hist:key=stacktrace:vals=len:pause' > \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+ Next, we set up an 'enable_hist' trigger on the sched_process_exec
+ event, with an 'if filename==/usr/bin/wget' filter. The effect of
+ this new trigger is that it will 'unpause' the hist trigger we just
+ set up on netif_receive_skb if and only if it sees a
+ sched_process_exec event with a filename of '/usr/bin/wget'. When
+ that happens, all netif_receive_skb events are aggregated into a
+ hash table keyed on stacktrace::
+
+ # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+
+ The aggregation continues until the netif_receive_skb is paused
+ again, which is what the following disable_hist event does by
+ creating a similar setup on the sched_process_exit event, using the
+ filter 'comm==wget'::
+
+ # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+
+ Whenever a process exits and the comm field of the disable_hist
+ trigger filter matches 'comm==wget', the netif_receive_skb hist
+ trigger is disabled.
+
+ The overall effect is that netif_receive_skb events are aggregated
+ into the hash table for only the duration of the wget. Executing a
+ wget command and then listing the 'hist' file will display the
+ output generated by the wget command::
+
+ $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
+
+ # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
+ # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
+
+ { stacktrace:
+ __netif_receive_skb_core+0x46d/0x990
+ __netif_receive_skb+0x18/0x60
+ netif_receive_skb_internal+0x23/0x90
+ napi_gro_receive+0xc8/0x100
+ ieee80211_deliver_skb+0xd6/0x270 [mac80211]
+ ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
+ ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
+ ieee80211_rx+0x31d/0x900 [mac80211]
+ iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
+ iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
+ iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
+ irq_thread_fn+0x20/0x50
+ irq_thread+0x11f/0x150
+ kthread+0xd2/0xf0
+ ret_from_fork+0x42/0x70
+ } hitcount: 85 len: 28884
+ { stacktrace:
+ __netif_receive_skb_core+0x46d/0x990
+ __netif_receive_skb+0x18/0x60
+ netif_receive_skb_internal+0x23/0x90
+ napi_gro_complete+0xa4/0xe0
+ dev_gro_receive+0x23a/0x360
+ napi_gro_receive+0x30/0x100
+ ieee80211_deliver_skb+0xd6/0x270 [mac80211]
+ ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
+ ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
+ ieee80211_rx+0x31d/0x900 [mac80211]
+ iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
+ iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
+ iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
+ irq_thread_fn+0x20/0x50
+ irq_thread+0x11f/0x150
+ kthread+0xd2/0xf0
+ } hitcount: 98 len: 664329
+ { stacktrace:
+ __netif_receive_skb_core+0x46d/0x990
+ __netif_receive_skb+0x18/0x60
+ process_backlog+0xa8/0x150
+ net_rx_action+0x15d/0x340
+ __do_softirq+0x114/0x2c0
+ do_softirq_own_stack+0x1c/0x30
+ do_softirq+0x65/0x70
+ __local_bh_enable_ip+0xb5/0xc0
+ ip_finish_output+0x1f4/0x840
+ ip_output+0x6b/0xc0
+ ip_local_out_sk+0x31/0x40
+ ip_send_skb+0x1a/0x50
+ udp_send_skb+0x173/0x2a0
+ udp_sendmsg+0x2bf/0x9f0
+ inet_sendmsg+0x64/0xa0
+ sock_sendmsg+0x3d/0x50
+ } hitcount: 115 len: 13030
+ { stacktrace:
+ __netif_receive_skb_core+0x46d/0x990
+ __netif_receive_skb+0x18/0x60
+ netif_receive_skb_internal+0x23/0x90
+ napi_gro_complete+0xa4/0xe0
+ napi_gro_flush+0x6d/0x90
+ iwl_pcie_irq_handler+0x92a/0x12f0 [iwlwifi]
+ irq_thread_fn+0x20/0x50
+ irq_thread+0x11f/0x150
+ kthread+0xd2/0xf0
+ ret_from_fork+0x42/0x70
+ } hitcount: 934 len: 5512212
+
+ Totals:
+ Hits: 1232
+ Entries: 4
+ Dropped: 0
+
+ The above shows all the netif_receive_skb callpaths and their total
+ lengths for the duration of the wget command.
+
+ The 'clear' hist trigger param can be used to clear the hash table.
+ Suppose we wanted to try another run of the previous example but
+ this time also wanted to see the complete list of events that went
+ into the histogram. In order to avoid having to set everything up
+ again, we can just clear the histogram first::
+
+ # echo 'hist:key=stacktrace:vals=len:clear' >> \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+ Just to verify that it is in fact cleared, here's what we now see in
+ the hist file::
+
+ # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
+ # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
+
+ Totals:
+ Hits: 0
+ Entries: 0
+ Dropped: 0
+
+ Since we want to see the detailed list of every netif_receive_skb
+ event occurring during the new run, which are in fact the same
+ events being aggregated into the hash table, we add some additional
+ 'enable_event' events to the triggering sched_process_exec and
+ sched_process_exit events as such::
+
+ # echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+
+ # echo 'disable_event:net:netif_receive_skb if comm==wget' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+
+ If you read the trigger files for the sched_process_exec and
+ sched_process_exit triggers, you should see two triggers for each:
+ one enabling/disabling the hist aggregation and the other
+ enabling/disabling the logging of events::
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
+ enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
+ enable_hist:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
+ enable_event:net:netif_receive_skb:unlimited if comm==wget
+ disable_hist:net:netif_receive_skb:unlimited if comm==wget
+
+ In other words, whenever either of the sched_process_exec or
+ sched_process_exit events is hit and matches 'wget', it enables or
+ disables both the histogram and the event log, and what you end up
+ with is a hash table and set of events just covering the specified
+ duration. Run the wget command again::
+
+ $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
+
+ Displaying the 'hist' file should show something similar to what you
+ saw in the last run, but this time you should also see the
+ individual events in the trace file::
+
+ # cat /sys/kernel/debug/tracing/trace
+
+ # tracer: nop
+ #
+ # entries-in-buffer/entries-written: 183/1426 #P:4
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ wget-15108 [000] ..s1 31769.606929: netif_receive_skb: dev=lo skbaddr=ffff88009c353100 len=60
+ wget-15108 [000] ..s1 31769.606999: netif_receive_skb: dev=lo skbaddr=ffff88009c353200 len=60
+ dnsmasq-1382 [000] ..s1 31769.677652: netif_receive_skb: dev=lo skbaddr=ffff88009c352b00 len=130
+ dnsmasq-1382 [000] ..s1 31769.685917: netif_receive_skb: dev=lo skbaddr=ffff88009c352200 len=138
+ ##### CPU 2 buffer started ####
+ irq/29-iwlwifi-559 [002] ..s. 31772.031529: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433d00 len=2948
+ irq/29-iwlwifi-559 [002] ..s. 31772.031572: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432200 len=1500
+ irq/29-iwlwifi-559 [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948
+ irq/29-iwlwifi-559 [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948
+ irq/29-iwlwifi-559 [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500
+ .
+ .
+ .
+
+ The following example demonstrates how multiple hist triggers can be
+ attached to a given event. This capability can be useful for
+ creating a set of different summaries derived from the same set of
+ events, or for comparing the effects of different filters, among
+ other things::
+
+ # echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+ # echo 'hist:keys=skbaddr.hex:vals=len if len > 4096' >> \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+ # echo 'hist:keys=skbaddr.hex:vals=len if len == 256' >> \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+ # echo 'hist:keys=skbaddr.hex:vals=len' >> \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+ # echo 'hist:keys=len:vals=common_preempt_count' >> \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+
+ The above set of commands create four triggers differing only in
+ their filters, along with a completely different though fairly
+ nonsensical trigger. Note that in order to append multiple hist
+ triggers to the same file, you should use the '>>' operator to
+ append them ('>' will also add the new hist trigger, but will remove
+ any existing hist triggers beforehand).
+
+ Displaying the contents of the 'hist' file for the event shows the
+ contents of all five histograms::
+
+ # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
+
+ # event histogram
+ #
+ # trigger info: hist:keys=len:vals=hitcount,common_preempt_count:sort=hitcount:size=2048 [active]
+ #
+
+ { len: 176 } hitcount: 1 common_preempt_count: 0
+ { len: 223 } hitcount: 1 common_preempt_count: 0
+ { len: 4854 } hitcount: 1 common_preempt_count: 0
+ { len: 395 } hitcount: 1 common_preempt_count: 0
+ { len: 177 } hitcount: 1 common_preempt_count: 0
+ { len: 446 } hitcount: 1 common_preempt_count: 0
+ { len: 1601 } hitcount: 1 common_preempt_count: 0
+ .
+ .
+ .
+ { len: 1280 } hitcount: 66 common_preempt_count: 0
+ { len: 116 } hitcount: 81 common_preempt_count: 40
+ { len: 708 } hitcount: 112 common_preempt_count: 0
+ { len: 46 } hitcount: 221 common_preempt_count: 0
+ { len: 1264 } hitcount: 458 common_preempt_count: 0
+
+ Totals:
+ Hits: 1428
+ Entries: 147
+ Dropped: 0
+
+
+ # event histogram
+ #
+ # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
+ #
+
+ { skbaddr: ffff8800baee5e00 } hitcount: 1 len: 130
+ { skbaddr: ffff88005f3d5600 } hitcount: 1 len: 1280
+ { skbaddr: ffff88005f3d4900 } hitcount: 1 len: 1280
+ { skbaddr: ffff88009fed6300 } hitcount: 1 len: 115
+ { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 115
+ { skbaddr: ffff88008cdb1900 } hitcount: 1 len: 46
+ { skbaddr: ffff880064b5ef00 } hitcount: 1 len: 118
+ { skbaddr: ffff880044e3c700 } hitcount: 1 len: 60
+ { skbaddr: ffff880100065900 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d46bd500 } hitcount: 1 len: 116
+ { skbaddr: ffff88005f3d5f00 } hitcount: 1 len: 1280
+ { skbaddr: ffff880100064700 } hitcount: 1 len: 365
+ { skbaddr: ffff8800badb6f00 } hitcount: 1 len: 60
+ .
+ .
+ .
+ { skbaddr: ffff88009fe0be00 } hitcount: 27 len: 24677
+ { skbaddr: ffff88009fe0a400 } hitcount: 27 len: 23052
+ { skbaddr: ffff88009fe0b700 } hitcount: 31 len: 25589
+ { skbaddr: ffff88009fe0b600 } hitcount: 32 len: 27326
+ { skbaddr: ffff88006a462800 } hitcount: 68 len: 71678
+ { skbaddr: ffff88006a463700 } hitcount: 70 len: 72678
+ { skbaddr: ffff88006a462b00 } hitcount: 71 len: 77589
+ { skbaddr: ffff88006a463600 } hitcount: 73 len: 71307
+ { skbaddr: ffff88006a462200 } hitcount: 81 len: 81032
+
+ Totals:
+ Hits: 1451
+ Entries: 318
+ Dropped: 0
+
+
+ # event histogram
+ #
+ # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len == 256 [active]
+ #
+
+
+ Totals:
+ Hits: 0
+ Entries: 0
+ Dropped: 0
+
+
+ # event histogram
+ #
+ # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len > 4096 [active]
+ #
+
+ { skbaddr: ffff88009fd2c300 } hitcount: 1 len: 7212
+ { skbaddr: ffff8800d2bcce00 } hitcount: 1 len: 7212
+ { skbaddr: ffff8800d2bcd700 } hitcount: 1 len: 7212
+ { skbaddr: ffff8800d2bcda00 } hitcount: 1 len: 21492
+ { skbaddr: ffff8800ae2e2d00 } hitcount: 1 len: 7212
+ { skbaddr: ffff8800d2bcdb00 } hitcount: 1 len: 7212
+ { skbaddr: ffff88006a4df500 } hitcount: 1 len: 4854
+ { skbaddr: ffff88008ce47b00 } hitcount: 1 len: 18636
+ { skbaddr: ffff8800ae2e2200 } hitcount: 1 len: 12924
+ { skbaddr: ffff88005f3e1000 } hitcount: 1 len: 4356
+ { skbaddr: ffff8800d2bcdc00 } hitcount: 2 len: 24420
+ { skbaddr: ffff8800d2bcc200 } hitcount: 2 len: 12996
+
+ Totals:
+ Hits: 14
+ Entries: 12
+ Dropped: 0
+
+
+ # event histogram
+ #
+ # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len < 0 [active]
+ #
+
+
+ Totals:
+ Hits: 0
+ Entries: 0
+ Dropped: 0
+
+ Named triggers can be used to have triggers share a common set of
+ histogram data. This capability is mostly useful for combining the
+ output of events generated by tracepoints contained inside inline
+ functions, but names can be used in a hist trigger on any event.
+ For example, these two triggers when hit will update the same 'len'
+ field in the shared 'foo' histogram data::
+
+ # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
+ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
+ # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
+ /sys/kernel/debug/tracing/events/net/netif_rx/trigger
+
+ You can see that they're updating common histogram data by reading
+ each event's hist files at the same time::
+
+ # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist;
+ cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
+
+ # event histogram
+ #
+ # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
+ #
+
+ { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46
+ { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76
+ { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468
+ { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46
+ { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52
+ { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168
+ { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260
+ { skbaddr: ffff880064505000 } hitcount: 1 len: 46
+ { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32
+ { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44
+ { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168
+ { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40
+ { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40
+ { skbaddr: ffff880064505f00 } hitcount: 1 len: 174
+ { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160
+ { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76
+ { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32
+ { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988
+ { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46
+ { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44
+ { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676
+ { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107
+ { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92
+ { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142
+ { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220
+ { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92
+ { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92
+ { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675
+ { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138
+ { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138
+ { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184
+ { skbaddr: ffff880064504400 } hitcount: 4 len: 184
+ { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184
+ { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230
+ { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196
+ { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276
+ { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276
+
+ Totals:
+ Hits: 81
+ Entries: 42
+ Dropped: 0
+ # event histogram
+ #
+ # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
+ #
+
+ { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46
+ { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76
+ { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468
+ { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46
+ { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52
+ { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168
+ { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260
+ { skbaddr: ffff880064505000 } hitcount: 1 len: 46
+ { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32
+ { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44
+ { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168
+ { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40
+ { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40
+ { skbaddr: ffff880064505f00 } hitcount: 1 len: 174
+ { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160
+ { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76
+ { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32
+ { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46
+ { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988
+ { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46
+ { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44
+ { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676
+ { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107
+ { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92
+ { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142
+ { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220
+ { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92
+ { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92
+ { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675
+ { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138
+ { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138
+ { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184
+ { skbaddr: ffff880064504400 } hitcount: 4 len: 184
+ { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184
+ { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230
+ { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196
+ { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276
+ { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276
+
+ Totals:
+ Hits: 81
+ Entries: 42
+ Dropped: 0
+
+ And here's an example that shows how to combine histogram data from
+ any two events even if they don't share any 'compatible' fields
+ other than 'hitcount' and 'stacktrace'. These commands create a
+ couple of triggers named 'bar' using those fields::
+
+ # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
+ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
+ # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
+ /sys/kernel/debug/tracing/events/net/netif_rx/trigger
+
+ And displaying the output of either shows some interesting if
+ somewhat confusing output::
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
+ # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
+
+ # event histogram
+ #
+ # trigger info: hist:name=bar:keys=stacktrace:vals=hitcount:sort=hitcount:size=2048 [active]
+ #
+
+ { stacktrace:
+ _do_fork+0x18e/0x330
+ kernel_thread+0x29/0x30
+ kthreadd+0x154/0x1b0
+ ret_from_fork+0x3f/0x70
+ } hitcount: 1
+ { stacktrace:
+ netif_rx_internal+0xb2/0xd0
+ netif_rx_ni+0x20/0x70
+ dev_loopback_xmit+0xaa/0xd0
+ ip_mc_output+0x126/0x240
+ ip_local_out_sk+0x31/0x40
+ igmp_send_report+0x1e9/0x230
+ igmp_timer_expire+0xe9/0x120
+ call_timer_fn+0x39/0xf0
+ run_timer_softirq+0x1e1/0x290
+ __do_softirq+0xfd/0x290
+ irq_exit+0x98/0xb0
+ smp_apic_timer_interrupt+0x4a/0x60
+ apic_timer_interrupt+0x6d/0x80
+ cpuidle_enter+0x17/0x20
+ call_cpuidle+0x3b/0x60
+ cpu_startup_entry+0x22d/0x310
+ } hitcount: 1
+ { stacktrace:
+ netif_rx_internal+0xb2/0xd0
+ netif_rx_ni+0x20/0x70
+ dev_loopback_xmit+0xaa/0xd0
+ ip_mc_output+0x17f/0x240
+ ip_local_out_sk+0x31/0x40
+ ip_send_skb+0x1a/0x50
+ udp_send_skb+0x13e/0x270
+ udp_sendmsg+0x2bf/0x980
+ inet_sendmsg+0x67/0xa0
+ sock_sendmsg+0x38/0x50
+ SYSC_sendto+0xef/0x170
+ SyS_sendto+0xe/0x10
+ entry_SYSCALL_64_fastpath+0x12/0x6a
+ } hitcount: 2
+ { stacktrace:
+ netif_rx_internal+0xb2/0xd0
+ netif_rx+0x1c/0x60
+ loopback_xmit+0x6c/0xb0
+ dev_hard_start_xmit+0x219/0x3a0
+ __dev_queue_xmit+0x415/0x4f0
+ dev_queue_xmit_sk+0x13/0x20
+ ip_finish_output2+0x237/0x340
+ ip_finish_output+0x113/0x1d0
+ ip_output+0x66/0xc0
+ ip_local_out_sk+0x31/0x40
+ ip_send_skb+0x1a/0x50
+ udp_send_skb+0x16d/0x270
+ udp_sendmsg+0x2bf/0x980
+ inet_sendmsg+0x67/0xa0
+ sock_sendmsg+0x38/0x50
+ ___sys_sendmsg+0x14e/0x270
+ } hitcount: 76
+ { stacktrace:
+ netif_rx_internal+0xb2/0xd0
+ netif_rx+0x1c/0x60
+ loopback_xmit+0x6c/0xb0
+ dev_hard_start_xmit+0x219/0x3a0
+ __dev_queue_xmit+0x415/0x4f0
+ dev_queue_xmit_sk+0x13/0x20
+ ip_finish_output2+0x237/0x340
+ ip_finish_output+0x113/0x1d0
+ ip_output+0x66/0xc0
+ ip_local_out_sk+0x31/0x40
+ ip_send_skb+0x1a/0x50
+ udp_send_skb+0x16d/0x270
+ udp_sendmsg+0x2bf/0x980
+ inet_sendmsg+0x67/0xa0
+ sock_sendmsg+0x38/0x50
+ ___sys_sendmsg+0x269/0x270
+ } hitcount: 77
+ { stacktrace:
+ netif_rx_internal+0xb2/0xd0
+ netif_rx+0x1c/0x60
+ loopback_xmit+0x6c/0xb0
+ dev_hard_start_xmit+0x219/0x3a0
+ __dev_queue_xmit+0x415/0x4f0
+ dev_queue_xmit_sk+0x13/0x20
+ ip_finish_output2+0x237/0x340
+ ip_finish_output+0x113/0x1d0
+ ip_output+0x66/0xc0
+ ip_local_out_sk+0x31/0x40
+ ip_send_skb+0x1a/0x50
+ udp_send_skb+0x16d/0x270
+ udp_sendmsg+0x2bf/0x980
+ inet_sendmsg+0x67/0xa0
+ sock_sendmsg+0x38/0x50
+ SYSC_sendto+0xef/0x170
+ } hitcount: 88
+ { stacktrace:
+ _do_fork+0x18e/0x330
+ SyS_clone+0x19/0x20
+ entry_SYSCALL_64_fastpath+0x12/0x6a
+ } hitcount: 244
+
+ Totals:
+ Hits: 489
+ Entries: 7
+ Dropped: 0
+
+2.2 Inter-event hist triggers
+-----------------------------
+
+Inter-event hist triggers are hist triggers that combine values from
+one or more other events and create a histogram using that data. Data
+from an inter-event histogram can in turn become the source for
+further combined histograms, thus providing a chain of related
+histograms, which is important for some applications.
+
+The most important example of an inter-event quantity that can be used
+in this manner is latency, which is simply a difference in timestamps
+between two events. Although latency is the most important
+inter-event quantity, note that because the support is completely
+general across the trace event subsystem, any event field can be used
+in an inter-event quantity.
+
+An example of a histogram that combines data from other histograms
+into a useful chain would be a 'wakeupswitch latency' histogram that
+combines a 'wakeup latency' histogram and a 'switch latency'
+histogram.
+
+Normally, a hist trigger specification consists of a (possibly
+compound) key along with one or more numeric values, which are
+continually updated sums associated with that key. A histogram
+specification in this case consists of individual key and value
+specifications that refer to trace event fields associated with a
+single event type.
+
+The inter-event hist trigger extension allows fields from multiple
+events to be referenced and combined into a multi-event histogram
+specification. In support of this overall goal, a few enabling
+features have been added to the hist trigger support:
+
+ - In order to compute an inter-event quantity, a value from one
+ event needs to saved and then referenced from another event. This
+ requires the introduction of support for histogram 'variables'.
+
+ - The computation of inter-event quantities and their combination
+ require some minimal amount of support for applying simple
+ expressions to variables (+ and -).
+
+ - A histogram consisting of inter-event quantities isn't logically a
+ histogram on either event (so having the 'hist' file for either
+ event host the histogram output doesn't really make sense). To
+ address the idea that the histogram is associated with a
+ combination of events, support is added allowing the creation of
+ 'synthetic' events that are events derived from other events.
+ These synthetic events are full-fledged events just like any other
+ and can be used as such, as for instance to create the
+ 'combination' histograms mentioned previously.
+
+ - A set of 'actions' can be associated with histogram entries -
+ these can be used to generate the previously mentioned synthetic
+ events, but can also be used for other purposes, such as for
+ example saving context when a 'max' latency has been hit.
+
+ - Trace events don't have a 'timestamp' associated with them, but
+ there is an implicit timestamp saved along with an event in the
+ underlying ftrace ring buffer. This timestamp is now exposed as a
+ a synthetic field named 'common_timestamp' which can be used in
+ histograms as if it were any other event field; it isn't an actual
+ field in the trace format but rather is a synthesized value that
+ nonetheless can be used as if it were an actual field. By default
+ it is in units of nanoseconds; appending '.usecs' to a
+ common_timestamp field changes the units to microseconds.
+
+A note on inter-event timestamps: If common_timestamp is used in a
+histogram, the trace buffer is automatically switched over to using
+absolute timestamps and the "global" trace clock, in order to avoid
+bogus timestamp differences with other clocks that aren't coherent
+across CPUs. This can be overridden by specifying one of the other
+trace clocks instead, using the "clock=XXX" hist trigger attribute,
+where XXX is any of the clocks listed in the tracing/trace_clock
+pseudo-file.
+
+These features are described in more detail in the following sections.
+
+2.2.1 Histogram Variables
+-------------------------
+
+Variables are simply named locations used for saving and retrieving
+values between matching events. A 'matching' event is defined as an
+event that has a matching key - if a variable is saved for a histogram
+entry corresponding to that key, any subsequent event with a matching
+key can access that variable.
+
+A variable's value is normally available to any subsequent event until
+it is set to something else by a subsequent event. The one exception
+to that rule is that any variable used in an expression is essentially
+'read-once' - once it's used by an expression in a subsequent event,
+it's reset to its 'unset' state, which means it can't be used again
+unless it's set again. This ensures not only that an event doesn't
+use an uninitialized variable in a calculation, but that that variable
+is used only once and not for any unrelated subsequent match.
+
+The basic syntax for saving a variable is to simply prefix a unique
+variable name not corresponding to any keyword along with an '=' sign
+to any event field.
+
+Either keys or values can be saved and retrieved in this way. This
+creates a variable named 'ts0' for a histogram entry with the key
+'next_pid'::
+
+ # echo 'hist:keys=next_pid:vals=$ts0:ts0=common_timestamp ... >> \
+ event/trigger
+
+The ts0 variable can be accessed by any subsequent event having the
+same pid as 'next_pid'.
+
+Variable references are formed by prepending the variable name with
+the '$' sign. Thus for example, the ts0 variable above would be
+referenced as '$ts0' in expressions.
+
+Because 'vals=' is used, the common_timestamp variable value above
+will also be summed as a normal histogram value would (though for a
+timestamp it makes little sense).
+
+The below shows that a key value can also be saved in the same way::
+
+ # echo 'hist:timer_pid=common_pid:key=timer_pid ...' >> event/trigger
+
+If a variable isn't a key variable or prefixed with 'vals=', the
+associated event field will be saved in a variable but won't be summed
+as a value::
+
+ # echo 'hist:keys=next_pid:ts1=common_timestamp ...' >> event/trigger
+
+Multiple variables can be assigned at the same time. The below would
+result in both ts0 and b being created as variables, with both
+common_timestamp and field1 additionally being summed as values::
+
+ # echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ...' >> \
+ event/trigger
+
+Note that variable assignments can appear either preceding or
+following their use. The command below behaves identically to the
+command above::
+
+ # echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ...' >> \
+ event/trigger
+
+Any number of variables not bound to a 'vals=' prefix can also be
+assigned by simply separating them with colons. Below is the same
+thing but without the values being summed in the histogram::
+
+ # echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ...' >> event/trigger
+
+Variables set as above can be referenced and used in expressions on
+another event.
+
+For example, here's how a latency can be calculated::
+
+ # echo 'hist:keys=pid,prio:ts0=common_timestamp ...' >> event1/trigger
+ # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ...' >> event2/trigger
+
+In the first line above, the event's timetamp is saved into the
+variable ts0. In the next line, ts0 is subtracted from the second
+event's timestamp to produce the latency, which is then assigned into
+yet another variable, 'wakeup_lat'. The hist trigger below in turn
+makes use of the wakeup_lat variable to compute a combined latency
+using the same key and variable from yet another event::
+
+ # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ...' >> event3/trigger
+
+2.2.2 Synthetic Events
+----------------------
+
+Synthetic events are user-defined events generated from hist trigger
+variables or fields associated with one or more other events. Their
+purpose is to provide a mechanism for displaying data spanning
+multiple events consistent with the existing and already familiar
+usage for normal events.
+
+To define a synthetic event, the user writes a simple specification
+consisting of the name of the new event along with one or more
+variables and their types, which can be any valid field type,
+separated by semicolons, to the tracing/synthetic_events file.
+
+For instance, the following creates a new event named 'wakeup_latency'
+with 3 fields: lat, pid, and prio. Each of those fields is simply a
+variable reference to a variable on another event::
+
+ # echo 'wakeup_latency \
+ u64 lat; \
+ pid_t pid; \
+ int prio' >> \
+ /sys/kernel/debug/tracing/synthetic_events
+
+Reading the tracing/synthetic_events file lists all the currently
+defined synthetic events, in this case the event defined above::
+
+ # cat /sys/kernel/debug/tracing/synthetic_events
+ wakeup_latency u64 lat; pid_t pid; int prio
+
+An existing synthetic event definition can be removed by prepending
+the command that defined it with a '!'::
+
+ # echo '!wakeup_latency u64 lat pid_t pid int prio' >> \
+ /sys/kernel/debug/tracing/synthetic_events
+
+At this point, there isn't yet an actual 'wakeup_latency' event
+instantiated in the event subsytem - for this to happen, a 'hist
+trigger action' needs to be instantiated and bound to actual fields
+and variables defined on other events (see Section 2.2.3 below on
+how that is done using hist trigger 'onmatch' action). Once that is
+done, the 'wakeup_latency' synthetic event instance is created.
+
+A histogram can now be defined for the new synthetic event::
+
+ # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \
+ /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
+
+The new event is created under the tracing/events/synthetic/ directory
+and looks and behaves just like any other event::
+
+ # ls /sys/kernel/debug/tracing/events/synthetic/wakeup_latency
+ enable filter format hist id trigger
+
+Like any other event, once a histogram is enabled for the event, the
+output can be displayed by reading the event's 'hist' file.
+
+2.2.3 Hist trigger 'actions'
+----------------------------
+
+A hist trigger 'action' is a function that's executed whenever a
+histogram entry is added or updated.
+
+The default 'action' if no special function is explicity specified is
+as it always has been, to simply update the set of values associated
+with an entry. Some applications, however, may want to perform
+additional actions at that point, such as generate another event, or
+compare and save a maximum.
+
+The following additional actions are available. To specify an action
+for a given event, simply specify the action between colons in the
+hist trigger specification.
+
+ - onmatch(matching.event).<synthetic_event_name>(param list)
+
+ The 'onmatch(matching.event).<synthetic_event_name>(params)' hist
+ trigger action is invoked whenever an event matches and the
+ histogram entry would be added or updated. It causes the named
+ synthetic event to be generated with the values given in the
+ 'param list'. The result is the generation of a synthetic event
+ that consists of the values contained in those variables at the
+ time the invoking event was hit.
+
+ The 'param list' consists of one or more parameters which may be
+ either variables or fields defined on either the 'matching.event'
+ or the target event. The variables or fields specified in the
+ param list may be either fully-qualified or unqualified. If a
+ variable is specified as unqualified, it must be unique between
+ the two events. A field name used as a param can be unqualified
+ if it refers to the target event, but must be fully qualified if
+ it refers to the matching event. A fully-qualified name is of the
+ form 'system.event_name.$var_name' or 'system.event_name.field'.
+
+ The 'matching.event' specification is simply the fully qualified
+ event name of the event that matches the target event for the
+ onmatch() functionality, in the form 'system.event_name'.
+
+ Finally, the number and type of variables/fields in the 'param
+ list' must match the number and types of the fields in the
+ synthetic event being generated.
+
+ As an example the below defines a simple synthetic event and uses
+ a variable defined on the sched_wakeup_new event as a parameter
+ when invoking the synthetic event. Here we define the synthetic
+ event::
+
+ # echo 'wakeup_new_test pid_t pid' >> \
+ /sys/kernel/debug/tracing/synthetic_events
+
+ # cat /sys/kernel/debug/tracing/synthetic_events
+ wakeup_new_test pid_t pid
+
+ The following hist trigger both defines the missing testpid
+ variable and specifies an onmatch() action that generates a
+ wakeup_new_test synthetic event whenever a sched_wakeup_new event
+ occurs, which because of the 'if comm == "cyclictest"' filter only
+ happens when the executable is cyclictest::
+
+ # echo 'hist:keys=$testpid:testpid=pid:onmatch(sched.sched_wakeup_new).\
+ wakeup_new_test($testpid) if comm=="cyclictest"' >> \
+ /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger
+
+ Creating and displaying a histogram based on those events is now
+ just a matter of using the fields and new synthetic event in the
+ tracing/events/synthetic directory, as usual::
+
+ # echo 'hist:keys=pid:sort=pid' >> \
+ /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/trigger
+
+ Running 'cyclictest' should cause wakeup_new events to generate
+ wakeup_new_test synthetic events which should result in histogram
+ output in the wakeup_new_test event's hist file::
+
+ # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/hist
+
+ A more typical usage would be to use two events to calculate a
+ latency. The following example uses a set of hist triggers to
+ produce a 'wakeup_latency' histogram.
+
+ First, we define a 'wakeup_latency' synthetic event::
+
+ # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \
+ /sys/kernel/debug/tracing/synthetic_events
+
+ Next, we specify that whenever we see a sched_waking event for a
+ cyclictest thread, save the timestamp in a 'ts0' variable::
+
+ # echo 'hist:keys=$saved_pid:saved_pid=pid:ts0=common_timestamp.usecs \
+ if comm=="cyclictest"' >> \
+ /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
+
+ Then, when the corresponding thread is actually scheduled onto the
+ CPU by a sched_switch event, calculate the latency and use that
+ along with another variable and an event field to generate a
+ wakeup_latency synthetic event::
+
+ # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0:\
+ onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,\
+ $saved_pid,next_prio) if next_comm=="cyclictest"' >> \
+ /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
+
+ We also need to create a histogram on the wakeup_latency synthetic
+ event in order to aggregate the generated synthetic event data::
+
+ # echo 'hist:keys=pid,prio,lat:sort=pid,lat' >> \
+ /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
+
+ Finally, once we've run cyclictest to actually generate some
+ events, we can see the output by looking at the wakeup_latency
+ synthetic event's hist file::
+
+ # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist
+
+ - onmax(var).save(field,.. .)
+
+ The 'onmax(var).save(field,...)' hist trigger action is invoked
+ whenever the value of 'var' associated with a histogram entry
+ exceeds the current maximum contained in that variable.
+
+ The end result is that the trace event fields specified as the
+ onmax.save() params will be saved if 'var' exceeds the current
+ maximum for that hist trigger entry. This allows context from the
+ event that exhibited the new maximum to be saved for later
+ reference. When the histogram is displayed, additional fields
+ displaying the saved values will be printed.
+
+ As an example the below defines a couple of hist triggers, one for
+ sched_waking and another for sched_switch, keyed on pid. Whenever
+ a sched_waking occurs, the timestamp is saved in the entry
+ corresponding to the current pid, and when the scheduler switches
+ back to that pid, the timestamp difference is calculated. If the
+ resulting latency, stored in wakeup_lat, exceeds the current
+ maximum latency, the values specified in the save() fields are
+ recorded::
+
+ # echo 'hist:keys=pid:ts0=common_timestamp.usecs \
+ if comm=="cyclictest"' >> \
+ /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
+
+ # echo 'hist:keys=next_pid:\
+ wakeup_lat=common_timestamp.usecs-$ts0:\
+ onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) \
+ if next_comm=="cyclictest"' >> \
+ /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
+
+ When the histogram is displayed, the max value and the saved
+ values corresponding to the max are displayed following the rest
+ of the fields::
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist
+ { next_pid: 2255 } hitcount: 239
+ common_timestamp-ts0: 0
+ max: 27
+ next_comm: cyclictest
+ prev_pid: 0 prev_prio: 120 prev_comm: swapper/1
+
+ { next_pid: 2256 } hitcount: 2355
+ common_timestamp-ts0: 0
+ max: 49 next_comm: cyclictest
+ prev_pid: 0 prev_prio: 120 prev_comm: swapper/0
+
+ Totals:
+ Hits: 12970
+ Entries: 2
+ Dropped: 0
+
+3. User space creating a trigger
+--------------------------------
+
+Writing into /sys/kernel/tracing/trace_marker writes into the ftrace
+ring buffer. This can also act like an event, by writing into the trigger
+file located in /sys/kernel/tracing/events/ftrace/print/
+
+Modifying cyclictest to write into the trace_marker file before it sleeps
+and after it wakes up, something like this::
+
+ static void traceputs(char *str)
+ {
+ /* tracemark_fd is the trace_marker file descriptor */
+ if (tracemark_fd < 0)
+ return;
+ /* write the tracemark message */
+ write(tracemark_fd, str, strlen(str));
+ }
+
+And later add something like::
+
+ traceputs("start");
+ clock_nanosleep(...);
+ traceputs("end");
+
+We can make a histogram from this::
+
+ # cd /sys/kernel/tracing
+ # echo 'latency u64 lat' > synthetic_events
+ # echo 'hist:keys=common_pid:ts0=common_timestamp.usecs if buf == "start"' > events/ftrace/print/trigger
+ # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(ftrace.print).latency($lat) if buf == "end"' >> events/ftrace/print/trigger
+ # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger
+
+The above created a synthetic event called "latency" and two histograms
+against the trace_marker, one gets triggered when "start" is written into the
+trace_marker file and the other when "end" is written. If the pids match, then
+it will call the "latency" synthetic event with the calculated latency as its
+parameter. Finally, a histogram is added to the latency synthetic event to
+record the calculated latency along with the pid.
+
+Now running cyclictest with::
+
+ # ./cyclictest -p80 -d0 -i250 -n -a -t --tracemark -b 1000
+
+ -p80 : run threads at priority 80
+ -d0 : have all threads run at the same interval
+ -i250 : start the interval at 250 microseconds (all threads will do this)
+ -n : sleep with nanosleep
+ -a : affine all threads to a separate CPU
+ -t : one thread per available CPU
+ --tracemark : enable trace mark writing
+ -b 1000 : stop if any latency is greater than 1000 microseconds
+
+Note, the -b 1000 is used just to make --tracemark available.
+
+Then we can see the histogram created by this with::
+
+ # cat events/synthetic/latency/hist
+ # event histogram
+ #
+ # trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active]
+ #
+
+ { lat: 107, common_pid: 2039 } hitcount: 1
+ { lat: 122, common_pid: 2041 } hitcount: 1
+ { lat: 166, common_pid: 2039 } hitcount: 1
+ { lat: 174, common_pid: 2039 } hitcount: 1
+ { lat: 194, common_pid: 2041 } hitcount: 1
+ { lat: 196, common_pid: 2036 } hitcount: 1
+ { lat: 197, common_pid: 2038 } hitcount: 1
+ { lat: 198, common_pid: 2039 } hitcount: 1
+ { lat: 199, common_pid: 2039 } hitcount: 1
+ { lat: 200, common_pid: 2041 } hitcount: 1
+ { lat: 201, common_pid: 2039 } hitcount: 2
+ { lat: 202, common_pid: 2038 } hitcount: 1
+ { lat: 202, common_pid: 2043 } hitcount: 1
+ { lat: 203, common_pid: 2039 } hitcount: 1
+ { lat: 203, common_pid: 2036 } hitcount: 1
+ { lat: 203, common_pid: 2041 } hitcount: 1
+ { lat: 206, common_pid: 2038 } hitcount: 2
+ { lat: 207, common_pid: 2039 } hitcount: 1
+ { lat: 207, common_pid: 2036 } hitcount: 1
+ { lat: 208, common_pid: 2040 } hitcount: 1
+ { lat: 209, common_pid: 2043 } hitcount: 1
+ { lat: 210, common_pid: 2039 } hitcount: 1
+ { lat: 211, common_pid: 2039 } hitcount: 4
+ { lat: 212, common_pid: 2043 } hitcount: 1
+ { lat: 212, common_pid: 2039 } hitcount: 2
+ { lat: 213, common_pid: 2039 } hitcount: 1
+ { lat: 214, common_pid: 2038 } hitcount: 1
+ { lat: 214, common_pid: 2039 } hitcount: 2
+ { lat: 214, common_pid: 2042 } hitcount: 1
+ { lat: 215, common_pid: 2039 } hitcount: 1
+ { lat: 217, common_pid: 2036 } hitcount: 1
+ { lat: 217, common_pid: 2040 } hitcount: 1
+ { lat: 217, common_pid: 2039 } hitcount: 1
+ { lat: 218, common_pid: 2039 } hitcount: 6
+ { lat: 219, common_pid: 2039 } hitcount: 9
+ { lat: 220, common_pid: 2039 } hitcount: 11
+ { lat: 221, common_pid: 2039 } hitcount: 5
+ { lat: 221, common_pid: 2042 } hitcount: 1
+ { lat: 222, common_pid: 2039 } hitcount: 7
+ { lat: 223, common_pid: 2036 } hitcount: 1
+ { lat: 223, common_pid: 2039 } hitcount: 3
+ { lat: 224, common_pid: 2039 } hitcount: 4
+ { lat: 224, common_pid: 2037 } hitcount: 1
+ { lat: 224, common_pid: 2036 } hitcount: 2
+ { lat: 225, common_pid: 2039 } hitcount: 5
+ { lat: 225, common_pid: 2042 } hitcount: 1
+ { lat: 226, common_pid: 2039 } hitcount: 7
+ { lat: 226, common_pid: 2036 } hitcount: 4
+ { lat: 227, common_pid: 2039 } hitcount: 6
+ { lat: 227, common_pid: 2036 } hitcount: 12
+ { lat: 227, common_pid: 2043 } hitcount: 1
+ { lat: 228, common_pid: 2039 } hitcount: 7
+ { lat: 228, common_pid: 2036 } hitcount: 14
+ { lat: 229, common_pid: 2039 } hitcount: 9
+ { lat: 229, common_pid: 2036 } hitcount: 8
+ { lat: 229, common_pid: 2038 } hitcount: 1
+ { lat: 230, common_pid: 2039 } hitcount: 11
+ { lat: 230, common_pid: 2036 } hitcount: 6
+ { lat: 230, common_pid: 2043 } hitcount: 1
+ { lat: 230, common_pid: 2042 } hitcount: 2
+ { lat: 231, common_pid: 2041 } hitcount: 1
+ { lat: 231, common_pid: 2036 } hitcount: 6
+ { lat: 231, common_pid: 2043 } hitcount: 1
+ { lat: 231, common_pid: 2039 } hitcount: 8
+ { lat: 232, common_pid: 2037 } hitcount: 1
+ { lat: 232, common_pid: 2039 } hitcount: 6
+ { lat: 232, common_pid: 2040 } hitcount: 2
+ { lat: 232, common_pid: 2036 } hitcount: 5
+ { lat: 232, common_pid: 2043 } hitcount: 1
+ { lat: 233, common_pid: 2036 } hitcount: 5
+ { lat: 233, common_pid: 2039 } hitcount: 11
+ { lat: 234, common_pid: 2039 } hitcount: 4
+ { lat: 234, common_pid: 2038 } hitcount: 2
+ { lat: 234, common_pid: 2043 } hitcount: 2
+ { lat: 234, common_pid: 2036 } hitcount: 11
+ { lat: 234, common_pid: 2040 } hitcount: 1
+ { lat: 235, common_pid: 2037 } hitcount: 2
+ { lat: 235, common_pid: 2036 } hitcount: 8
+ { lat: 235, common_pid: 2043 } hitcount: 2
+ { lat: 235, common_pid: 2039 } hitcount: 5
+ { lat: 235, common_pid: 2042 } hitcount: 2
+ { lat: 235, common_pid: 2040 } hitcount: 4
+ { lat: 235, common_pid: 2041 } hitcount: 1
+ { lat: 236, common_pid: 2036 } hitcount: 7
+ { lat: 236, common_pid: 2037 } hitcount: 1
+ { lat: 236, common_pid: 2041 } hitcount: 5
+ { lat: 236, common_pid: 2039 } hitcount: 3
+ { lat: 236, common_pid: 2043 } hitcount: 9
+ { lat: 236, common_pid: 2040 } hitcount: 7
+ { lat: 237, common_pid: 2037 } hitcount: 1
+ { lat: 237, common_pid: 2040 } hitcount: 1
+ { lat: 237, common_pid: 2036 } hitcount: 9
+ { lat: 237, common_pid: 2039 } hitcount: 3
+ { lat: 237, common_pid: 2043 } hitcount: 8
+ { lat: 237, common_pid: 2042 } hitcount: 2
+ { lat: 237, common_pid: 2041 } hitcount: 2
+ { lat: 238, common_pid: 2043 } hitcount: 10
+ { lat: 238, common_pid: 2040 } hitcount: 1
+ { lat: 238, common_pid: 2037 } hitcount: 9
+ { lat: 238, common_pid: 2038 } hitcount: 1
+ { lat: 238, common_pid: 2039 } hitcount: 1
+ { lat: 238, common_pid: 2042 } hitcount: 3
+ { lat: 238, common_pid: 2036 } hitcount: 7
+ { lat: 239, common_pid: 2041 } hitcount: 1
+ { lat: 239, common_pid: 2043 } hitcount: 11
+ { lat: 239, common_pid: 2037 } hitcount: 11
+ { lat: 239, common_pid: 2038 } hitcount: 6
+ { lat: 239, common_pid: 2036 } hitcount: 7
+ { lat: 239, common_pid: 2040 } hitcount: 1
+ { lat: 239, common_pid: 2042 } hitcount: 9
+ { lat: 240, common_pid: 2037 } hitcount: 29
+ { lat: 240, common_pid: 2043 } hitcount: 15
+ { lat: 240, common_pid: 2040 } hitcount: 44
+ { lat: 240, common_pid: 2039 } hitcount: 1
+ { lat: 240, common_pid: 2041 } hitcount: 2
+ { lat: 240, common_pid: 2038 } hitcount: 1
+ { lat: 240, common_pid: 2036 } hitcount: 10
+ { lat: 240, common_pid: 2042 } hitcount: 13
+ { lat: 241, common_pid: 2036 } hitcount: 21
+ { lat: 241, common_pid: 2041 } hitcount: 36
+ { lat: 241, common_pid: 2037 } hitcount: 34
+ { lat: 241, common_pid: 2042 } hitcount: 14
+ { lat: 241, common_pid: 2040 } hitcount: 94
+ { lat: 241, common_pid: 2039 } hitcount: 12
+ { lat: 241, common_pid: 2038 } hitcount: 2
+ { lat: 241, common_pid: 2043 } hitcount: 28
+ { lat: 242, common_pid: 2040 } hitcount: 109
+ { lat: 242, common_pid: 2041 } hitcount: 506
+ { lat: 242, common_pid: 2039 } hitcount: 155
+ { lat: 242, common_pid: 2042 } hitcount: 21
+ { lat: 242, common_pid: 2037 } hitcount: 52
+ { lat: 242, common_pid: 2043 } hitcount: 21
+ { lat: 242, common_pid: 2036 } hitcount: 16
+ { lat: 242, common_pid: 2038 } hitcount: 156
+ { lat: 243, common_pid: 2037 } hitcount: 46
+ { lat: 243, common_pid: 2039 } hitcount: 40
+ { lat: 243, common_pid: 2042 } hitcount: 119
+ { lat: 243, common_pid: 2041 } hitcount: 611
+ { lat: 243, common_pid: 2036 } hitcount: 69
+ { lat: 243, common_pid: 2038 } hitcount: 784
+ { lat: 243, common_pid: 2040 } hitcount: 323
+ { lat: 243, common_pid: 2043 } hitcount: 14
+ { lat: 244, common_pid: 2043 } hitcount: 35
+ { lat: 244, common_pid: 2042 } hitcount: 305
+ { lat: 244, common_pid: 2039 } hitcount: 8
+ { lat: 244, common_pid: 2040 } hitcount: 4515
+ { lat: 244, common_pid: 2038 } hitcount: 371
+ { lat: 244, common_pid: 2037 } hitcount: 31
+ { lat: 244, common_pid: 2036 } hitcount: 114
+ { lat: 244, common_pid: 2041 } hitcount: 3396
+ { lat: 245, common_pid: 2036 } hitcount: 700
+ { lat: 245, common_pid: 2041 } hitcount: 2772
+ { lat: 245, common_pid: 2037 } hitcount: 268
+ { lat: 245, common_pid: 2039 } hitcount: 472
+ { lat: 245, common_pid: 2038 } hitcount: 2758
+ { lat: 245, common_pid: 2042 } hitcount: 3833
+ { lat: 245, common_pid: 2040 } hitcount: 3105
+ { lat: 245, common_pid: 2043 } hitcount: 645
+ { lat: 246, common_pid: 2038 } hitcount: 3451
+ { lat: 246, common_pid: 2041 } hitcount: 142
+ { lat: 246, common_pid: 2037 } hitcount: 5101
+ { lat: 246, common_pid: 2040 } hitcount: 68
+ { lat: 246, common_pid: 2043 } hitcount: 5099
+ { lat: 246, common_pid: 2039 } hitcount: 5608
+ { lat: 246, common_pid: 2042 } hitcount: 3723
+ { lat: 246, common_pid: 2036 } hitcount: 4738
+ { lat: 247, common_pid: 2042 } hitcount: 312
+ { lat: 247, common_pid: 2043 } hitcount: 2385
+ { lat: 247, common_pid: 2041 } hitcount: 452
+ { lat: 247, common_pid: 2038 } hitcount: 792
+ { lat: 247, common_pid: 2040 } hitcount: 78
+ { lat: 247, common_pid: 2036 } hitcount: 2375
+ { lat: 247, common_pid: 2039 } hitcount: 1834
+ { lat: 247, common_pid: 2037 } hitcount: 2655
+ { lat: 248, common_pid: 2037 } hitcount: 36
+ { lat: 248, common_pid: 2042 } hitcount: 11
+ { lat: 248, common_pid: 2038 } hitcount: 122
+ { lat: 248, common_pid: 2036 } hitcount: 135
+ { lat: 248, common_pid: 2039 } hitcount: 26
+ { lat: 248, common_pid: 2041 } hitcount: 503
+ { lat: 248, common_pid: 2043 } hitcount: 66
+ { lat: 248, common_pid: 2040 } hitcount: 46
+ { lat: 249, common_pid: 2037 } hitcount: 29
+ { lat: 249, common_pid: 2038 } hitcount: 1
+ { lat: 249, common_pid: 2043 } hitcount: 29
+ { lat: 249, common_pid: 2039 } hitcount: 8
+ { lat: 249, common_pid: 2042 } hitcount: 56
+ { lat: 249, common_pid: 2040 } hitcount: 27
+ { lat: 249, common_pid: 2041 } hitcount: 11
+ { lat: 249, common_pid: 2036 } hitcount: 27
+ { lat: 250, common_pid: 2038 } hitcount: 1
+ { lat: 250, common_pid: 2036 } hitcount: 30
+ { lat: 250, common_pid: 2040 } hitcount: 19
+ { lat: 250, common_pid: 2043 } hitcount: 22
+ { lat: 250, common_pid: 2042 } hitcount: 20
+ { lat: 250, common_pid: 2041 } hitcount: 1
+ { lat: 250, common_pid: 2039 } hitcount: 6
+ { lat: 250, common_pid: 2037 } hitcount: 48
+ { lat: 251, common_pid: 2037 } hitcount: 43
+ { lat: 251, common_pid: 2039 } hitcount: 1
+ { lat: 251, common_pid: 2036 } hitcount: 12
+ { lat: 251, common_pid: 2042 } hitcount: 2
+ { lat: 251, common_pid: 2041 } hitcount: 1
+ { lat: 251, common_pid: 2043 } hitcount: 15
+ { lat: 251, common_pid: 2040 } hitcount: 3
+ { lat: 252, common_pid: 2040 } hitcount: 1
+ { lat: 252, common_pid: 2036 } hitcount: 12
+ { lat: 252, common_pid: 2037 } hitcount: 21
+ { lat: 252, common_pid: 2043 } hitcount: 14
+ { lat: 253, common_pid: 2037 } hitcount: 21
+ { lat: 253, common_pid: 2039 } hitcount: 2
+ { lat: 253, common_pid: 2036 } hitcount: 9
+ { lat: 253, common_pid: 2043 } hitcount: 6
+ { lat: 253, common_pid: 2040 } hitcount: 1
+ { lat: 254, common_pid: 2036 } hitcount: 8
+ { lat: 254, common_pid: 2043 } hitcount: 3
+ { lat: 254, common_pid: 2041 } hitcount: 1
+ { lat: 254, common_pid: 2042 } hitcount: 1
+ { lat: 254, common_pid: 2039 } hitcount: 1
+ { lat: 254, common_pid: 2037 } hitcount: 12
+ { lat: 255, common_pid: 2043 } hitcount: 1
+ { lat: 255, common_pid: 2037 } hitcount: 2
+ { lat: 255, common_pid: 2036 } hitcount: 2
+ { lat: 255, common_pid: 2039 } hitcount: 8
+ { lat: 256, common_pid: 2043 } hitcount: 1
+ { lat: 256, common_pid: 2036 } hitcount: 4
+ { lat: 256, common_pid: 2039 } hitcount: 6
+ { lat: 257, common_pid: 2039 } hitcount: 5
+ { lat: 257, common_pid: 2036 } hitcount: 4
+ { lat: 258, common_pid: 2039 } hitcount: 5
+ { lat: 258, common_pid: 2036 } hitcount: 2
+ { lat: 259, common_pid: 2036 } hitcount: 7
+ { lat: 259, common_pid: 2039 } hitcount: 7
+ { lat: 260, common_pid: 2036 } hitcount: 8
+ { lat: 260, common_pid: 2039 } hitcount: 6
+ { lat: 261, common_pid: 2036 } hitcount: 5
+ { lat: 261, common_pid: 2039 } hitcount: 7
+ { lat: 262, common_pid: 2039 } hitcount: 5
+ { lat: 262, common_pid: 2036 } hitcount: 5
+ { lat: 263, common_pid: 2039 } hitcount: 7
+ { lat: 263, common_pid: 2036 } hitcount: 7
+ { lat: 264, common_pid: 2039 } hitcount: 9
+ { lat: 264, common_pid: 2036 } hitcount: 9
+ { lat: 265, common_pid: 2036 } hitcount: 5
+ { lat: 265, common_pid: 2039 } hitcount: 1
+ { lat: 266, common_pid: 2036 } hitcount: 1
+ { lat: 266, common_pid: 2039 } hitcount: 3
+ { lat: 267, common_pid: 2036 } hitcount: 1
+ { lat: 267, common_pid: 2039 } hitcount: 3
+ { lat: 268, common_pid: 2036 } hitcount: 1
+ { lat: 268, common_pid: 2039 } hitcount: 6
+ { lat: 269, common_pid: 2036 } hitcount: 1
+ { lat: 269, common_pid: 2043 } hitcount: 1
+ { lat: 269, common_pid: 2039 } hitcount: 2
+ { lat: 270, common_pid: 2040 } hitcount: 1
+ { lat: 270, common_pid: 2039 } hitcount: 6
+ { lat: 271, common_pid: 2041 } hitcount: 1
+ { lat: 271, common_pid: 2039 } hitcount: 5
+ { lat: 272, common_pid: 2039 } hitcount: 10
+ { lat: 273, common_pid: 2039 } hitcount: 8
+ { lat: 274, common_pid: 2039 } hitcount: 2
+ { lat: 275, common_pid: 2039 } hitcount: 1
+ { lat: 276, common_pid: 2039 } hitcount: 2
+ { lat: 276, common_pid: 2037 } hitcount: 1
+ { lat: 276, common_pid: 2038 } hitcount: 1
+ { lat: 277, common_pid: 2039 } hitcount: 1
+ { lat: 277, common_pid: 2042 } hitcount: 1
+ { lat: 278, common_pid: 2039 } hitcount: 1
+ { lat: 279, common_pid: 2039 } hitcount: 4
+ { lat: 279, common_pid: 2043 } hitcount: 1
+ { lat: 280, common_pid: 2039 } hitcount: 3
+ { lat: 283, common_pid: 2036 } hitcount: 2
+ { lat: 284, common_pid: 2039 } hitcount: 1
+ { lat: 284, common_pid: 2043 } hitcount: 1
+ { lat: 288, common_pid: 2039 } hitcount: 1
+ { lat: 289, common_pid: 2039 } hitcount: 1
+ { lat: 300, common_pid: 2039 } hitcount: 1
+ { lat: 384, common_pid: 2039 } hitcount: 1
+
+ Totals:
+ Hits: 67625
+ Entries: 278
+ Dropped: 0
+
+Note, the writes are around the sleep, so ideally they will all be of 250
+microseconds. If you are wondering how there are several that are under
+250 microseconds, that is because the way cyclictest works, is if one
+iteration comes in late, the next one will set the timer to wake up less that
+250. That is, if an iteration came in 50 microseconds late, the next wake up
+will be at 200 microseconds.
+
+But this could easily be done in userspace. To make this even more
+interesting, we can mix the histogram between events that happened in the
+kernel with trace_marker::
+
+ # cd /sys/kernel/tracing
+ # echo 'latency u64 lat' > synthetic_events
+ # echo 'hist:keys=pid:ts0=common_timestamp.usecs' > events/sched/sched_waking/trigger
+ # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(sched.sched_waking).latency($lat) if buf == "end"' > events/ftrace/print/trigger
+ # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger
+
+The difference this time is that instead of using the trace_marker to start
+the latency, the sched_waking event is used, matching the common_pid for the
+trace_marker write with the pid that is being woken by sched_waking.
+
+After running cyclictest again with the same parameters, we now have::
+
+ # cat events/synthetic/latency/hist
+ # event histogram
+ #
+ # trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active]
+ #
+
+ { lat: 7, common_pid: 2302 } hitcount: 640
+ { lat: 7, common_pid: 2299 } hitcount: 42
+ { lat: 7, common_pid: 2303 } hitcount: 18
+ { lat: 7, common_pid: 2305 } hitcount: 166
+ { lat: 7, common_pid: 2306 } hitcount: 1
+ { lat: 7, common_pid: 2301 } hitcount: 91
+ { lat: 7, common_pid: 2300 } hitcount: 17
+ { lat: 8, common_pid: 2303 } hitcount: 8296
+ { lat: 8, common_pid: 2304 } hitcount: 6864
+ { lat: 8, common_pid: 2305 } hitcount: 9464
+ { lat: 8, common_pid: 2301 } hitcount: 9213
+ { lat: 8, common_pid: 2306 } hitcount: 6246
+ { lat: 8, common_pid: 2302 } hitcount: 8797
+ { lat: 8, common_pid: 2299 } hitcount: 8771
+ { lat: 8, common_pid: 2300 } hitcount: 8119
+ { lat: 9, common_pid: 2305 } hitcount: 1519
+ { lat: 9, common_pid: 2299 } hitcount: 2346
+ { lat: 9, common_pid: 2303 } hitcount: 2841
+ { lat: 9, common_pid: 2301 } hitcount: 1846
+ { lat: 9, common_pid: 2304 } hitcount: 3861
+ { lat: 9, common_pid: 2302 } hitcount: 1210
+ { lat: 9, common_pid: 2300 } hitcount: 2762
+ { lat: 9, common_pid: 2306 } hitcount: 4247
+ { lat: 10, common_pid: 2299 } hitcount: 16
+ { lat: 10, common_pid: 2306 } hitcount: 333
+ { lat: 10, common_pid: 2303 } hitcount: 16
+ { lat: 10, common_pid: 2304 } hitcount: 168
+ { lat: 10, common_pid: 2302 } hitcount: 240
+ { lat: 10, common_pid: 2301 } hitcount: 28
+ { lat: 10, common_pid: 2300 } hitcount: 95
+ { lat: 10, common_pid: 2305 } hitcount: 18
+ { lat: 11, common_pid: 2303 } hitcount: 5
+ { lat: 11, common_pid: 2305 } hitcount: 8
+ { lat: 11, common_pid: 2306 } hitcount: 221
+ { lat: 11, common_pid: 2302 } hitcount: 76
+ { lat: 11, common_pid: 2304 } hitcount: 26
+ { lat: 11, common_pid: 2300 } hitcount: 125
+ { lat: 11, common_pid: 2299 } hitcount: 2
+ { lat: 12, common_pid: 2305 } hitcount: 3
+ { lat: 12, common_pid: 2300 } hitcount: 6
+ { lat: 12, common_pid: 2306 } hitcount: 90
+ { lat: 12, common_pid: 2302 } hitcount: 4
+ { lat: 12, common_pid: 2303 } hitcount: 1
+ { lat: 12, common_pid: 2304 } hitcount: 122
+ { lat: 13, common_pid: 2300 } hitcount: 12
+ { lat: 13, common_pid: 2301 } hitcount: 1
+ { lat: 13, common_pid: 2306 } hitcount: 32
+ { lat: 13, common_pid: 2302 } hitcount: 5
+ { lat: 13, common_pid: 2305 } hitcount: 1
+ { lat: 13, common_pid: 2303 } hitcount: 1
+ { lat: 13, common_pid: 2304 } hitcount: 61
+ { lat: 14, common_pid: 2303 } hitcount: 4
+ { lat: 14, common_pid: 2306 } hitcount: 5
+ { lat: 14, common_pid: 2305 } hitcount: 4
+ { lat: 14, common_pid: 2304 } hitcount: 62
+ { lat: 14, common_pid: 2302 } hitcount: 19
+ { lat: 14, common_pid: 2300 } hitcount: 33
+ { lat: 14, common_pid: 2299 } hitcount: 1
+ { lat: 14, common_pid: 2301 } hitcount: 4
+ { lat: 15, common_pid: 2305 } hitcount: 1
+ { lat: 15, common_pid: 2302 } hitcount: 25
+ { lat: 15, common_pid: 2300 } hitcount: 11
+ { lat: 15, common_pid: 2299 } hitcount: 5
+ { lat: 15, common_pid: 2301 } hitcount: 1
+ { lat: 15, common_pid: 2304 } hitcount: 8
+ { lat: 15, common_pid: 2303 } hitcount: 1
+ { lat: 15, common_pid: 2306 } hitcount: 6
+ { lat: 16, common_pid: 2302 } hitcount: 31
+ { lat: 16, common_pid: 2306 } hitcount: 3
+ { lat: 16, common_pid: 2300 } hitcount: 5
+ { lat: 17, common_pid: 2302 } hitcount: 6
+ { lat: 17, common_pid: 2303 } hitcount: 1
+ { lat: 18, common_pid: 2304 } hitcount: 1
+ { lat: 18, common_pid: 2302 } hitcount: 8
+ { lat: 18, common_pid: 2299 } hitcount: 1
+ { lat: 18, common_pid: 2301 } hitcount: 1
+ { lat: 19, common_pid: 2303 } hitcount: 4
+ { lat: 19, common_pid: 2304 } hitcount: 5
+ { lat: 19, common_pid: 2302 } hitcount: 4
+ { lat: 19, common_pid: 2299 } hitcount: 3
+ { lat: 19, common_pid: 2306 } hitcount: 1
+ { lat: 19, common_pid: 2300 } hitcount: 4
+ { lat: 19, common_pid: 2305 } hitcount: 5
+ { lat: 20, common_pid: 2299 } hitcount: 2
+ { lat: 20, common_pid: 2302 } hitcount: 3
+ { lat: 20, common_pid: 2305 } hitcount: 1
+ { lat: 20, common_pid: 2300 } hitcount: 2
+ { lat: 20, common_pid: 2301 } hitcount: 2
+ { lat: 20, common_pid: 2303 } hitcount: 3
+ { lat: 21, common_pid: 2305 } hitcount: 1
+ { lat: 21, common_pid: 2299 } hitcount: 5
+ { lat: 21, common_pid: 2303 } hitcount: 4
+ { lat: 21, common_pid: 2302 } hitcount: 7
+ { lat: 21, common_pid: 2300 } hitcount: 1
+ { lat: 21, common_pid: 2301 } hitcount: 5
+ { lat: 21, common_pid: 2304 } hitcount: 2
+ { lat: 22, common_pid: 2302 } hitcount: 5
+ { lat: 22, common_pid: 2303 } hitcount: 1
+ { lat: 22, common_pid: 2306 } hitcount: 3
+ { lat: 22, common_pid: 2301 } hitcount: 2
+ { lat: 22, common_pid: 2300 } hitcount: 1
+ { lat: 22, common_pid: 2299 } hitcount: 1
+ { lat: 22, common_pid: 2305 } hitcount: 1
+ { lat: 22, common_pid: 2304 } hitcount: 1
+ { lat: 23, common_pid: 2299 } hitcount: 1
+ { lat: 23, common_pid: 2306 } hitcount: 2
+ { lat: 23, common_pid: 2302 } hitcount: 6
+ { lat: 24, common_pid: 2302 } hitcount: 3
+ { lat: 24, common_pid: 2300 } hitcount: 1
+ { lat: 24, common_pid: 2306 } hitcount: 2
+ { lat: 24, common_pid: 2305 } hitcount: 1
+ { lat: 24, common_pid: 2299 } hitcount: 1
+ { lat: 25, common_pid: 2300 } hitcount: 1
+ { lat: 25, common_pid: 2302 } hitcount: 4
+ { lat: 26, common_pid: 2302 } hitcount: 2
+ { lat: 27, common_pid: 2305 } hitcount: 1
+ { lat: 27, common_pid: 2300 } hitcount: 1
+ { lat: 27, common_pid: 2302 } hitcount: 3
+ { lat: 28, common_pid: 2306 } hitcount: 1
+ { lat: 28, common_pid: 2302 } hitcount: 4
+ { lat: 29, common_pid: 2302 } hitcount: 1
+ { lat: 29, common_pid: 2300 } hitcount: 2
+ { lat: 29, common_pid: 2306 } hitcount: 1
+ { lat: 29, common_pid: 2304 } hitcount: 1
+ { lat: 30, common_pid: 2302 } hitcount: 4
+ { lat: 31, common_pid: 2302 } hitcount: 6
+ { lat: 32, common_pid: 2302 } hitcount: 1
+ { lat: 33, common_pid: 2299 } hitcount: 1
+ { lat: 33, common_pid: 2302 } hitcount: 3
+ { lat: 34, common_pid: 2302 } hitcount: 2
+ { lat: 35, common_pid: 2302 } hitcount: 1
+ { lat: 35, common_pid: 2304 } hitcount: 1
+ { lat: 36, common_pid: 2302 } hitcount: 4
+ { lat: 37, common_pid: 2302 } hitcount: 6
+ { lat: 38, common_pid: 2302 } hitcount: 2
+ { lat: 39, common_pid: 2302 } hitcount: 2
+ { lat: 39, common_pid: 2304 } hitcount: 1
+ { lat: 40, common_pid: 2304 } hitcount: 2
+ { lat: 40, common_pid: 2302 } hitcount: 5
+ { lat: 41, common_pid: 2304 } hitcount: 1
+ { lat: 41, common_pid: 2302 } hitcount: 8
+ { lat: 42, common_pid: 2302 } hitcount: 6
+ { lat: 42, common_pid: 2304 } hitcount: 1
+ { lat: 43, common_pid: 2302 } hitcount: 3
+ { lat: 43, common_pid: 2304 } hitcount: 4
+ { lat: 44, common_pid: 2302 } hitcount: 6
+ { lat: 45, common_pid: 2302 } hitcount: 5
+ { lat: 46, common_pid: 2302 } hitcount: 5
+ { lat: 47, common_pid: 2302 } hitcount: 7
+ { lat: 48, common_pid: 2301 } hitcount: 1
+ { lat: 48, common_pid: 2302 } hitcount: 9
+ { lat: 49, common_pid: 2302 } hitcount: 3
+ { lat: 50, common_pid: 2302 } hitcount: 1
+ { lat: 50, common_pid: 2301 } hitcount: 1
+ { lat: 51, common_pid: 2302 } hitcount: 2
+ { lat: 51, common_pid: 2301 } hitcount: 1
+ { lat: 61, common_pid: 2302 } hitcount: 1
+ { lat: 110, common_pid: 2302 } hitcount: 1
+
+ Totals:
+ Hits: 89565
+ Entries: 158
+ Dropped: 0
+
+This doesn't tell us any information about how late cyclictest may have
+woken up, but it does show us a nice histogram of how long it took from
+the time that cyclictest was woken to the time it made it into user space.
+++ /dev/null
- Event Histograms
-
- Documentation written by Tom Zanussi
-
-1. Introduction
-===============
-
- Histogram triggers are special event triggers that can be used to
- aggregate trace event data into histograms. For information on
- trace events and event triggers, see Documentation/trace/events.rst.
-
-
-2. Histogram Trigger Command
-============================
-
- A histogram trigger command is an event trigger command that
- aggregates event hits into a hash table keyed on one or more trace
- event format fields (or stacktrace) and a set of running totals
- derived from one or more trace event format fields and/or event
- counts (hitcount).
-
- The format of a hist trigger is as follows:
-
- hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>]
- [:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue]
- [:clear][:name=histname1] [if <filter>]
-
- When a matching event is hit, an entry is added to a hash table
- using the key(s) and value(s) named. Keys and values correspond to
- fields in the event's format description. Values must correspond to
- numeric fields - on an event hit, the value(s) will be added to a
- sum kept for that field. The special string 'hitcount' can be used
- in place of an explicit value field - this is simply a count of
- event hits. If 'values' isn't specified, an implicit 'hitcount'
- value will be automatically created and used as the only value.
- Keys can be any field, or the special string 'stacktrace', which
- will use the event's kernel stacktrace as the key. The keywords
- 'keys' or 'key' can be used to specify keys, and the keywords
- 'values', 'vals', or 'val' can be used to specify values. Compound
- keys consisting of up to two fields can be specified by the 'keys'
- keyword. Hashing a compound key produces a unique entry in the
- table for each unique combination of component keys, and can be
- useful for providing more fine-grained summaries of event data.
- Additionally, sort keys consisting of up to two fields can be
- specified by the 'sort' keyword. If more than one field is
- specified, the result will be a 'sort within a sort': the first key
- is taken to be the primary sort key and the second the secondary
- key. If a hist trigger is given a name using the 'name' parameter,
- its histogram data will be shared with other triggers of the same
- name, and trigger hits will update this common data. Only triggers
- with 'compatible' fields can be combined in this way; triggers are
- 'compatible' if the fields named in the trigger share the same
- number and type of fields and those fields also have the same names.
- Note that any two events always share the compatible 'hitcount' and
- 'stacktrace' fields and can therefore be combined using those
- fields, however pointless that may be.
-
- 'hist' triggers add a 'hist' file to each event's subdirectory.
- Reading the 'hist' file for the event will dump the hash table in
- its entirety to stdout. If there are multiple hist triggers
- attached to an event, there will be a table for each trigger in the
- output. The table displayed for a named trigger will be the same as
- any other instance having the same name. Each printed hash table
- entry is a simple list of the keys and values comprising the entry;
- keys are printed first and are delineated by curly braces, and are
- followed by the set of value fields for the entry. By default,
- numeric fields are displayed as base-10 integers. This can be
- modified by appending any of the following modifiers to the field
- name:
-
- .hex display a number as a hex value
- .sym display an address as a symbol
- .sym-offset display an address as a symbol and offset
- .syscall display a syscall id as a system call name
- .execname display a common_pid as a program name
- .log2 display log2 value rather than raw number
- .usecs display a common_timestamp in microseconds
-
- Note that in general the semantics of a given field aren't
- interpreted when applying a modifier to it, but there are some
- restrictions to be aware of in this regard:
-
- - only the 'hex' modifier can be used for values (because values
- are essentially sums, and the other modifiers don't make sense
- in that context).
- - the 'execname' modifier can only be used on a 'common_pid'. The
- reason for this is that the execname is simply the 'comm' value
- saved for the 'current' process when an event was triggered,
- which is the same as the common_pid value saved by the event
- tracing code. Trying to apply that comm value to other pid
- values wouldn't be correct, and typically events that care save
- pid-specific comm fields in the event itself.
-
- A typical usage scenario would be the following to enable a hist
- trigger, read its current contents, and then turn it off:
-
- # echo 'hist:keys=skbaddr.hex:vals=len' > \
- /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
- # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
-
- # echo '!hist:keys=skbaddr.hex:vals=len' > \
- /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
- The trigger file itself can be read to show the details of the
- currently attached hist trigger. This information is also displayed
- at the top of the 'hist' file when read.
-
- By default, the size of the hash table is 2048 entries. The 'size'
- parameter can be used to specify more or fewer than that. The units
- are in terms of hashtable entries - if a run uses more entries than
- specified, the results will show the number of 'drops', the number
- of hits that were ignored. The size should be a power of 2 between
- 128 and 131072 (any non- power-of-2 number specified will be rounded
- up).
-
- The 'sort' parameter can be used to specify a value field to sort
- on. The default if unspecified is 'hitcount' and the default sort
- order is 'ascending'. To sort in the opposite direction, append
- .descending' to the sort key.
-
- The 'pause' parameter can be used to pause an existing hist trigger
- or to start a hist trigger but not log any events until told to do
- so. 'continue' or 'cont' can be used to start or restart a paused
- hist trigger.
-
- The 'clear' parameter will clear the contents of a running hist
- trigger and leave its current paused/active state.
-
- Note that the 'pause', 'cont', and 'clear' parameters should be
- applied using 'append' shell operator ('>>') if applied to an
- existing trigger, rather than via the '>' operator, which will cause
- the trigger to be removed through truncation.
-
-- enable_hist/disable_hist
-
- The enable_hist and disable_hist triggers can be used to have one
- event conditionally start and stop another event's already-attached
- hist trigger. Any number of enable_hist and disable_hist triggers
- can be attached to a given event, allowing that event to kick off
- and stop aggregations on a host of other events.
-
- The format is very similar to the enable/disable_event triggers:
-
- enable_hist:<system>:<event>[:count]
- disable_hist:<system>:<event>[:count]
-
- Instead of enabling or disabling the tracing of the target event
- into the trace buffer as the enable/disable_event triggers do, the
- enable/disable_hist triggers enable or disable the aggregation of
- the target event into a hash table.
-
- A typical usage scenario for the enable_hist/disable_hist triggers
- would be to first set up a paused hist trigger on some event,
- followed by an enable_hist/disable_hist pair that turns the hist
- aggregation on and off when conditions of interest are hit:
-
- # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
- # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
-
- # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
-
- The above sets up an initially paused hist trigger which is unpaused
- and starts aggregating events when a given program is executed, and
- which stops aggregating when the process exits and the hist trigger
- is paused again.
-
- The examples below provide a more concrete illustration of the
- concepts and typical usage patterns discussed above.
-
- 'special' event fields
- ------------------------
-
- There are a number of 'special event fields' available for use as
- keys or values in a hist trigger. These look like and behave as if
- they were actual event fields, but aren't really part of the event's
- field definition or format file. They are however available for any
- event, and can be used anywhere an actual event field could be.
- They are:
-
- common_timestamp u64 - timestamp (from ring buffer) associated
- with the event, in nanoseconds. May be
- modified by .usecs to have timestamps
- interpreted as microseconds.
- cpu int - the cpu on which the event occurred.
-
- Extended error information
- --------------------------
-
- For some error conditions encountered when invoking a hist trigger
- command, extended error information is available via the
- corresponding event's 'hist' file. Reading the hist file after an
- error will display more detailed information about what went wrong,
- if information is available. This extended error information will
- be available until the next hist trigger command for that event.
-
- If available for a given error condition, the extended error
- information and usage takes the following form:
-
- # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
- echo: write error: Invalid argument
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/hist
- ERROR: Couldn't yyy: zzz
- Last command: xxx
-
-6.2 'hist' trigger examples
----------------------------
-
- The first set of examples creates aggregations using the kmalloc
- event. The fields that can be used for the hist trigger are listed
- in the kmalloc event's format file:
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/format
- name: kmalloc
- ID: 374
- format:
- field:unsigned short common_type; offset:0; size:2; signed:0;
- field:unsigned char common_flags; offset:2; size:1; signed:0;
- field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
- field:int common_pid; offset:4; size:4; signed:1;
-
- field:unsigned long call_site; offset:8; size:8; signed:0;
- field:const void * ptr; offset:16; size:8; signed:0;
- field:size_t bytes_req; offset:24; size:8; signed:0;
- field:size_t bytes_alloc; offset:32; size:8; signed:0;
- field:gfp_t gfp_flags; offset:40; size:4; signed:0;
-
- We'll start by creating a hist trigger that generates a simple table
- that lists the total number of bytes requested for each function in
- the kernel that made one or more calls to kmalloc:
-
- # echo 'hist:key=call_site:val=bytes_req' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- This tells the tracing system to create a 'hist' trigger using the
- call_site field of the kmalloc event as the key for the table, which
- just means that each unique call_site address will have an entry
- created for it in the table. The 'val=bytes_req' parameter tells
- the hist trigger that for each unique entry (call_site) in the
- table, it should keep a running total of the number of bytes
- requested by that call_site.
-
- We'll let it run for awhile and then dump the contents of the 'hist'
- file in the kmalloc event's subdirectory (for readability, a number
- of entries have been omitted):
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
-
- { call_site: 18446744072106379007 } hitcount: 1 bytes_req: 176
- { call_site: 18446744071579557049 } hitcount: 1 bytes_req: 1024
- { call_site: 18446744071580608289 } hitcount: 1 bytes_req: 16384
- { call_site: 18446744071581827654 } hitcount: 1 bytes_req: 24
- { call_site: 18446744071580700980 } hitcount: 1 bytes_req: 8
- { call_site: 18446744071579359876 } hitcount: 1 bytes_req: 152
- { call_site: 18446744071580795365 } hitcount: 3 bytes_req: 144
- { call_site: 18446744071581303129 } hitcount: 3 bytes_req: 144
- { call_site: 18446744071580713234 } hitcount: 4 bytes_req: 2560
- { call_site: 18446744071580933750 } hitcount: 4 bytes_req: 736
- .
- .
- .
- { call_site: 18446744072106047046 } hitcount: 69 bytes_req: 5576
- { call_site: 18446744071582116407 } hitcount: 73 bytes_req: 2336
- { call_site: 18446744072106054684 } hitcount: 136 bytes_req: 140504
- { call_site: 18446744072106224230 } hitcount: 136 bytes_req: 19584
- { call_site: 18446744072106078074 } hitcount: 153 bytes_req: 2448
- { call_site: 18446744072106062406 } hitcount: 153 bytes_req: 36720
- { call_site: 18446744071582507929 } hitcount: 153 bytes_req: 37088
- { call_site: 18446744072102520590 } hitcount: 273 bytes_req: 10920
- { call_site: 18446744071582143559 } hitcount: 358 bytes_req: 716
- { call_site: 18446744072106465852 } hitcount: 417 bytes_req: 56712
- { call_site: 18446744072102523378 } hitcount: 485 bytes_req: 27160
- { call_site: 18446744072099568646 } hitcount: 1676 bytes_req: 33520
-
- Totals:
- Hits: 4610
- Entries: 45
- Dropped: 0
-
- The output displays a line for each entry, beginning with the key
- specified in the trigger, followed by the value(s) also specified in
- the trigger. At the beginning of the output is a line that displays
- the trigger info, which can also be displayed by reading the
- 'trigger' file:
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
- hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
-
- At the end of the output are a few lines that display the overall
- totals for the run. The 'Hits' field shows the total number of
- times the event trigger was hit, the 'Entries' field shows the total
- number of used entries in the hash table, and the 'Dropped' field
- shows the number of hits that were dropped because the number of
- used entries for the run exceeded the maximum number of entries
- allowed for the table (normally 0, but if not a hint that you may
- want to increase the size of the table using the 'size' parameter).
-
- Notice in the above output that there's an extra field, 'hitcount',
- which wasn't specified in the trigger. Also notice that in the
- trigger info output, there's a parameter, 'sort=hitcount', which
- wasn't specified in the trigger either. The reason for that is that
- every trigger implicitly keeps a count of the total number of hits
- attributed to a given entry, called the 'hitcount'. That hitcount
- information is explicitly displayed in the output, and in the
- absence of a user-specified sort parameter, is used as the default
- sort field.
-
- The value 'hitcount' can be used in place of an explicit value in
- the 'values' parameter if you don't really need to have any
- particular field summed and are mainly interested in hit
- frequencies.
-
- To turn the hist trigger off, simply call up the trigger in the
- command history and re-execute it with a '!' prepended:
-
- # echo '!hist:key=call_site:val=bytes_req' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- Finally, notice that the call_site as displayed in the output above
- isn't really very useful. It's an address, but normally addresses
- are displayed in hex. To have a numeric field displayed as a hex
- value, simply append '.hex' to the field name in the trigger:
-
- # echo 'hist:key=call_site.hex:val=bytes_req' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site.hex:vals=bytes_req:sort=hitcount:size=2048 [active]
-
- { call_site: ffffffffa026b291 } hitcount: 1 bytes_req: 433
- { call_site: ffffffffa07186ff } hitcount: 1 bytes_req: 176
- { call_site: ffffffff811ae721 } hitcount: 1 bytes_req: 16384
- { call_site: ffffffff811c5134 } hitcount: 1 bytes_req: 8
- { call_site: ffffffffa04a9ebb } hitcount: 1 bytes_req: 511
- { call_site: ffffffff8122e0a6 } hitcount: 1 bytes_req: 12
- { call_site: ffffffff8107da84 } hitcount: 1 bytes_req: 152
- { call_site: ffffffff812d8246 } hitcount: 1 bytes_req: 24
- { call_site: ffffffff811dc1e5 } hitcount: 3 bytes_req: 144
- { call_site: ffffffffa02515e8 } hitcount: 3 bytes_req: 648
- { call_site: ffffffff81258159 } hitcount: 3 bytes_req: 144
- { call_site: ffffffff811c80f4 } hitcount: 4 bytes_req: 544
- .
- .
- .
- { call_site: ffffffffa06c7646 } hitcount: 106 bytes_req: 8024
- { call_site: ffffffffa06cb246 } hitcount: 132 bytes_req: 31680
- { call_site: ffffffffa06cef7a } hitcount: 132 bytes_req: 2112
- { call_site: ffffffff8137e399 } hitcount: 132 bytes_req: 23232
- { call_site: ffffffffa06c941c } hitcount: 185 bytes_req: 171360
- { call_site: ffffffffa06f2a66 } hitcount: 185 bytes_req: 26640
- { call_site: ffffffffa036a70e } hitcount: 265 bytes_req: 10600
- { call_site: ffffffff81325447 } hitcount: 292 bytes_req: 584
- { call_site: ffffffffa072da3c } hitcount: 446 bytes_req: 60656
- { call_site: ffffffffa036b1f2 } hitcount: 526 bytes_req: 29456
- { call_site: ffffffffa0099c06 } hitcount: 1780 bytes_req: 35600
-
- Totals:
- Hits: 4775
- Entries: 46
- Dropped: 0
-
- Even that's only marginally more useful - while hex values do look
- more like addresses, what users are typically more interested in
- when looking at text addresses are the corresponding symbols
- instead. To have an address displayed as symbolic value instead,
- simply append '.sym' or '.sym-offset' to the field name in the
- trigger:
-
- # echo 'hist:key=call_site.sym:val=bytes_req' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=hitcount:size=2048 [active]
-
- { call_site: [ffffffff810adcb9] syslog_print_all } hitcount: 1 bytes_req: 1024
- { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
- { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
- { call_site: [ffffffff8154acbe] usb_alloc_urb } hitcount: 1 bytes_req: 192
- { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
- { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
- { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
- { call_site: [ffffffff811febd5] fsnotify_alloc_group } hitcount: 2 bytes_req: 528
- { call_site: [ffffffff81440f58] __tty_buffer_request_room } hitcount: 2 bytes_req: 2624
- { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 2 bytes_req: 96
- { call_site: [ffffffffa05e19af] ieee80211_start_tx_ba_session [mac80211] } hitcount: 2 bytes_req: 464
- { call_site: [ffffffff81672406] tcp_get_metrics } hitcount: 2 bytes_req: 304
- { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
- { call_site: [ffffffff81089b05] sched_create_group } hitcount: 2 bytes_req: 1424
- .
- .
- .
- { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1185 bytes_req: 123240
- { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 1185 bytes_req: 104280
- { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 1402 bytes_req: 190672
- { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 1518 bytes_req: 146208
- { call_site: [ffffffffa029070e] drm_vma_node_allow [drm] } hitcount: 1746 bytes_req: 69840
- { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 2021 bytes_req: 792312
- { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 2592 bytes_req: 145152
- { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2629 bytes_req: 378576
- { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2629 bytes_req: 3783248
- { call_site: [ffffffff81325607] apparmor_file_alloc_security } hitcount: 5192 bytes_req: 10384
- { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 5529 bytes_req: 110584
- { call_site: [ffffffff8131ebf7] aa_alloc_task_context } hitcount: 21943 bytes_req: 702176
- { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 55759 bytes_req: 5074265
-
- Totals:
- Hits: 109928
- Entries: 71
- Dropped: 0
-
- Because the default sort key above is 'hitcount', the above shows a
- the list of call_sites by increasing hitcount, so that at the bottom
- we see the functions that made the most kmalloc calls during the
- run. If instead we we wanted to see the top kmalloc callers in
- terms of the number of bytes requested rather than the number of
- calls, and we wanted the top caller to appear at the top, we can use
- the 'sort' parameter, along with the 'descending' modifier:
-
- # echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
-
- { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2186 bytes_req: 3397464
- { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1790 bytes_req: 712176
- { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 8132 bytes_req: 513135
- { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 106 bytes_req: 440128
- { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2186 bytes_req: 314784
- { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 2174 bytes_req: 208992
- { call_site: [ffffffff811ae8e1] __kmalloc } hitcount: 8 bytes_req: 131072
- { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 859 bytes_req: 116824
- { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 1834 bytes_req: 102704
- { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 972 bytes_req: 101088
- { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 972 bytes_req: 85536
- { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 3333 bytes_req: 66664
- { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 209 bytes_req: 61632
- .
- .
- .
- { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
- { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
- { call_site: [ffffffff812d8406] copy_semundo } hitcount: 2 bytes_req: 48
- { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 1 bytes_req: 48
- { call_site: [ffffffffa027121a] drm_getmagic [drm] } hitcount: 1 bytes_req: 48
- { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
- { call_site: [ffffffff811c52f4] bprm_change_interp } hitcount: 2 bytes_req: 16
- { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
- { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
- { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
-
- Totals:
- Hits: 32133
- Entries: 81
- Dropped: 0
-
- To display the offset and size information in addition to the symbol
- name, just use 'sym-offset' instead:
-
- # echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site.sym-offset:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
-
- { call_site: [ffffffffa046041c] i915_gem_execbuffer2+0x6c/0x2c0 [i915] } hitcount: 4569 bytes_req: 3163720
- { call_site: [ffffffffa0489a66] intel_ring_begin+0xc6/0x1f0 [i915] } hitcount: 4569 bytes_req: 657936
- { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23+0x694/0x1020 [i915] } hitcount: 1519 bytes_req: 472936
- { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23+0x516/0x1020 [i915] } hitcount: 3050 bytes_req: 211832
- { call_site: [ffffffff811e2a1b] seq_buf_alloc+0x1b/0x50 } hitcount: 34 bytes_req: 148384
- { call_site: [ffffffffa04a580c] intel_crtc_page_flip+0xbc/0x870 [i915] } hitcount: 1385 bytes_req: 144040
- { call_site: [ffffffff811ae8e1] __kmalloc+0x191/0x1b0 } hitcount: 8 bytes_req: 131072
- { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl+0x282/0x360 [drm] } hitcount: 1385 bytes_req: 121880
- { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc+0x32/0x100 [drm] } hitcount: 1848 bytes_req: 103488
- { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state+0x2c/0xa0 [i915] } hitcount: 461 bytes_req: 62696
- { call_site: [ffffffffa029070e] drm_vma_node_allow+0x2e/0xd0 [drm] } hitcount: 1541 bytes_req: 61640
- { call_site: [ffffffff815f8d7b] sk_prot_alloc+0xcb/0x1b0 } hitcount: 57 bytes_req: 57456
- .
- .
- .
- { call_site: [ffffffff8109524a] alloc_fair_sched_group+0x5a/0x1a0 } hitcount: 2 bytes_req: 128
- { call_site: [ffffffffa027b921] drm_vm_open_locked+0x31/0xa0 [drm] } hitcount: 3 bytes_req: 96
- { call_site: [ffffffff8122e266] proc_self_follow_link+0x76/0xb0 } hitcount: 8 bytes_req: 96
- { call_site: [ffffffff81213e80] load_elf_binary+0x240/0x1650 } hitcount: 3 bytes_req: 84
- { call_site: [ffffffff8154bc62] usb_control_msg+0x42/0x110 } hitcount: 1 bytes_req: 8
- { call_site: [ffffffffa00bf6fe] hidraw_send_report+0x7e/0x1a0 [hid] } hitcount: 1 bytes_req: 7
- { call_site: [ffffffffa00bf1ca] hidraw_report_event+0x8a/0x120 [hid] } hitcount: 1 bytes_req: 7
-
- Totals:
- Hits: 26098
- Entries: 64
- Dropped: 0
-
- We can also add multiple fields to the 'values' parameter. For
- example, we might want to see the total number of bytes allocated
- alongside bytes requested, and display the result sorted by bytes
- allocated in a descending order:
-
- # echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site.sym:vals=bytes_req,bytes_alloc:sort=bytes_alloc.descending:size=2048 [active]
-
- { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 7403 bytes_req: 4084360 bytes_alloc: 5958016
- { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 541 bytes_req: 2213968 bytes_alloc: 2228224
- { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 7404 bytes_req: 1066176 bytes_alloc: 1421568
- { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1565 bytes_req: 557368 bytes_alloc: 1037760
- { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 9557 bytes_req: 595778 bytes_alloc: 695744
- { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 5839 bytes_req: 430680 bytes_alloc: 470400
- { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 2388 bytes_req: 324768 bytes_alloc: 458496
- { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 3911 bytes_req: 219016 bytes_alloc: 250304
- { call_site: [ffffffff815f8d7b] sk_prot_alloc } hitcount: 235 bytes_req: 236880 bytes_alloc: 240640
- { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 557 bytes_req: 169024 bytes_alloc: 221760
- { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 9378 bytes_req: 187548 bytes_alloc: 206312
- { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1519 bytes_req: 157976 bytes_alloc: 194432
- .
- .
- .
- { call_site: [ffffffff8109bd3b] sched_autogroup_create_attach } hitcount: 2 bytes_req: 144 bytes_alloc: 192
- { call_site: [ffffffff81097ee8] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
- { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
- { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
- { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
- { call_site: [ffffffff81213e80] load_elf_binary } hitcount: 3 bytes_req: 84 bytes_alloc: 96
- { call_site: [ffffffff81079a2e] kthread_create_on_node } hitcount: 1 bytes_req: 56 bytes_alloc: 64
- { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
- { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 bytes_alloc: 8
- { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
-
- Totals:
- Hits: 66598
- Entries: 65
- Dropped: 0
-
- Finally, to finish off our kmalloc example, instead of simply having
- the hist trigger display symbolic call_sites, we can have the hist
- trigger additionally display the complete set of kernel stack traces
- that led to each call_site. To do that, we simply use the special
- value 'stacktrace' for the key parameter:
-
- # echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- The above trigger will use the kernel stack trace in effect when an
- event is triggered as the key for the hash table. This allows the
- enumeration of every kernel callpath that led up to a particular
- event, along with a running total of any of the event fields for
- that event. Here we tally bytes requested and bytes allocated for
- every callpath in the system that led up to a kmalloc (in this case
- every callpath to a kmalloc for a kernel compile):
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active]
-
- { stacktrace:
- __kmalloc_track_caller+0x10b/0x1a0
- kmemdup+0x20/0x50
- hidraw_report_event+0x8a/0x120 [hid]
- hid_report_raw_event+0x3ea/0x440 [hid]
- hid_input_report+0x112/0x190 [hid]
- hid_irq_in+0xc2/0x260 [usbhid]
- __usb_hcd_giveback_urb+0x72/0x120
- usb_giveback_urb_bh+0x9e/0xe0
- tasklet_hi_action+0xf8/0x100
- __do_softirq+0x114/0x2c0
- irq_exit+0xa5/0xb0
- do_IRQ+0x5a/0xf0
- ret_from_intr+0x0/0x30
- cpuidle_enter+0x17/0x20
- cpu_startup_entry+0x315/0x3e0
- rest_init+0x7c/0x80
- } hitcount: 3 bytes_req: 21 bytes_alloc: 24
- { stacktrace:
- __kmalloc_track_caller+0x10b/0x1a0
- kmemdup+0x20/0x50
- hidraw_report_event+0x8a/0x120 [hid]
- hid_report_raw_event+0x3ea/0x440 [hid]
- hid_input_report+0x112/0x190 [hid]
- hid_irq_in+0xc2/0x260 [usbhid]
- __usb_hcd_giveback_urb+0x72/0x120
- usb_giveback_urb_bh+0x9e/0xe0
- tasklet_hi_action+0xf8/0x100
- __do_softirq+0x114/0x2c0
- irq_exit+0xa5/0xb0
- do_IRQ+0x5a/0xf0
- ret_from_intr+0x0/0x30
- } hitcount: 3 bytes_req: 21 bytes_alloc: 24
- { stacktrace:
- kmem_cache_alloc_trace+0xeb/0x150
- aa_alloc_task_context+0x27/0x40
- apparmor_cred_prepare+0x1f/0x50
- security_prepare_creds+0x16/0x20
- prepare_creds+0xdf/0x1a0
- SyS_capset+0xb5/0x200
- system_call_fastpath+0x12/0x6a
- } hitcount: 1 bytes_req: 32 bytes_alloc: 32
- .
- .
- .
- { stacktrace:
- __kmalloc+0x11b/0x1b0
- i915_gem_execbuffer2+0x6c/0x2c0 [i915]
- drm_ioctl+0x349/0x670 [drm]
- do_vfs_ioctl+0x2f0/0x4f0
- SyS_ioctl+0x81/0xa0
- system_call_fastpath+0x12/0x6a
- } hitcount: 17726 bytes_req: 13944120 bytes_alloc: 19593808
- { stacktrace:
- __kmalloc+0x11b/0x1b0
- load_elf_phdrs+0x76/0xa0
- load_elf_binary+0x102/0x1650
- search_binary_handler+0x97/0x1d0
- do_execveat_common.isra.34+0x551/0x6e0
- SyS_execve+0x3a/0x50
- return_from_execve+0x0/0x23
- } hitcount: 33348 bytes_req: 17152128 bytes_alloc: 20226048
- { stacktrace:
- kmem_cache_alloc_trace+0xeb/0x150
- apparmor_file_alloc_security+0x27/0x40
- security_file_alloc+0x16/0x20
- get_empty_filp+0x93/0x1c0
- path_openat+0x31/0x5f0
- do_filp_open+0x3a/0x90
- do_sys_open+0x128/0x220
- SyS_open+0x1e/0x20
- system_call_fastpath+0x12/0x6a
- } hitcount: 4766422 bytes_req: 9532844 bytes_alloc: 38131376
- { stacktrace:
- __kmalloc+0x11b/0x1b0
- seq_buf_alloc+0x1b/0x50
- seq_read+0x2cc/0x370
- proc_reg_read+0x3d/0x80
- __vfs_read+0x28/0xe0
- vfs_read+0x86/0x140
- SyS_read+0x46/0xb0
- system_call_fastpath+0x12/0x6a
- } hitcount: 19133 bytes_req: 78368768 bytes_alloc: 78368768
-
- Totals:
- Hits: 6085872
- Entries: 253
- Dropped: 0
-
- If you key a hist trigger on common_pid, in order for example to
- gather and display sorted totals for each process, you can use the
- special .execname modifier to display the executable names for the
- processes in the table rather than raw pids. The example below
- keeps a per-process sum of total bytes read:
-
- # echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \
- /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
-
- # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/hist
- # trigger info: hist:keys=common_pid.execname:vals=count:sort=count.descending:size=2048 [active]
-
- { common_pid: gnome-terminal [ 3196] } hitcount: 280 count: 1093512
- { common_pid: Xorg [ 1309] } hitcount: 525 count: 256640
- { common_pid: compiz [ 2889] } hitcount: 59 count: 254400
- { common_pid: bash [ 8710] } hitcount: 3 count: 66369
- { common_pid: dbus-daemon-lau [ 8703] } hitcount: 49 count: 47739
- { common_pid: irqbalance [ 1252] } hitcount: 27 count: 27648
- { common_pid: 01ifupdown [ 8705] } hitcount: 3 count: 17216
- { common_pid: dbus-daemon [ 772] } hitcount: 10 count: 12396
- { common_pid: Socket Thread [ 8342] } hitcount: 11 count: 11264
- { common_pid: nm-dhcp-client. [ 8701] } hitcount: 6 count: 7424
- { common_pid: gmain [ 1315] } hitcount: 18 count: 6336
- .
- .
- .
- { common_pid: postgres [ 1892] } hitcount: 2 count: 32
- { common_pid: postgres [ 1891] } hitcount: 2 count: 32
- { common_pid: gmain [ 8704] } hitcount: 2 count: 32
- { common_pid: upstart-dbus-br [ 2740] } hitcount: 21 count: 21
- { common_pid: nm-dispatcher.a [ 8696] } hitcount: 1 count: 16
- { common_pid: indicator-datet [ 2904] } hitcount: 1 count: 16
- { common_pid: gdbus [ 2998] } hitcount: 1 count: 16
- { common_pid: rtkit-daemon [ 2052] } hitcount: 1 count: 8
- { common_pid: init [ 1] } hitcount: 2 count: 2
-
- Totals:
- Hits: 2116
- Entries: 51
- Dropped: 0
-
- Similarly, if you key a hist trigger on syscall id, for example to
- gather and display a list of systemwide syscall hits, you can use
- the special .syscall modifier to display the syscall names rather
- than raw ids. The example below keeps a running total of syscall
- counts for the system during the run:
-
- # echo 'hist:key=id.syscall:val=hitcount' > \
- /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
-
- # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
- # trigger info: hist:keys=id.syscall:vals=hitcount:sort=hitcount:size=2048 [active]
-
- { id: sys_fsync [ 74] } hitcount: 1
- { id: sys_newuname [ 63] } hitcount: 1
- { id: sys_prctl [157] } hitcount: 1
- { id: sys_statfs [137] } hitcount: 1
- { id: sys_symlink [ 88] } hitcount: 1
- { id: sys_sendmmsg [307] } hitcount: 1
- { id: sys_semctl [ 66] } hitcount: 1
- { id: sys_readlink [ 89] } hitcount: 3
- { id: sys_bind [ 49] } hitcount: 3
- { id: sys_getsockname [ 51] } hitcount: 3
- { id: sys_unlink [ 87] } hitcount: 3
- { id: sys_rename [ 82] } hitcount: 4
- { id: unknown_syscall [ 58] } hitcount: 4
- { id: sys_connect [ 42] } hitcount: 4
- { id: sys_getpid [ 39] } hitcount: 4
- .
- .
- .
- { id: sys_rt_sigprocmask [ 14] } hitcount: 952
- { id: sys_futex [202] } hitcount: 1534
- { id: sys_write [ 1] } hitcount: 2689
- { id: sys_setitimer [ 38] } hitcount: 2797
- { id: sys_read [ 0] } hitcount: 3202
- { id: sys_select [ 23] } hitcount: 3773
- { id: sys_writev [ 20] } hitcount: 4531
- { id: sys_poll [ 7] } hitcount: 8314
- { id: sys_recvmsg [ 47] } hitcount: 13738
- { id: sys_ioctl [ 16] } hitcount: 21843
-
- Totals:
- Hits: 67612
- Entries: 72
- Dropped: 0
-
- The syscall counts above provide a rough overall picture of system
- call activity on the system; we can see for example that the most
- popular system call on this system was the 'sys_ioctl' system call.
-
- We can use 'compound' keys to refine that number and provide some
- further insight as to which processes exactly contribute to the
- overall ioctl count.
-
- The command below keeps a hitcount for every unique combination of
- system call id and pid - the end result is essentially a table
- that keeps a per-pid sum of system call hits. The results are
- sorted using the system call id as the primary key, and the
- hitcount sum as the secondary key:
-
- # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \
- /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
-
- # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
- # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active]
-
- { id: sys_read [ 0], common_pid: rtkit-daemon [ 1877] } hitcount: 1
- { id: sys_read [ 0], common_pid: gdbus [ 2976] } hitcount: 1
- { id: sys_read [ 0], common_pid: console-kit-dae [ 3400] } hitcount: 1
- { id: sys_read [ 0], common_pid: postgres [ 1865] } hitcount: 1
- { id: sys_read [ 0], common_pid: deja-dup-monito [ 3543] } hitcount: 2
- { id: sys_read [ 0], common_pid: NetworkManager [ 890] } hitcount: 2
- { id: sys_read [ 0], common_pid: evolution-calen [ 3048] } hitcount: 2
- { id: sys_read [ 0], common_pid: postgres [ 1864] } hitcount: 2
- { id: sys_read [ 0], common_pid: nm-applet [ 3022] } hitcount: 2
- { id: sys_read [ 0], common_pid: whoopsie [ 1212] } hitcount: 2
- .
- .
- .
- { id: sys_ioctl [ 16], common_pid: bash [ 8479] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: bash [ 3472] } hitcount: 12
- { id: sys_ioctl [ 16], common_pid: gnome-terminal [ 3199] } hitcount: 16
- { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 1808
- { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 5580
- .
- .
- .
- { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2690] } hitcount: 3
- { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2688] } hitcount: 16
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 975] } hitcount: 2
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 3204] } hitcount: 4
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 2888] } hitcount: 4
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 3003] } hitcount: 4
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 2873] } hitcount: 4
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 3196] } hitcount: 6
- { id: sys_openat [257], common_pid: java [ 2623] } hitcount: 2
- { id: sys_eventfd2 [290], common_pid: ibus-ui-gtk3 [ 2760] } hitcount: 4
- { id: sys_eventfd2 [290], common_pid: compiz [ 2994] } hitcount: 6
-
- Totals:
- Hits: 31536
- Entries: 323
- Dropped: 0
-
- The above list does give us a breakdown of the ioctl syscall by
- pid, but it also gives us quite a bit more than that, which we
- don't really care about at the moment. Since we know the syscall
- id for sys_ioctl (16, displayed next to the sys_ioctl name), we
- can use that to filter out all the other syscalls:
-
- # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \
- /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
-
- # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
- # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active]
-
- { id: sys_ioctl [ 16], common_pid: gmain [ 2769] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: evolution-addre [ 8571] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: gmain [ 3003] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: gmain [ 2781] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: gmain [ 2829] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: bash [ 8726] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: bash [ 8508] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: gmain [ 2970] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: gmain [ 2768] } hitcount: 1
- .
- .
- .
- { id: sys_ioctl [ 16], common_pid: pool [ 8559] } hitcount: 45
- { id: sys_ioctl [ 16], common_pid: pool [ 8555] } hitcount: 48
- { id: sys_ioctl [ 16], common_pid: pool [ 8551] } hitcount: 48
- { id: sys_ioctl [ 16], common_pid: avahi-daemon [ 896] } hitcount: 66
- { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 26674
- { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 73443
-
- Totals:
- Hits: 101162
- Entries: 103
- Dropped: 0
-
- The above output shows that 'compiz' and 'Xorg' are far and away
- the heaviest ioctl callers (which might lead to questions about
- whether they really need to be making all those calls and to
- possible avenues for further investigation.)
-
- The compound key examples used a key and a sum value (hitcount) to
- sort the output, but we can just as easily use two keys instead.
- Here's an example where we use a compound key composed of the the
- common_pid and size event fields. Sorting with pid as the primary
- key and 'size' as the secondary key allows us to display an
- ordered summary of the recvfrom sizes, with counts, received by
- each process:
-
- # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \
- /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger
-
- # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist
- # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active]
-
- { common_pid: smbd [ 784], size: 4 } hitcount: 1
- { common_pid: dnsmasq [ 1412], size: 4096 } hitcount: 672
- { common_pid: postgres [ 1796], size: 1000 } hitcount: 6
- { common_pid: postgres [ 1867], size: 1000 } hitcount: 10
- { common_pid: bamfdaemon [ 2787], size: 28 } hitcount: 2
- { common_pid: bamfdaemon [ 2787], size: 14360 } hitcount: 1
- { common_pid: compiz [ 2994], size: 8 } hitcount: 1
- { common_pid: compiz [ 2994], size: 20 } hitcount: 11
- { common_pid: gnome-terminal [ 3199], size: 4 } hitcount: 2
- { common_pid: firefox [ 8817], size: 4 } hitcount: 1
- { common_pid: firefox [ 8817], size: 8 } hitcount: 5
- { common_pid: firefox [ 8817], size: 588 } hitcount: 2
- { common_pid: firefox [ 8817], size: 628 } hitcount: 1
- { common_pid: firefox [ 8817], size: 6944 } hitcount: 1
- { common_pid: firefox [ 8817], size: 408880 } hitcount: 2
- { common_pid: firefox [ 8822], size: 8 } hitcount: 2
- { common_pid: firefox [ 8822], size: 160 } hitcount: 2
- { common_pid: firefox [ 8822], size: 320 } hitcount: 2
- { common_pid: firefox [ 8822], size: 352 } hitcount: 1
- .
- .
- .
- { common_pid: pool [ 8923], size: 1960 } hitcount: 10
- { common_pid: pool [ 8923], size: 2048 } hitcount: 10
- { common_pid: pool [ 8924], size: 1960 } hitcount: 10
- { common_pid: pool [ 8924], size: 2048 } hitcount: 10
- { common_pid: pool [ 8928], size: 1964 } hitcount: 4
- { common_pid: pool [ 8928], size: 1965 } hitcount: 2
- { common_pid: pool [ 8928], size: 2048 } hitcount: 6
- { common_pid: pool [ 8929], size: 1982 } hitcount: 1
- { common_pid: pool [ 8929], size: 2048 } hitcount: 1
-
- Totals:
- Hits: 2016
- Entries: 224
- Dropped: 0
-
- The above example also illustrates the fact that although a compound
- key is treated as a single entity for hashing purposes, the sub-keys
- it's composed of can be accessed independently.
-
- The next example uses a string field as the hash key and
- demonstrates how you can manually pause and continue a hist trigger.
- In this example, we'll aggregate fork counts and don't expect a
- large number of entries in the hash table, so we'll drop it to a
- much smaller number, say 256:
-
- # echo 'hist:key=child_comm:val=hitcount:size=256' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
- # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
-
- { child_comm: dconf worker } hitcount: 1
- { child_comm: ibus-daemon } hitcount: 1
- { child_comm: whoopsie } hitcount: 1
- { child_comm: smbd } hitcount: 1
- { child_comm: gdbus } hitcount: 1
- { child_comm: kthreadd } hitcount: 1
- { child_comm: dconf worker } hitcount: 1
- { child_comm: evolution-alarm } hitcount: 2
- { child_comm: Socket Thread } hitcount: 2
- { child_comm: postgres } hitcount: 2
- { child_comm: bash } hitcount: 3
- { child_comm: compiz } hitcount: 3
- { child_comm: evolution-sourc } hitcount: 4
- { child_comm: dhclient } hitcount: 4
- { child_comm: pool } hitcount: 5
- { child_comm: nm-dispatcher.a } hitcount: 8
- { child_comm: firefox } hitcount: 8
- { child_comm: dbus-daemon } hitcount: 8
- { child_comm: glib-pacrunner } hitcount: 10
- { child_comm: evolution } hitcount: 23
-
- Totals:
- Hits: 89
- Entries: 20
- Dropped: 0
-
- If we want to pause the hist trigger, we can simply append :pause to
- the command that started the trigger. Notice that the trigger info
- displays as [paused]:
-
- # echo 'hist:key=child_comm:val=hitcount:size=256:pause' >> \
- /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
- # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [paused]
-
- { child_comm: dconf worker } hitcount: 1
- { child_comm: kthreadd } hitcount: 1
- { child_comm: dconf worker } hitcount: 1
- { child_comm: gdbus } hitcount: 1
- { child_comm: ibus-daemon } hitcount: 1
- { child_comm: Socket Thread } hitcount: 2
- { child_comm: evolution-alarm } hitcount: 2
- { child_comm: smbd } hitcount: 2
- { child_comm: bash } hitcount: 3
- { child_comm: whoopsie } hitcount: 3
- { child_comm: compiz } hitcount: 3
- { child_comm: evolution-sourc } hitcount: 4
- { child_comm: pool } hitcount: 5
- { child_comm: postgres } hitcount: 6
- { child_comm: firefox } hitcount: 8
- { child_comm: dhclient } hitcount: 10
- { child_comm: emacs } hitcount: 12
- { child_comm: dbus-daemon } hitcount: 20
- { child_comm: nm-dispatcher.a } hitcount: 20
- { child_comm: evolution } hitcount: 35
- { child_comm: glib-pacrunner } hitcount: 59
-
- Totals:
- Hits: 199
- Entries: 21
- Dropped: 0
-
- To manually continue having the trigger aggregate events, append
- :cont instead. Notice that the trigger info displays as [active]
- again, and the data has changed:
-
- # echo 'hist:key=child_comm:val=hitcount:size=256:cont' >> \
- /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
- # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
-
- { child_comm: dconf worker } hitcount: 1
- { child_comm: dconf worker } hitcount: 1
- { child_comm: kthreadd } hitcount: 1
- { child_comm: gdbus } hitcount: 1
- { child_comm: ibus-daemon } hitcount: 1
- { child_comm: Socket Thread } hitcount: 2
- { child_comm: evolution-alarm } hitcount: 2
- { child_comm: smbd } hitcount: 2
- { child_comm: whoopsie } hitcount: 3
- { child_comm: compiz } hitcount: 3
- { child_comm: evolution-sourc } hitcount: 4
- { child_comm: bash } hitcount: 5
- { child_comm: pool } hitcount: 5
- { child_comm: postgres } hitcount: 6
- { child_comm: firefox } hitcount: 8
- { child_comm: dhclient } hitcount: 11
- { child_comm: emacs } hitcount: 12
- { child_comm: dbus-daemon } hitcount: 22
- { child_comm: nm-dispatcher.a } hitcount: 22
- { child_comm: evolution } hitcount: 35
- { child_comm: glib-pacrunner } hitcount: 59
-
- Totals:
- Hits: 206
- Entries: 21
- Dropped: 0
-
- The previous example showed how to start and stop a hist trigger by
- appending 'pause' and 'continue' to the hist trigger command. A
- hist trigger can also be started in a paused state by initially
- starting the trigger with ':pause' appended. This allows you to
- start the trigger only when you're ready to start collecting data
- and not before. For example, you could start the trigger in a
- paused state, then unpause it and do something you want to measure,
- then pause the trigger again when done.
-
- Of course, doing this manually can be difficult and error-prone, but
- it is possible to automatically start and stop a hist trigger based
- on some condition, via the enable_hist and disable_hist triggers.
-
- For example, suppose we wanted to take a look at the relative
- weights in terms of skb length for each callpath that leads to a
- netif_receieve_skb event when downloading a decent-sized file using
- wget.
-
- First we set up an initially paused stacktrace trigger on the
- netif_receive_skb event:
-
- # echo 'hist:key=stacktrace:vals=len:pause' > \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
- Next, we set up an 'enable_hist' trigger on the sched_process_exec
- event, with an 'if filename==/usr/bin/wget' filter. The effect of
- this new trigger is that it will 'unpause' the hist trigger we just
- set up on netif_receive_skb if and only if it sees a
- sched_process_exec event with a filename of '/usr/bin/wget'. When
- that happens, all netif_receive_skb events are aggregated into a
- hash table keyed on stacktrace:
-
- # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
-
- The aggregation continues until the netif_receive_skb is paused
- again, which is what the following disable_hist event does by
- creating a similar setup on the sched_process_exit event, using the
- filter 'comm==wget':
-
- # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
-
- Whenever a process exits and the comm field of the disable_hist
- trigger filter matches 'comm==wget', the netif_receive_skb hist
- trigger is disabled.
-
- The overall effect is that netif_receive_skb events are aggregated
- into the hash table for only the duration of the wget. Executing a
- wget command and then listing the 'hist' file will display the
- output generated by the wget command:
-
- $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
-
- # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
- # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
-
- { stacktrace:
- __netif_receive_skb_core+0x46d/0x990
- __netif_receive_skb+0x18/0x60
- netif_receive_skb_internal+0x23/0x90
- napi_gro_receive+0xc8/0x100
- ieee80211_deliver_skb+0xd6/0x270 [mac80211]
- ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
- ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
- ieee80211_rx+0x31d/0x900 [mac80211]
- iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
- iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
- iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
- irq_thread_fn+0x20/0x50
- irq_thread+0x11f/0x150
- kthread+0xd2/0xf0
- ret_from_fork+0x42/0x70
- } hitcount: 85 len: 28884
- { stacktrace:
- __netif_receive_skb_core+0x46d/0x990
- __netif_receive_skb+0x18/0x60
- netif_receive_skb_internal+0x23/0x90
- napi_gro_complete+0xa4/0xe0
- dev_gro_receive+0x23a/0x360
- napi_gro_receive+0x30/0x100
- ieee80211_deliver_skb+0xd6/0x270 [mac80211]
- ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
- ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
- ieee80211_rx+0x31d/0x900 [mac80211]
- iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
- iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
- iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
- irq_thread_fn+0x20/0x50
- irq_thread+0x11f/0x150
- kthread+0xd2/0xf0
- } hitcount: 98 len: 664329
- { stacktrace:
- __netif_receive_skb_core+0x46d/0x990
- __netif_receive_skb+0x18/0x60
- process_backlog+0xa8/0x150
- net_rx_action+0x15d/0x340
- __do_softirq+0x114/0x2c0
- do_softirq_own_stack+0x1c/0x30
- do_softirq+0x65/0x70
- __local_bh_enable_ip+0xb5/0xc0
- ip_finish_output+0x1f4/0x840
- ip_output+0x6b/0xc0
- ip_local_out_sk+0x31/0x40
- ip_send_skb+0x1a/0x50
- udp_send_skb+0x173/0x2a0
- udp_sendmsg+0x2bf/0x9f0
- inet_sendmsg+0x64/0xa0
- sock_sendmsg+0x3d/0x50
- } hitcount: 115 len: 13030
- { stacktrace:
- __netif_receive_skb_core+0x46d/0x990
- __netif_receive_skb+0x18/0x60
- netif_receive_skb_internal+0x23/0x90
- napi_gro_complete+0xa4/0xe0
- napi_gro_flush+0x6d/0x90
- iwl_pcie_irq_handler+0x92a/0x12f0 [iwlwifi]
- irq_thread_fn+0x20/0x50
- irq_thread+0x11f/0x150
- kthread+0xd2/0xf0
- ret_from_fork+0x42/0x70
- } hitcount: 934 len: 5512212
-
- Totals:
- Hits: 1232
- Entries: 4
- Dropped: 0
-
- The above shows all the netif_receive_skb callpaths and their total
- lengths for the duration of the wget command.
-
- The 'clear' hist trigger param can be used to clear the hash table.
- Suppose we wanted to try another run of the previous example but
- this time also wanted to see the complete list of events that went
- into the histogram. In order to avoid having to set everything up
- again, we can just clear the histogram first:
-
- # echo 'hist:key=stacktrace:vals=len:clear' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
- Just to verify that it is in fact cleared, here's what we now see in
- the hist file:
-
- # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
- # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
-
- Totals:
- Hits: 0
- Entries: 0
- Dropped: 0
-
- Since we want to see the detailed list of every netif_receive_skb
- event occurring during the new run, which are in fact the same
- events being aggregated into the hash table, we add some additional
- 'enable_event' events to the triggering sched_process_exec and
- sched_process_exit events as such:
-
- # echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
-
- # echo 'disable_event:net:netif_receive_skb if comm==wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
-
- If you read the trigger files for the sched_process_exec and
- sched_process_exit triggers, you should see two triggers for each:
- one enabling/disabling the hist aggregation and the other
- enabling/disabling the logging of events:
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
- enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
- enable_hist:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
- enable_event:net:netif_receive_skb:unlimited if comm==wget
- disable_hist:net:netif_receive_skb:unlimited if comm==wget
-
- In other words, whenever either of the sched_process_exec or
- sched_process_exit events is hit and matches 'wget', it enables or
- disables both the histogram and the event log, and what you end up
- with is a hash table and set of events just covering the specified
- duration. Run the wget command again:
-
- $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
-
- Displaying the 'hist' file should show something similar to what you
- saw in the last run, but this time you should also see the
- individual events in the trace file:
-
- # cat /sys/kernel/debug/tracing/trace
-
- # tracer: nop
- #
- # entries-in-buffer/entries-written: 183/1426 #P:4
- #
- # _-----=> irqs-off
- # / _----=> need-resched
- # | / _---=> hardirq/softirq
- # || / _--=> preempt-depth
- # ||| / delay
- # TASK-PID CPU# |||| TIMESTAMP FUNCTION
- # | | | |||| | |
- wget-15108 [000] ..s1 31769.606929: netif_receive_skb: dev=lo skbaddr=ffff88009c353100 len=60
- wget-15108 [000] ..s1 31769.606999: netif_receive_skb: dev=lo skbaddr=ffff88009c353200 len=60
- dnsmasq-1382 [000] ..s1 31769.677652: netif_receive_skb: dev=lo skbaddr=ffff88009c352b00 len=130
- dnsmasq-1382 [000] ..s1 31769.685917: netif_receive_skb: dev=lo skbaddr=ffff88009c352200 len=138
- ##### CPU 2 buffer started ####
- irq/29-iwlwifi-559 [002] ..s. 31772.031529: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433d00 len=2948
- irq/29-iwlwifi-559 [002] ..s. 31772.031572: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432200 len=1500
- irq/29-iwlwifi-559 [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948
- irq/29-iwlwifi-559 [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948
- irq/29-iwlwifi-559 [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500
- .
- .
- .
-
- The following example demonstrates how multiple hist triggers can be
- attached to a given event. This capability can be useful for
- creating a set of different summaries derived from the same set of
- events, or for comparing the effects of different filters, among
- other things.
-
- # echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
- # echo 'hist:keys=skbaddr.hex:vals=len if len > 4096' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
- # echo 'hist:keys=skbaddr.hex:vals=len if len == 256' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
- # echo 'hist:keys=skbaddr.hex:vals=len' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
- # echo 'hist:keys=len:vals=common_preempt_count' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
- The above set of commands create four triggers differing only in
- their filters, along with a completely different though fairly
- nonsensical trigger. Note that in order to append multiple hist
- triggers to the same file, you should use the '>>' operator to
- append them ('>' will also add the new hist trigger, but will remove
- any existing hist triggers beforehand).
-
- Displaying the contents of the 'hist' file for the event shows the
- contents of all five histograms:
-
- # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
-
- # event histogram
- #
- # trigger info: hist:keys=len:vals=hitcount,common_preempt_count:sort=hitcount:size=2048 [active]
- #
-
- { len: 176 } hitcount: 1 common_preempt_count: 0
- { len: 223 } hitcount: 1 common_preempt_count: 0
- { len: 4854 } hitcount: 1 common_preempt_count: 0
- { len: 395 } hitcount: 1 common_preempt_count: 0
- { len: 177 } hitcount: 1 common_preempt_count: 0
- { len: 446 } hitcount: 1 common_preempt_count: 0
- { len: 1601 } hitcount: 1 common_preempt_count: 0
- .
- .
- .
- { len: 1280 } hitcount: 66 common_preempt_count: 0
- { len: 116 } hitcount: 81 common_preempt_count: 40
- { len: 708 } hitcount: 112 common_preempt_count: 0
- { len: 46 } hitcount: 221 common_preempt_count: 0
- { len: 1264 } hitcount: 458 common_preempt_count: 0
-
- Totals:
- Hits: 1428
- Entries: 147
- Dropped: 0
-
-
- # event histogram
- #
- # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
- #
-
- { skbaddr: ffff8800baee5e00 } hitcount: 1 len: 130
- { skbaddr: ffff88005f3d5600 } hitcount: 1 len: 1280
- { skbaddr: ffff88005f3d4900 } hitcount: 1 len: 1280
- { skbaddr: ffff88009fed6300 } hitcount: 1 len: 115
- { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 115
- { skbaddr: ffff88008cdb1900 } hitcount: 1 len: 46
- { skbaddr: ffff880064b5ef00 } hitcount: 1 len: 118
- { skbaddr: ffff880044e3c700 } hitcount: 1 len: 60
- { skbaddr: ffff880100065900 } hitcount: 1 len: 46
- { skbaddr: ffff8800d46bd500 } hitcount: 1 len: 116
- { skbaddr: ffff88005f3d5f00 } hitcount: 1 len: 1280
- { skbaddr: ffff880100064700 } hitcount: 1 len: 365
- { skbaddr: ffff8800badb6f00 } hitcount: 1 len: 60
- .
- .
- .
- { skbaddr: ffff88009fe0be00 } hitcount: 27 len: 24677
- { skbaddr: ffff88009fe0a400 } hitcount: 27 len: 23052
- { skbaddr: ffff88009fe0b700 } hitcount: 31 len: 25589
- { skbaddr: ffff88009fe0b600 } hitcount: 32 len: 27326
- { skbaddr: ffff88006a462800 } hitcount: 68 len: 71678
- { skbaddr: ffff88006a463700 } hitcount: 70 len: 72678
- { skbaddr: ffff88006a462b00 } hitcount: 71 len: 77589
- { skbaddr: ffff88006a463600 } hitcount: 73 len: 71307
- { skbaddr: ffff88006a462200 } hitcount: 81 len: 81032
-
- Totals:
- Hits: 1451
- Entries: 318
- Dropped: 0
-
-
- # event histogram
- #
- # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len == 256 [active]
- #
-
-
- Totals:
- Hits: 0
- Entries: 0
- Dropped: 0
-
-
- # event histogram
- #
- # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len > 4096 [active]
- #
-
- { skbaddr: ffff88009fd2c300 } hitcount: 1 len: 7212
- { skbaddr: ffff8800d2bcce00 } hitcount: 1 len: 7212
- { skbaddr: ffff8800d2bcd700 } hitcount: 1 len: 7212
- { skbaddr: ffff8800d2bcda00 } hitcount: 1 len: 21492
- { skbaddr: ffff8800ae2e2d00 } hitcount: 1 len: 7212
- { skbaddr: ffff8800d2bcdb00 } hitcount: 1 len: 7212
- { skbaddr: ffff88006a4df500 } hitcount: 1 len: 4854
- { skbaddr: ffff88008ce47b00 } hitcount: 1 len: 18636
- { skbaddr: ffff8800ae2e2200 } hitcount: 1 len: 12924
- { skbaddr: ffff88005f3e1000 } hitcount: 1 len: 4356
- { skbaddr: ffff8800d2bcdc00 } hitcount: 2 len: 24420
- { skbaddr: ffff8800d2bcc200 } hitcount: 2 len: 12996
-
- Totals:
- Hits: 14
- Entries: 12
- Dropped: 0
-
-
- # event histogram
- #
- # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len < 0 [active]
- #
-
-
- Totals:
- Hits: 0
- Entries: 0
- Dropped: 0
-
- Named triggers can be used to have triggers share a common set of
- histogram data. This capability is mostly useful for combining the
- output of events generated by tracepoints contained inside inline
- functions, but names can be used in a hist trigger on any event.
- For example, these two triggers when hit will update the same 'len'
- field in the shared 'foo' histogram data:
-
- # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
- # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
- /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
- You can see that they're updating common histogram data by reading
- each event's hist files at the same time:
-
- # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist;
- cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
-
- # event histogram
- #
- # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
- #
-
- { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46
- { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76
- { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468
- { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46
- { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52
- { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168
- { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260
- { skbaddr: ffff880064505000 } hitcount: 1 len: 46
- { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32
- { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46
- { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44
- { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168
- { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40
- { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40
- { skbaddr: ffff880064505f00 } hitcount: 1 len: 174
- { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160
- { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76
- { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32
- { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988
- { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46
- { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44
- { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676
- { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107
- { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92
- { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142
- { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220
- { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92
- { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92
- { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675
- { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138
- { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138
- { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184
- { skbaddr: ffff880064504400 } hitcount: 4 len: 184
- { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184
- { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230
- { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196
- { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276
- { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276
-
- Totals:
- Hits: 81
- Entries: 42
- Dropped: 0
- # event histogram
- #
- # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
- #
-
- { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46
- { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76
- { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468
- { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46
- { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52
- { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168
- { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260
- { skbaddr: ffff880064505000 } hitcount: 1 len: 46
- { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32
- { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46
- { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44
- { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168
- { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40
- { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40
- { skbaddr: ffff880064505f00 } hitcount: 1 len: 174
- { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160
- { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76
- { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32
- { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988
- { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46
- { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44
- { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676
- { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107
- { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92
- { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142
- { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220
- { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92
- { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92
- { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675
- { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138
- { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138
- { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184
- { skbaddr: ffff880064504400 } hitcount: 4 len: 184
- { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184
- { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230
- { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196
- { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276
- { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276
-
- Totals:
- Hits: 81
- Entries: 42
- Dropped: 0
-
- And here's an example that shows how to combine histogram data from
- any two events even if they don't share any 'compatible' fields
- other than 'hitcount' and 'stacktrace'. These commands create a
- couple of triggers named 'bar' using those fields:
-
- # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
- # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
- /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
- And displaying the output of either shows some interesting if
- somewhat confusing output:
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
- # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
-
- # event histogram
- #
- # trigger info: hist:name=bar:keys=stacktrace:vals=hitcount:sort=hitcount:size=2048 [active]
- #
-
- { stacktrace:
- _do_fork+0x18e/0x330
- kernel_thread+0x29/0x30
- kthreadd+0x154/0x1b0
- ret_from_fork+0x3f/0x70
- } hitcount: 1
- { stacktrace:
- netif_rx_internal+0xb2/0xd0
- netif_rx_ni+0x20/0x70
- dev_loopback_xmit+0xaa/0xd0
- ip_mc_output+0x126/0x240
- ip_local_out_sk+0x31/0x40
- igmp_send_report+0x1e9/0x230
- igmp_timer_expire+0xe9/0x120
- call_timer_fn+0x39/0xf0
- run_timer_softirq+0x1e1/0x290
- __do_softirq+0xfd/0x290
- irq_exit+0x98/0xb0
- smp_apic_timer_interrupt+0x4a/0x60
- apic_timer_interrupt+0x6d/0x80
- cpuidle_enter+0x17/0x20
- call_cpuidle+0x3b/0x60
- cpu_startup_entry+0x22d/0x310
- } hitcount: 1
- { stacktrace:
- netif_rx_internal+0xb2/0xd0
- netif_rx_ni+0x20/0x70
- dev_loopback_xmit+0xaa/0xd0
- ip_mc_output+0x17f/0x240
- ip_local_out_sk+0x31/0x40
- ip_send_skb+0x1a/0x50
- udp_send_skb+0x13e/0x270
- udp_sendmsg+0x2bf/0x980
- inet_sendmsg+0x67/0xa0
- sock_sendmsg+0x38/0x50
- SYSC_sendto+0xef/0x170
- SyS_sendto+0xe/0x10
- entry_SYSCALL_64_fastpath+0x12/0x6a
- } hitcount: 2
- { stacktrace:
- netif_rx_internal+0xb2/0xd0
- netif_rx+0x1c/0x60
- loopback_xmit+0x6c/0xb0
- dev_hard_start_xmit+0x219/0x3a0
- __dev_queue_xmit+0x415/0x4f0
- dev_queue_xmit_sk+0x13/0x20
- ip_finish_output2+0x237/0x340
- ip_finish_output+0x113/0x1d0
- ip_output+0x66/0xc0
- ip_local_out_sk+0x31/0x40
- ip_send_skb+0x1a/0x50
- udp_send_skb+0x16d/0x270
- udp_sendmsg+0x2bf/0x980
- inet_sendmsg+0x67/0xa0
- sock_sendmsg+0x38/0x50
- ___sys_sendmsg+0x14e/0x270
- } hitcount: 76
- { stacktrace:
- netif_rx_internal+0xb2/0xd0
- netif_rx+0x1c/0x60
- loopback_xmit+0x6c/0xb0
- dev_hard_start_xmit+0x219/0x3a0
- __dev_queue_xmit+0x415/0x4f0
- dev_queue_xmit_sk+0x13/0x20
- ip_finish_output2+0x237/0x340
- ip_finish_output+0x113/0x1d0
- ip_output+0x66/0xc0
- ip_local_out_sk+0x31/0x40
- ip_send_skb+0x1a/0x50
- udp_send_skb+0x16d/0x270
- udp_sendmsg+0x2bf/0x980
- inet_sendmsg+0x67/0xa0
- sock_sendmsg+0x38/0x50
- ___sys_sendmsg+0x269/0x270
- } hitcount: 77
- { stacktrace:
- netif_rx_internal+0xb2/0xd0
- netif_rx+0x1c/0x60
- loopback_xmit+0x6c/0xb0
- dev_hard_start_xmit+0x219/0x3a0
- __dev_queue_xmit+0x415/0x4f0
- dev_queue_xmit_sk+0x13/0x20
- ip_finish_output2+0x237/0x340
- ip_finish_output+0x113/0x1d0
- ip_output+0x66/0xc0
- ip_local_out_sk+0x31/0x40
- ip_send_skb+0x1a/0x50
- udp_send_skb+0x16d/0x270
- udp_sendmsg+0x2bf/0x980
- inet_sendmsg+0x67/0xa0
- sock_sendmsg+0x38/0x50
- SYSC_sendto+0xef/0x170
- } hitcount: 88
- { stacktrace:
- _do_fork+0x18e/0x330
- SyS_clone+0x19/0x20
- entry_SYSCALL_64_fastpath+0x12/0x6a
- } hitcount: 244
-
- Totals:
- Hits: 489
- Entries: 7
- Dropped: 0
-
-2.2 Inter-event hist triggers
------------------------------
-
-Inter-event hist triggers are hist triggers that combine values from
-one or more other events and create a histogram using that data. Data
-from an inter-event histogram can in turn become the source for
-further combined histograms, thus providing a chain of related
-histograms, which is important for some applications.
-
-The most important example of an inter-event quantity that can be used
-in this manner is latency, which is simply a difference in timestamps
-between two events. Although latency is the most important
-inter-event quantity, note that because the support is completely
-general across the trace event subsystem, any event field can be used
-in an inter-event quantity.
-
-An example of a histogram that combines data from other histograms
-into a useful chain would be a 'wakeupswitch latency' histogram that
-combines a 'wakeup latency' histogram and a 'switch latency'
-histogram.
-
-Normally, a hist trigger specification consists of a (possibly
-compound) key along with one or more numeric values, which are
-continually updated sums associated with that key. A histogram
-specification in this case consists of individual key and value
-specifications that refer to trace event fields associated with a
-single event type.
-
-The inter-event hist trigger extension allows fields from multiple
-events to be referenced and combined into a multi-event histogram
-specification. In support of this overall goal, a few enabling
-features have been added to the hist trigger support:
-
- - In order to compute an inter-event quantity, a value from one
- event needs to saved and then referenced from another event. This
- requires the introduction of support for histogram 'variables'.
-
- - The computation of inter-event quantities and their combination
- require some minimal amount of support for applying simple
- expressions to variables (+ and -).
-
- - A histogram consisting of inter-event quantities isn't logically a
- histogram on either event (so having the 'hist' file for either
- event host the histogram output doesn't really make sense). To
- address the idea that the histogram is associated with a
- combination of events, support is added allowing the creation of
- 'synthetic' events that are events derived from other events.
- These synthetic events are full-fledged events just like any other
- and can be used as such, as for instance to create the
- 'combination' histograms mentioned previously.
-
- - A set of 'actions' can be associated with histogram entries -
- these can be used to generate the previously mentioned synthetic
- events, but can also be used for other purposes, such as for
- example saving context when a 'max' latency has been hit.
-
- - Trace events don't have a 'timestamp' associated with them, but
- there is an implicit timestamp saved along with an event in the
- underlying ftrace ring buffer. This timestamp is now exposed as a
- a synthetic field named 'common_timestamp' which can be used in
- histograms as if it were any other event field; it isn't an actual
- field in the trace format but rather is a synthesized value that
- nonetheless can be used as if it were an actual field. By default
- it is in units of nanoseconds; appending '.usecs' to a
- common_timestamp field changes the units to microseconds.
-
-A note on inter-event timestamps: If common_timestamp is used in a
-histogram, the trace buffer is automatically switched over to using
-absolute timestamps and the "global" trace clock, in order to avoid
-bogus timestamp differences with other clocks that aren't coherent
-across CPUs. This can be overridden by specifying one of the other
-trace clocks instead, using the "clock=XXX" hist trigger attribute,
-where XXX is any of the clocks listed in the tracing/trace_clock
-pseudo-file.
-
-These features are described in more detail in the following sections.
-
-2.2.1 Histogram Variables
--------------------------
-
-Variables are simply named locations used for saving and retrieving
-values between matching events. A 'matching' event is defined as an
-event that has a matching key - if a variable is saved for a histogram
-entry corresponding to that key, any subsequent event with a matching
-key can access that variable.
-
-A variable's value is normally available to any subsequent event until
-it is set to something else by a subsequent event. The one exception
-to that rule is that any variable used in an expression is essentially
-'read-once' - once it's used by an expression in a subsequent event,
-it's reset to its 'unset' state, which means it can't be used again
-unless it's set again. This ensures not only that an event doesn't
-use an uninitialized variable in a calculation, but that that variable
-is used only once and not for any unrelated subsequent match.
-
-The basic syntax for saving a variable is to simply prefix a unique
-variable name not corresponding to any keyword along with an '=' sign
-to any event field.
-
-Either keys or values can be saved and retrieved in this way. This
-creates a variable named 'ts0' for a histogram entry with the key
-'next_pid':
-
- # echo 'hist:keys=next_pid:vals=$ts0:ts0=common_timestamp ... >> \
- event/trigger
-
-The ts0 variable can be accessed by any subsequent event having the
-same pid as 'next_pid'.
-
-Variable references are formed by prepending the variable name with
-the '$' sign. Thus for example, the ts0 variable above would be
-referenced as '$ts0' in expressions.
-
-Because 'vals=' is used, the common_timestamp variable value above
-will also be summed as a normal histogram value would (though for a
-timestamp it makes little sense).
-
-The below shows that a key value can also be saved in the same way:
-
- # echo 'hist:timer_pid=common_pid:key=timer_pid ...' >> event/trigger
-
-If a variable isn't a key variable or prefixed with 'vals=', the
-associated event field will be saved in a variable but won't be summed
-as a value:
-
- # echo 'hist:keys=next_pid:ts1=common_timestamp ...' >> event/trigger
-
-Multiple variables can be assigned at the same time. The below would
-result in both ts0 and b being created as variables, with both
-common_timestamp and field1 additionally being summed as values:
-
- # echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ...' >> \
- event/trigger
-
-Note that variable assignments can appear either preceding or
-following their use. The command below behaves identically to the
-command above:
-
- # echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ...' >> \
- event/trigger
-
-Any number of variables not bound to a 'vals=' prefix can also be
-assigned by simply separating them with colons. Below is the same
-thing but without the values being summed in the histogram:
-
- # echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ...' >> event/trigger
-
-Variables set as above can be referenced and used in expressions on
-another event.
-
-For example, here's how a latency can be calculated:
-
- # echo 'hist:keys=pid,prio:ts0=common_timestamp ...' >> event1/trigger
- # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ...' >> event2/trigger
-
-In the first line above, the event's timetamp is saved into the
-variable ts0. In the next line, ts0 is subtracted from the second
-event's timestamp to produce the latency, which is then assigned into
-yet another variable, 'wakeup_lat'. The hist trigger below in turn
-makes use of the wakeup_lat variable to compute a combined latency
-using the same key and variable from yet another event:
-
- # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ...' >> event3/trigger
-
-2.2.2 Synthetic Events
-----------------------
-
-Synthetic events are user-defined events generated from hist trigger
-variables or fields associated with one or more other events. Their
-purpose is to provide a mechanism for displaying data spanning
-multiple events consistent with the existing and already familiar
-usage for normal events.
-
-To define a synthetic event, the user writes a simple specification
-consisting of the name of the new event along with one or more
-variables and their types, which can be any valid field type,
-separated by semicolons, to the tracing/synthetic_events file.
-
-For instance, the following creates a new event named 'wakeup_latency'
-with 3 fields: lat, pid, and prio. Each of those fields is simply a
-variable reference to a variable on another event:
-
- # echo 'wakeup_latency \
- u64 lat; \
- pid_t pid; \
- int prio' >> \
- /sys/kernel/debug/tracing/synthetic_events
-
-Reading the tracing/synthetic_events file lists all the currently
-defined synthetic events, in this case the event defined above:
-
- # cat /sys/kernel/debug/tracing/synthetic_events
- wakeup_latency u64 lat; pid_t pid; int prio
-
-An existing synthetic event definition can be removed by prepending
-the command that defined it with a '!':
-
- # echo '!wakeup_latency u64 lat pid_t pid int prio' >> \
- /sys/kernel/debug/tracing/synthetic_events
-
-At this point, there isn't yet an actual 'wakeup_latency' event
-instantiated in the event subsytem - for this to happen, a 'hist
-trigger action' needs to be instantiated and bound to actual fields
-and variables defined on other events (see Section 2.2.3 below on
-how that is done using hist trigger 'onmatch' action). Once that is
-done, the 'wakeup_latency' synthetic event instance is created.
-
-A histogram can now be defined for the new synthetic event:
-
- # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \
- /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
-
-The new event is created under the tracing/events/synthetic/ directory
-and looks and behaves just like any other event:
-
- # ls /sys/kernel/debug/tracing/events/synthetic/wakeup_latency
- enable filter format hist id trigger
-
-Like any other event, once a histogram is enabled for the event, the
-output can be displayed by reading the event's 'hist' file.
-
-2.2.3 Hist trigger 'actions'
-----------------------------
-
-A hist trigger 'action' is a function that's executed whenever a
-histogram entry is added or updated.
-
-The default 'action' if no special function is explicity specified is
-as it always has been, to simply update the set of values associated
-with an entry. Some applications, however, may want to perform
-additional actions at that point, such as generate another event, or
-compare and save a maximum.
-
-The following additional actions are available. To specify an action
-for a given event, simply specify the action between colons in the
-hist trigger specification.
-
- - onmatch(matching.event).<synthetic_event_name>(param list)
-
- The 'onmatch(matching.event).<synthetic_event_name>(params)' hist
- trigger action is invoked whenever an event matches and the
- histogram entry would be added or updated. It causes the named
- synthetic event to be generated with the values given in the
- 'param list'. The result is the generation of a synthetic event
- that consists of the values contained in those variables at the
- time the invoking event was hit.
-
- The 'param list' consists of one or more parameters which may be
- either variables or fields defined on either the 'matching.event'
- or the target event. The variables or fields specified in the
- param list may be either fully-qualified or unqualified. If a
- variable is specified as unqualified, it must be unique between
- the two events. A field name used as a param can be unqualified
- if it refers to the target event, but must be fully qualified if
- it refers to the matching event. A fully-qualified name is of the
- form 'system.event_name.$var_name' or 'system.event_name.field'.
-
- The 'matching.event' specification is simply the fully qualified
- event name of the event that matches the target event for the
- onmatch() functionality, in the form 'system.event_name'.
-
- Finally, the number and type of variables/fields in the 'param
- list' must match the number and types of the fields in the
- synthetic event being generated.
-
- As an example the below defines a simple synthetic event and uses
- a variable defined on the sched_wakeup_new event as a parameter
- when invoking the synthetic event. Here we define the synthetic
- event:
-
- # echo 'wakeup_new_test pid_t pid' >> \
- /sys/kernel/debug/tracing/synthetic_events
-
- # cat /sys/kernel/debug/tracing/synthetic_events
- wakeup_new_test pid_t pid
-
- The following hist trigger both defines the missing testpid
- variable and specifies an onmatch() action that generates a
- wakeup_new_test synthetic event whenever a sched_wakeup_new event
- occurs, which because of the 'if comm == "cyclictest"' filter only
- happens when the executable is cyclictest:
-
- # echo 'hist:keys=$testpid:testpid=pid:onmatch(sched.sched_wakeup_new).\
- wakeup_new_test($testpid) if comm=="cyclictest"' >> \
- /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger
-
- Creating and displaying a histogram based on those events is now
- just a matter of using the fields and new synthetic event in the
- tracing/events/synthetic directory, as usual:
-
- # echo 'hist:keys=pid:sort=pid' >> \
- /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/trigger
-
- Running 'cyclictest' should cause wakeup_new events to generate
- wakeup_new_test synthetic events which should result in histogram
- output in the wakeup_new_test event's hist file:
-
- # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/hist
-
- A more typical usage would be to use two events to calculate a
- latency. The following example uses a set of hist triggers to
- produce a 'wakeup_latency' histogram:
-
- First, we define a 'wakeup_latency' synthetic event:
-
- # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \
- /sys/kernel/debug/tracing/synthetic_events
-
- Next, we specify that whenever we see a sched_waking event for a
- cyclictest thread, save the timestamp in a 'ts0' variable:
-
- # echo 'hist:keys=$saved_pid:saved_pid=pid:ts0=common_timestamp.usecs \
- if comm=="cyclictest"' >> \
- /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
-
- Then, when the corresponding thread is actually scheduled onto the
- CPU by a sched_switch event, calculate the latency and use that
- along with another variable and an event field to generate a
- wakeup_latency synthetic event:
-
- # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0:\
- onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,\
- $saved_pid,next_prio) if next_comm=="cyclictest"' >> \
- /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
-
- We also need to create a histogram on the wakeup_latency synthetic
- event in order to aggregate the generated synthetic event data:
-
- # echo 'hist:keys=pid,prio,lat:sort=pid,lat' >> \
- /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
-
- Finally, once we've run cyclictest to actually generate some
- events, we can see the output by looking at the wakeup_latency
- synthetic event's hist file:
-
- # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist
-
- - onmax(var).save(field,.. .)
-
- The 'onmax(var).save(field,...)' hist trigger action is invoked
- whenever the value of 'var' associated with a histogram entry
- exceeds the current maximum contained in that variable.
-
- The end result is that the trace event fields specified as the
- onmax.save() params will be saved if 'var' exceeds the current
- maximum for that hist trigger entry. This allows context from the
- event that exhibited the new maximum to be saved for later
- reference. When the histogram is displayed, additional fields
- displaying the saved values will be printed.
-
- As an example the below defines a couple of hist triggers, one for
- sched_waking and another for sched_switch, keyed on pid. Whenever
- a sched_waking occurs, the timestamp is saved in the entry
- corresponding to the current pid, and when the scheduler switches
- back to that pid, the timestamp difference is calculated. If the
- resulting latency, stored in wakeup_lat, exceeds the current
- maximum latency, the values specified in the save() fields are
- recorded:
-
- # echo 'hist:keys=pid:ts0=common_timestamp.usecs \
- if comm=="cyclictest"' >> \
- /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
-
- # echo 'hist:keys=next_pid:\
- wakeup_lat=common_timestamp.usecs-$ts0:\
- onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) \
- if next_comm=="cyclictest"' >> \
- /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
-
- When the histogram is displayed, the max value and the saved
- values corresponding to the max are displayed following the rest
- of the fields:
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist
- { next_pid: 2255 } hitcount: 239
- common_timestamp-ts0: 0
- max: 27
- next_comm: cyclictest
- prev_pid: 0 prev_prio: 120 prev_comm: swapper/1
-
- { next_pid: 2256 } hitcount: 2355
- common_timestamp-ts0: 0
- max: 49 next_comm: cyclictest
- prev_pid: 0 prev_prio: 120 prev_comm: swapper/0
-
- Totals:
- Hits: 12970
- Entries: 2
- Dropped: 0
-
-3. User space creating a trigger
---------------------------------
-
-Writing into /sys/kernel/tracing/trace_marker writes into the ftrace
-ring buffer. This can also act like an event, by writing into the trigger
-file located in /sys/kernel/tracing/events/ftrace/print/
-
-Modifying cyclictest to write into the trace_marker file before it sleeps
-and after it wakes up, something like this:
-
-static void traceputs(char *str)
-{
- /* tracemark_fd is the trace_marker file descriptor */
- if (tracemark_fd < 0)
- return;
- /* write the tracemark message */
- write(tracemark_fd, str, strlen(str));
-}
-
-And later add something like:
-
- traceputs("start");
- clock_nanosleep(...);
- traceputs("end");
-
-We can make a histogram from this:
-
- # cd /sys/kernel/tracing
- # echo 'latency u64 lat' > synthetic_events
- # echo 'hist:keys=common_pid:ts0=common_timestamp.usecs if buf == "start"' > events/ftrace/print/trigger
- # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(ftrace.print).latency($lat) if buf == "end"' >> events/ftrace/print/trigger
- # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger
-
-The above created a synthetic event called "latency" and two histograms
-against the trace_marker, one gets triggered when "start" is written into the
-trace_marker file and the other when "end" is written. If the pids match, then
-it will call the "latency" synthetic event with the calculated latency as its
-parameter. Finally, a histogram is added to the latency synthetic event to
-record the calculated latency along with the pid.
-
-Now running cyclictest with:
-
- # ./cyclictest -p80 -d0 -i250 -n -a -t --tracemark -b 1000
-
- -p80 : run threads at priority 80
- -d0 : have all threads run at the same interval
- -i250 : start the interval at 250 microseconds (all threads will do this)
- -n : sleep with nanosleep
- -a : affine all threads to a separate CPU
- -t : one thread per available CPU
- --tracemark : enable trace mark writing
- -b 1000 : stop if any latency is greater than 1000 microseconds
-
-Note, the -b 1000 is used just to make --tracemark available.
-
-Then we can see the histogram created by this with:
-
- # cat events/synthetic/latency/hist
-# event histogram
-#
-# trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active]
-#
-
-{ lat: 107, common_pid: 2039 } hitcount: 1
-{ lat: 122, common_pid: 2041 } hitcount: 1
-{ lat: 166, common_pid: 2039 } hitcount: 1
-{ lat: 174, common_pid: 2039 } hitcount: 1
-{ lat: 194, common_pid: 2041 } hitcount: 1
-{ lat: 196, common_pid: 2036 } hitcount: 1
-{ lat: 197, common_pid: 2038 } hitcount: 1
-{ lat: 198, common_pid: 2039 } hitcount: 1
-{ lat: 199, common_pid: 2039 } hitcount: 1
-{ lat: 200, common_pid: 2041 } hitcount: 1
-{ lat: 201, common_pid: 2039 } hitcount: 2
-{ lat: 202, common_pid: 2038 } hitcount: 1
-{ lat: 202, common_pid: 2043 } hitcount: 1
-{ lat: 203, common_pid: 2039 } hitcount: 1
-{ lat: 203, common_pid: 2036 } hitcount: 1
-{ lat: 203, common_pid: 2041 } hitcount: 1
-{ lat: 206, common_pid: 2038 } hitcount: 2
-{ lat: 207, common_pid: 2039 } hitcount: 1
-{ lat: 207, common_pid: 2036 } hitcount: 1
-{ lat: 208, common_pid: 2040 } hitcount: 1
-{ lat: 209, common_pid: 2043 } hitcount: 1
-{ lat: 210, common_pid: 2039 } hitcount: 1
-{ lat: 211, common_pid: 2039 } hitcount: 4
-{ lat: 212, common_pid: 2043 } hitcount: 1
-{ lat: 212, common_pid: 2039 } hitcount: 2
-{ lat: 213, common_pid: 2039 } hitcount: 1
-{ lat: 214, common_pid: 2038 } hitcount: 1
-{ lat: 214, common_pid: 2039 } hitcount: 2
-{ lat: 214, common_pid: 2042 } hitcount: 1
-{ lat: 215, common_pid: 2039 } hitcount: 1
-{ lat: 217, common_pid: 2036 } hitcount: 1
-{ lat: 217, common_pid: 2040 } hitcount: 1
-{ lat: 217, common_pid: 2039 } hitcount: 1
-{ lat: 218, common_pid: 2039 } hitcount: 6
-{ lat: 219, common_pid: 2039 } hitcount: 9
-{ lat: 220, common_pid: 2039 } hitcount: 11
-{ lat: 221, common_pid: 2039 } hitcount: 5
-{ lat: 221, common_pid: 2042 } hitcount: 1
-{ lat: 222, common_pid: 2039 } hitcount: 7
-{ lat: 223, common_pid: 2036 } hitcount: 1
-{ lat: 223, common_pid: 2039 } hitcount: 3
-{ lat: 224, common_pid: 2039 } hitcount: 4
-{ lat: 224, common_pid: 2037 } hitcount: 1
-{ lat: 224, common_pid: 2036 } hitcount: 2
-{ lat: 225, common_pid: 2039 } hitcount: 5
-{ lat: 225, common_pid: 2042 } hitcount: 1
-{ lat: 226, common_pid: 2039 } hitcount: 7
-{ lat: 226, common_pid: 2036 } hitcount: 4
-{ lat: 227, common_pid: 2039 } hitcount: 6
-{ lat: 227, common_pid: 2036 } hitcount: 12
-{ lat: 227, common_pid: 2043 } hitcount: 1
-{ lat: 228, common_pid: 2039 } hitcount: 7
-{ lat: 228, common_pid: 2036 } hitcount: 14
-{ lat: 229, common_pid: 2039 } hitcount: 9
-{ lat: 229, common_pid: 2036 } hitcount: 8
-{ lat: 229, common_pid: 2038 } hitcount: 1
-{ lat: 230, common_pid: 2039 } hitcount: 11
-{ lat: 230, common_pid: 2036 } hitcount: 6
-{ lat: 230, common_pid: 2043 } hitcount: 1
-{ lat: 230, common_pid: 2042 } hitcount: 2
-{ lat: 231, common_pid: 2041 } hitcount: 1
-{ lat: 231, common_pid: 2036 } hitcount: 6
-{ lat: 231, common_pid: 2043 } hitcount: 1
-{ lat: 231, common_pid: 2039 } hitcount: 8
-{ lat: 232, common_pid: 2037 } hitcount: 1
-{ lat: 232, common_pid: 2039 } hitcount: 6
-{ lat: 232, common_pid: 2040 } hitcount: 2
-{ lat: 232, common_pid: 2036 } hitcount: 5
-{ lat: 232, common_pid: 2043 } hitcount: 1
-{ lat: 233, common_pid: 2036 } hitcount: 5
-{ lat: 233, common_pid: 2039 } hitcount: 11
-{ lat: 234, common_pid: 2039 } hitcount: 4
-{ lat: 234, common_pid: 2038 } hitcount: 2
-{ lat: 234, common_pid: 2043 } hitcount: 2
-{ lat: 234, common_pid: 2036 } hitcount: 11
-{ lat: 234, common_pid: 2040 } hitcount: 1
-{ lat: 235, common_pid: 2037 } hitcount: 2
-{ lat: 235, common_pid: 2036 } hitcount: 8
-{ lat: 235, common_pid: 2043 } hitcount: 2
-{ lat: 235, common_pid: 2039 } hitcount: 5
-{ lat: 235, common_pid: 2042 } hitcount: 2
-{ lat: 235, common_pid: 2040 } hitcount: 4
-{ lat: 235, common_pid: 2041 } hitcount: 1
-{ lat: 236, common_pid: 2036 } hitcount: 7
-{ lat: 236, common_pid: 2037 } hitcount: 1
-{ lat: 236, common_pid: 2041 } hitcount: 5
-{ lat: 236, common_pid: 2039 } hitcount: 3
-{ lat: 236, common_pid: 2043 } hitcount: 9
-{ lat: 236, common_pid: 2040 } hitcount: 7
-{ lat: 237, common_pid: 2037 } hitcount: 1
-{ lat: 237, common_pid: 2040 } hitcount: 1
-{ lat: 237, common_pid: 2036 } hitcount: 9
-{ lat: 237, common_pid: 2039 } hitcount: 3
-{ lat: 237, common_pid: 2043 } hitcount: 8
-{ lat: 237, common_pid: 2042 } hitcount: 2
-{ lat: 237, common_pid: 2041 } hitcount: 2
-{ lat: 238, common_pid: 2043 } hitcount: 10
-{ lat: 238, common_pid: 2040 } hitcount: 1
-{ lat: 238, common_pid: 2037 } hitcount: 9
-{ lat: 238, common_pid: 2038 } hitcount: 1
-{ lat: 238, common_pid: 2039 } hitcount: 1
-{ lat: 238, common_pid: 2042 } hitcount: 3
-{ lat: 238, common_pid: 2036 } hitcount: 7
-{ lat: 239, common_pid: 2041 } hitcount: 1
-{ lat: 239, common_pid: 2043 } hitcount: 11
-{ lat: 239, common_pid: 2037 } hitcount: 11
-{ lat: 239, common_pid: 2038 } hitcount: 6
-{ lat: 239, common_pid: 2036 } hitcount: 7
-{ lat: 239, common_pid: 2040 } hitcount: 1
-{ lat: 239, common_pid: 2042 } hitcount: 9
-{ lat: 240, common_pid: 2037 } hitcount: 29
-{ lat: 240, common_pid: 2043 } hitcount: 15
-{ lat: 240, common_pid: 2040 } hitcount: 44
-{ lat: 240, common_pid: 2039 } hitcount: 1
-{ lat: 240, common_pid: 2041 } hitcount: 2
-{ lat: 240, common_pid: 2038 } hitcount: 1
-{ lat: 240, common_pid: 2036 } hitcount: 10
-{ lat: 240, common_pid: 2042 } hitcount: 13
-{ lat: 241, common_pid: 2036 } hitcount: 21
-{ lat: 241, common_pid: 2041 } hitcount: 36
-{ lat: 241, common_pid: 2037 } hitcount: 34
-{ lat: 241, common_pid: 2042 } hitcount: 14
-{ lat: 241, common_pid: 2040 } hitcount: 94
-{ lat: 241, common_pid: 2039 } hitcount: 12
-{ lat: 241, common_pid: 2038 } hitcount: 2
-{ lat: 241, common_pid: 2043 } hitcount: 28
-{ lat: 242, common_pid: 2040 } hitcount: 109
-{ lat: 242, common_pid: 2041 } hitcount: 506
-{ lat: 242, common_pid: 2039 } hitcount: 155
-{ lat: 242, common_pid: 2042 } hitcount: 21
-{ lat: 242, common_pid: 2037 } hitcount: 52
-{ lat: 242, common_pid: 2043 } hitcount: 21
-{ lat: 242, common_pid: 2036 } hitcount: 16
-{ lat: 242, common_pid: 2038 } hitcount: 156
-{ lat: 243, common_pid: 2037 } hitcount: 46
-{ lat: 243, common_pid: 2039 } hitcount: 40
-{ lat: 243, common_pid: 2042 } hitcount: 119
-{ lat: 243, common_pid: 2041 } hitcount: 611
-{ lat: 243, common_pid: 2036 } hitcount: 69
-{ lat: 243, common_pid: 2038 } hitcount: 784
-{ lat: 243, common_pid: 2040 } hitcount: 323
-{ lat: 243, common_pid: 2043 } hitcount: 14
-{ lat: 244, common_pid: 2043 } hitcount: 35
-{ lat: 244, common_pid: 2042 } hitcount: 305
-{ lat: 244, common_pid: 2039 } hitcount: 8
-{ lat: 244, common_pid: 2040 } hitcount: 4515
-{ lat: 244, common_pid: 2038 } hitcount: 371
-{ lat: 244, common_pid: 2037 } hitcount: 31
-{ lat: 244, common_pid: 2036 } hitcount: 114
-{ lat: 244, common_pid: 2041 } hitcount: 3396
-{ lat: 245, common_pid: 2036 } hitcount: 700
-{ lat: 245, common_pid: 2041 } hitcount: 2772
-{ lat: 245, common_pid: 2037 } hitcount: 268
-{ lat: 245, common_pid: 2039 } hitcount: 472
-{ lat: 245, common_pid: 2038 } hitcount: 2758
-{ lat: 245, common_pid: 2042 } hitcount: 3833
-{ lat: 245, common_pid: 2040 } hitcount: 3105
-{ lat: 245, common_pid: 2043 } hitcount: 645
-{ lat: 246, common_pid: 2038 } hitcount: 3451
-{ lat: 246, common_pid: 2041 } hitcount: 142
-{ lat: 246, common_pid: 2037 } hitcount: 5101
-{ lat: 246, common_pid: 2040 } hitcount: 68
-{ lat: 246, common_pid: 2043 } hitcount: 5099
-{ lat: 246, common_pid: 2039 } hitcount: 5608
-{ lat: 246, common_pid: 2042 } hitcount: 3723
-{ lat: 246, common_pid: 2036 } hitcount: 4738
-{ lat: 247, common_pid: 2042 } hitcount: 312
-{ lat: 247, common_pid: 2043 } hitcount: 2385
-{ lat: 247, common_pid: 2041 } hitcount: 452
-{ lat: 247, common_pid: 2038 } hitcount: 792
-{ lat: 247, common_pid: 2040 } hitcount: 78
-{ lat: 247, common_pid: 2036 } hitcount: 2375
-{ lat: 247, common_pid: 2039 } hitcount: 1834
-{ lat: 247, common_pid: 2037 } hitcount: 2655
-{ lat: 248, common_pid: 2037 } hitcount: 36
-{ lat: 248, common_pid: 2042 } hitcount: 11
-{ lat: 248, common_pid: 2038 } hitcount: 122
-{ lat: 248, common_pid: 2036 } hitcount: 135
-{ lat: 248, common_pid: 2039 } hitcount: 26
-{ lat: 248, common_pid: 2041 } hitcount: 503
-{ lat: 248, common_pid: 2043 } hitcount: 66
-{ lat: 248, common_pid: 2040 } hitcount: 46
-{ lat: 249, common_pid: 2037 } hitcount: 29
-{ lat: 249, common_pid: 2038 } hitcount: 1
-{ lat: 249, common_pid: 2043 } hitcount: 29
-{ lat: 249, common_pid: 2039 } hitcount: 8
-{ lat: 249, common_pid: 2042 } hitcount: 56
-{ lat: 249, common_pid: 2040 } hitcount: 27
-{ lat: 249, common_pid: 2041 } hitcount: 11
-{ lat: 249, common_pid: 2036 } hitcount: 27
-{ lat: 250, common_pid: 2038 } hitcount: 1
-{ lat: 250, common_pid: 2036 } hitcount: 30
-{ lat: 250, common_pid: 2040 } hitcount: 19
-{ lat: 250, common_pid: 2043 } hitcount: 22
-{ lat: 250, common_pid: 2042 } hitcount: 20
-{ lat: 250, common_pid: 2041 } hitcount: 1
-{ lat: 250, common_pid: 2039 } hitcount: 6
-{ lat: 250, common_pid: 2037 } hitcount: 48
-{ lat: 251, common_pid: 2037 } hitcount: 43
-{ lat: 251, common_pid: 2039 } hitcount: 1
-{ lat: 251, common_pid: 2036 } hitcount: 12
-{ lat: 251, common_pid: 2042 } hitcount: 2
-{ lat: 251, common_pid: 2041 } hitcount: 1
-{ lat: 251, common_pid: 2043 } hitcount: 15
-{ lat: 251, common_pid: 2040 } hitcount: 3
-{ lat: 252, common_pid: 2040 } hitcount: 1
-{ lat: 252, common_pid: 2036 } hitcount: 12
-{ lat: 252, common_pid: 2037 } hitcount: 21
-{ lat: 252, common_pid: 2043 } hitcount: 14
-{ lat: 253, common_pid: 2037 } hitcount: 21
-{ lat: 253, common_pid: 2039 } hitcount: 2
-{ lat: 253, common_pid: 2036 } hitcount: 9
-{ lat: 253, common_pid: 2043 } hitcount: 6
-{ lat: 253, common_pid: 2040 } hitcount: 1
-{ lat: 254, common_pid: 2036 } hitcount: 8
-{ lat: 254, common_pid: 2043 } hitcount: 3
-{ lat: 254, common_pid: 2041 } hitcount: 1
-{ lat: 254, common_pid: 2042 } hitcount: 1
-{ lat: 254, common_pid: 2039 } hitcount: 1
-{ lat: 254, common_pid: 2037 } hitcount: 12
-{ lat: 255, common_pid: 2043 } hitcount: 1
-{ lat: 255, common_pid: 2037 } hitcount: 2
-{ lat: 255, common_pid: 2036 } hitcount: 2
-{ lat: 255, common_pid: 2039 } hitcount: 8
-{ lat: 256, common_pid: 2043 } hitcount: 1
-{ lat: 256, common_pid: 2036 } hitcount: 4
-{ lat: 256, common_pid: 2039 } hitcount: 6
-{ lat: 257, common_pid: 2039 } hitcount: 5
-{ lat: 257, common_pid: 2036 } hitcount: 4
-{ lat: 258, common_pid: 2039 } hitcount: 5
-{ lat: 258, common_pid: 2036 } hitcount: 2
-{ lat: 259, common_pid: 2036 } hitcount: 7
-{ lat: 259, common_pid: 2039 } hitcount: 7
-{ lat: 260, common_pid: 2036 } hitcount: 8
-{ lat: 260, common_pid: 2039 } hitcount: 6
-{ lat: 261, common_pid: 2036 } hitcount: 5
-{ lat: 261, common_pid: 2039 } hitcount: 7
-{ lat: 262, common_pid: 2039 } hitcount: 5
-{ lat: 262, common_pid: 2036 } hitcount: 5
-{ lat: 263, common_pid: 2039 } hitcount: 7
-{ lat: 263, common_pid: 2036 } hitcount: 7
-{ lat: 264, common_pid: 2039 } hitcount: 9
-{ lat: 264, common_pid: 2036 } hitcount: 9
-{ lat: 265, common_pid: 2036 } hitcount: 5
-{ lat: 265, common_pid: 2039 } hitcount: 1
-{ lat: 266, common_pid: 2036 } hitcount: 1
-{ lat: 266, common_pid: 2039 } hitcount: 3
-{ lat: 267, common_pid: 2036 } hitcount: 1
-{ lat: 267, common_pid: 2039 } hitcount: 3
-{ lat: 268, common_pid: 2036 } hitcount: 1
-{ lat: 268, common_pid: 2039 } hitcount: 6
-{ lat: 269, common_pid: 2036 } hitcount: 1
-{ lat: 269, common_pid: 2043 } hitcount: 1
-{ lat: 269, common_pid: 2039 } hitcount: 2
-{ lat: 270, common_pid: 2040 } hitcount: 1
-{ lat: 270, common_pid: 2039 } hitcount: 6
-{ lat: 271, common_pid: 2041 } hitcount: 1
-{ lat: 271, common_pid: 2039 } hitcount: 5
-{ lat: 272, common_pid: 2039 } hitcount: 10
-{ lat: 273, common_pid: 2039 } hitcount: 8
-{ lat: 274, common_pid: 2039 } hitcount: 2
-{ lat: 275, common_pid: 2039 } hitcount: 1
-{ lat: 276, common_pid: 2039 } hitcount: 2
-{ lat: 276, common_pid: 2037 } hitcount: 1
-{ lat: 276, common_pid: 2038 } hitcount: 1
-{ lat: 277, common_pid: 2039 } hitcount: 1
-{ lat: 277, common_pid: 2042 } hitcount: 1
-{ lat: 278, common_pid: 2039 } hitcount: 1
-{ lat: 279, common_pid: 2039 } hitcount: 4
-{ lat: 279, common_pid: 2043 } hitcount: 1
-{ lat: 280, common_pid: 2039 } hitcount: 3
-{ lat: 283, common_pid: 2036 } hitcount: 2
-{ lat: 284, common_pid: 2039 } hitcount: 1
-{ lat: 284, common_pid: 2043 } hitcount: 1
-{ lat: 288, common_pid: 2039 } hitcount: 1
-{ lat: 289, common_pid: 2039 } hitcount: 1
-{ lat: 300, common_pid: 2039 } hitcount: 1
-{ lat: 384, common_pid: 2039 } hitcount: 1
-
-Totals:
- Hits: 67625
- Entries: 278
- Dropped: 0
-
-Note, the writes are around the sleep, so ideally they will all be of 250
-microseconds. If you are wondering how there are several that are under
-250 microseconds, that is because the way cyclictest works, is if one
-iteration comes in late, the next one will set the timer to wake up less that
-250. That is, if an iteration came in 50 microseconds late, the next wake up
-will be at 200 microseconds.
-
-But this could easily be done in userspace. To make this even more
-interesting, we can mix the histogram between events that happened in the
-kernel with trace_marker.
-
- # cd /sys/kernel/tracing
- # echo 'latency u64 lat' > synthetic_events
- # echo 'hist:keys=pid:ts0=common_timestamp.usecs' > events/sched/sched_waking/trigger
- # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(sched.sched_waking).latency($lat) if buf == "end"' > events/ftrace/print/trigger
- # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger
-
-The difference this time is that instead of using the trace_marker to start
-the latency, the sched_waking event is used, matching the common_pid for the
-trace_marker write with the pid that is being woken by sched_waking.
-
-After running cyclictest again with the same parameters, we now have:
-
- # cat events/synthetic/latency/hist
-# event histogram
-#
-# trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active]
-#
-
-{ lat: 7, common_pid: 2302 } hitcount: 640
-{ lat: 7, common_pid: 2299 } hitcount: 42
-{ lat: 7, common_pid: 2303 } hitcount: 18
-{ lat: 7, common_pid: 2305 } hitcount: 166
-{ lat: 7, common_pid: 2306 } hitcount: 1
-{ lat: 7, common_pid: 2301 } hitcount: 91
-{ lat: 7, common_pid: 2300 } hitcount: 17
-{ lat: 8, common_pid: 2303 } hitcount: 8296
-{ lat: 8, common_pid: 2304 } hitcount: 6864
-{ lat: 8, common_pid: 2305 } hitcount: 9464
-{ lat: 8, common_pid: 2301 } hitcount: 9213
-{ lat: 8, common_pid: 2306 } hitcount: 6246
-{ lat: 8, common_pid: 2302 } hitcount: 8797
-{ lat: 8, common_pid: 2299 } hitcount: 8771
-{ lat: 8, common_pid: 2300 } hitcount: 8119
-{ lat: 9, common_pid: 2305 } hitcount: 1519
-{ lat: 9, common_pid: 2299 } hitcount: 2346
-{ lat: 9, common_pid: 2303 } hitcount: 2841
-{ lat: 9, common_pid: 2301 } hitcount: 1846
-{ lat: 9, common_pid: 2304 } hitcount: 3861
-{ lat: 9, common_pid: 2302 } hitcount: 1210
-{ lat: 9, common_pid: 2300 } hitcount: 2762
-{ lat: 9, common_pid: 2306 } hitcount: 4247
-{ lat: 10, common_pid: 2299 } hitcount: 16
-{ lat: 10, common_pid: 2306 } hitcount: 333
-{ lat: 10, common_pid: 2303 } hitcount: 16
-{ lat: 10, common_pid: 2304 } hitcount: 168
-{ lat: 10, common_pid: 2302 } hitcount: 240
-{ lat: 10, common_pid: 2301 } hitcount: 28
-{ lat: 10, common_pid: 2300 } hitcount: 95
-{ lat: 10, common_pid: 2305 } hitcount: 18
-{ lat: 11, common_pid: 2303 } hitcount: 5
-{ lat: 11, common_pid: 2305 } hitcount: 8
-{ lat: 11, common_pid: 2306 } hitcount: 221
-{ lat: 11, common_pid: 2302 } hitcount: 76
-{ lat: 11, common_pid: 2304 } hitcount: 26
-{ lat: 11, common_pid: 2300 } hitcount: 125
-{ lat: 11, common_pid: 2299 } hitcount: 2
-{ lat: 12, common_pid: 2305 } hitcount: 3
-{ lat: 12, common_pid: 2300 } hitcount: 6
-{ lat: 12, common_pid: 2306 } hitcount: 90
-{ lat: 12, common_pid: 2302 } hitcount: 4
-{ lat: 12, common_pid: 2303 } hitcount: 1
-{ lat: 12, common_pid: 2304 } hitcount: 122
-{ lat: 13, common_pid: 2300 } hitcount: 12
-{ lat: 13, common_pid: 2301 } hitcount: 1
-{ lat: 13, common_pid: 2306 } hitcount: 32
-{ lat: 13, common_pid: 2302 } hitcount: 5
-{ lat: 13, common_pid: 2305 } hitcount: 1
-{ lat: 13, common_pid: 2303 } hitcount: 1
-{ lat: 13, common_pid: 2304 } hitcount: 61
-{ lat: 14, common_pid: 2303 } hitcount: 4
-{ lat: 14, common_pid: 2306 } hitcount: 5
-{ lat: 14, common_pid: 2305 } hitcount: 4
-{ lat: 14, common_pid: 2304 } hitcount: 62
-{ lat: 14, common_pid: 2302 } hitcount: 19
-{ lat: 14, common_pid: 2300 } hitcount: 33
-{ lat: 14, common_pid: 2299 } hitcount: 1
-{ lat: 14, common_pid: 2301 } hitcount: 4
-{ lat: 15, common_pid: 2305 } hitcount: 1
-{ lat: 15, common_pid: 2302 } hitcount: 25
-{ lat: 15, common_pid: 2300 } hitcount: 11
-{ lat: 15, common_pid: 2299 } hitcount: 5
-{ lat: 15, common_pid: 2301 } hitcount: 1
-{ lat: 15, common_pid: 2304 } hitcount: 8
-{ lat: 15, common_pid: 2303 } hitcount: 1
-{ lat: 15, common_pid: 2306 } hitcount: 6
-{ lat: 16, common_pid: 2302 } hitcount: 31
-{ lat: 16, common_pid: 2306 } hitcount: 3
-{ lat: 16, common_pid: 2300 } hitcount: 5
-{ lat: 17, common_pid: 2302 } hitcount: 6
-{ lat: 17, common_pid: 2303 } hitcount: 1
-{ lat: 18, common_pid: 2304 } hitcount: 1
-{ lat: 18, common_pid: 2302 } hitcount: 8
-{ lat: 18, common_pid: 2299 } hitcount: 1
-{ lat: 18, common_pid: 2301 } hitcount: 1
-{ lat: 19, common_pid: 2303 } hitcount: 4
-{ lat: 19, common_pid: 2304 } hitcount: 5
-{ lat: 19, common_pid: 2302 } hitcount: 4
-{ lat: 19, common_pid: 2299 } hitcount: 3
-{ lat: 19, common_pid: 2306 } hitcount: 1
-{ lat: 19, common_pid: 2300 } hitcount: 4
-{ lat: 19, common_pid: 2305 } hitcount: 5
-{ lat: 20, common_pid: 2299 } hitcount: 2
-{ lat: 20, common_pid: 2302 } hitcount: 3
-{ lat: 20, common_pid: 2305 } hitcount: 1
-{ lat: 20, common_pid: 2300 } hitcount: 2
-{ lat: 20, common_pid: 2301 } hitcount: 2
-{ lat: 20, common_pid: 2303 } hitcount: 3
-{ lat: 21, common_pid: 2305 } hitcount: 1
-{ lat: 21, common_pid: 2299 } hitcount: 5
-{ lat: 21, common_pid: 2303 } hitcount: 4
-{ lat: 21, common_pid: 2302 } hitcount: 7
-{ lat: 21, common_pid: 2300 } hitcount: 1
-{ lat: 21, common_pid: 2301 } hitcount: 5
-{ lat: 21, common_pid: 2304 } hitcount: 2
-{ lat: 22, common_pid: 2302 } hitcount: 5
-{ lat: 22, common_pid: 2303 } hitcount: 1
-{ lat: 22, common_pid: 2306 } hitcount: 3
-{ lat: 22, common_pid: 2301 } hitcount: 2
-{ lat: 22, common_pid: 2300 } hitcount: 1
-{ lat: 22, common_pid: 2299 } hitcount: 1
-{ lat: 22, common_pid: 2305 } hitcount: 1
-{ lat: 22, common_pid: 2304 } hitcount: 1
-{ lat: 23, common_pid: 2299 } hitcount: 1
-{ lat: 23, common_pid: 2306 } hitcount: 2
-{ lat: 23, common_pid: 2302 } hitcount: 6
-{ lat: 24, common_pid: 2302 } hitcount: 3
-{ lat: 24, common_pid: 2300 } hitcount: 1
-{ lat: 24, common_pid: 2306 } hitcount: 2
-{ lat: 24, common_pid: 2305 } hitcount: 1
-{ lat: 24, common_pid: 2299 } hitcount: 1
-{ lat: 25, common_pid: 2300 } hitcount: 1
-{ lat: 25, common_pid: 2302 } hitcount: 4
-{ lat: 26, common_pid: 2302 } hitcount: 2
-{ lat: 27, common_pid: 2305 } hitcount: 1
-{ lat: 27, common_pid: 2300 } hitcount: 1
-{ lat: 27, common_pid: 2302 } hitcount: 3
-{ lat: 28, common_pid: 2306 } hitcount: 1
-{ lat: 28, common_pid: 2302 } hitcount: 4
-{ lat: 29, common_pid: 2302 } hitcount: 1
-{ lat: 29, common_pid: 2300 } hitcount: 2
-{ lat: 29, common_pid: 2306 } hitcount: 1
-{ lat: 29, common_pid: 2304 } hitcount: 1
-{ lat: 30, common_pid: 2302 } hitcount: 4
-{ lat: 31, common_pid: 2302 } hitcount: 6
-{ lat: 32, common_pid: 2302 } hitcount: 1
-{ lat: 33, common_pid: 2299 } hitcount: 1
-{ lat: 33, common_pid: 2302 } hitcount: 3
-{ lat: 34, common_pid: 2302 } hitcount: 2
-{ lat: 35, common_pid: 2302 } hitcount: 1
-{ lat: 35, common_pid: 2304 } hitcount: 1
-{ lat: 36, common_pid: 2302 } hitcount: 4
-{ lat: 37, common_pid: 2302 } hitcount: 6
-{ lat: 38, common_pid: 2302 } hitcount: 2
-{ lat: 39, common_pid: 2302 } hitcount: 2
-{ lat: 39, common_pid: 2304 } hitcount: 1
-{ lat: 40, common_pid: 2304 } hitcount: 2
-{ lat: 40, common_pid: 2302 } hitcount: 5
-{ lat: 41, common_pid: 2304 } hitcount: 1
-{ lat: 41, common_pid: 2302 } hitcount: 8
-{ lat: 42, common_pid: 2302 } hitcount: 6
-{ lat: 42, common_pid: 2304 } hitcount: 1
-{ lat: 43, common_pid: 2302 } hitcount: 3
-{ lat: 43, common_pid: 2304 } hitcount: 4
-{ lat: 44, common_pid: 2302 } hitcount: 6
-{ lat: 45, common_pid: 2302 } hitcount: 5
-{ lat: 46, common_pid: 2302 } hitcount: 5
-{ lat: 47, common_pid: 2302 } hitcount: 7
-{ lat: 48, common_pid: 2301 } hitcount: 1
-{ lat: 48, common_pid: 2302 } hitcount: 9
-{ lat: 49, common_pid: 2302 } hitcount: 3
-{ lat: 50, common_pid: 2302 } hitcount: 1
-{ lat: 50, common_pid: 2301 } hitcount: 1
-{ lat: 51, common_pid: 2302 } hitcount: 2
-{ lat: 51, common_pid: 2301 } hitcount: 1
-{ lat: 61, common_pid: 2302 } hitcount: 1
-{ lat: 110, common_pid: 2302 } hitcount: 1
-
-Totals:
- Hits: 89565
- Entries: 158
- Dropped: 0
-
-This doesn't tell us any information about how late cyclictest may have
-woken up, but it does show us a nice histogram of how long it took from
-the time that cyclictest was woken to the time it made it into user space.
projects / mirror_ubuntu-focal-kernel.git / commitdiff