perf-sched(1)
=============

NAME
----
perf-sched - Tool to trace/measure scheduler properties (latencies)

SYNOPSIS
--------
[verse]
'perf sched' {record|latency|map|replay|script|timehist|stats}

DESCRIPTION
-----------
There are several variants of 'perf sched':

  'perf sched record <command>' to record the scheduling events
  of an arbitrary workload.

  'perf sched latency' to report the per task scheduling latencies
  and other scheduling properties of the workload.

   Example usage:
       perf sched record -- sleep 1
       perf sched latency

  -------------------------------------------------------------------------------------------------------------------------------------------
  Task                  |   Runtime ms  |  Count   | Avg delay ms    | Max delay ms    | Max delay start           | Max delay end          |
  -------------------------------------------------------------------------------------------------------------------------------------------
  perf:(2)              |      2.804 ms |       66 | avg:   0.524 ms | max:   1.069 ms | max start: 254752.314960 s | max end: 254752.316029 s
  NetworkManager:1343   |      0.372 ms |       13 | avg:   0.008 ms | max:   0.013 ms | max start: 254751.551153 s | max end: 254751.551166 s
  kworker/1:2-xfs:4649  |      0.012 ms |        1 | avg:   0.008 ms | max:   0.008 ms | max start: 254751.519807 s | max end: 254751.519815 s
  kworker/3:1-xfs:388   |      0.011 ms |        1 | avg:   0.006 ms | max:   0.006 ms | max start: 254751.519809 s | max end: 254751.519815 s
  sleep:147736          |      0.938 ms |        3 | avg:   0.006 ms | max:   0.007 ms | max start: 254751.313817 s | max end: 254751.313824 s

  It shows Runtime(time that a task spent actually running on the CPU),
  Count(number of times a delay was calculated) and delay(time that a
  task was ready to run but was kept waiting).

  Tasks with the same command name are merged and the merge count is
  given within (), However if -p option is used, pid is mentioned.

  'perf sched script' to see a detailed trace of the workload that
   was recorded (aliased to 'perf script' for now).

  'perf sched replay' to simulate the workload that was recorded
  via perf sched record. (this is done by starting up mockup threads
  that mimic the workload based on the events in the trace. These
  threads can then replay the timings (CPU runtime and sleep patterns)
  of the workload as it occurred when it was recorded - and can repeat
  it a number of times, measuring its performance.)

  'perf sched map' to print a textual context-switching outline of
  workload captured via perf sched record.  Columns stand for
  individual CPUs, and the two-letter shortcuts stand for tasks that
  are running on a CPU. A '*' denotes the CPU that had the event, and
  a dot signals an idle CPU.

  'perf sched timehist' provides an analysis of scheduling events.
    
    Example usage:
        perf sched record -- sleep 1
        perf sched timehist
    
   By default it shows the individual schedule events, including the wait
   time (time between sched-out and next sched-in events for the task), the
   task scheduling delay (time between runnable and actually running) and
   run time for the task:
    
                time    cpu  task name             wait time  sch delay   run time
                             [tid/pid]                (msec)     (msec)     (msec)
      -------------- ------  --------------------  ---------  ---------  ---------
        79371.874569 [0011]  gcc[31949]                0.014      0.000      1.148
        79371.874591 [0010]  gcc[31951]                0.000      0.000      0.024
        79371.874603 [0010]  migration/10[59]          3.350      0.004      0.011
        79371.874604 [0011]  <idle>                    1.148      0.000      0.035
        79371.874723 [0005]  <idle>                    0.016      0.000      1.383
        79371.874746 [0005]  gcc[31949]                0.153      0.078      0.022
    ...
    
   Times are in msec.usec.

   'perf sched stats {record | report | diff} <command>' to capture, report the diff
   in schedstat counters and show the difference between perf sched stats report
   respectively. schedstat counters which are present in the linux kernel and are
   exposed through the file ``/proc/schedstat``. These counters are enabled or disabled
   via the sysctl governed by the file ``/proc/sys/kernel/sched_schedstats``. These
   counters accounts for many scheduler events such as ``schedule()`` calls, load-balancing
   events, ``try_to_wakeup()`` call among others. This is useful in understanding the
   scheduler behavior for the workload.

   Note: The tool will not give correct results if there is topological reordering or
         online/offline of cpus in between capturing snapshots of `/proc/schedstat`.

    Example usage:
        perf sched stats record -- sleep 1
        perf sched stats report
        perf sched stats diff

   A detailed description of the schedstats can be found in the Kernel Documentation:
   https://www.kernel.org/doc/html/latest/scheduler/sched-stats.html

   The result can be interpreted as follows:

   The `perf sched stats report` starts with description of the columns present in
   the report. These column names are given before cpu and domain stats to improve
   the readability of the report.

   ----------------------------------------------------------------------------------------------------
   DESC                    -> Description of the field
   COUNT                   -> Value of the field
   PCT_CHANGE              -> Percent change with corresponding base value
   AVG_JIFFIES             -> Avg time in jiffies between two consecutive occurrence of event
   ----------------------------------------------------------------------------------------------------

   Next is the total profiling time in terms of jiffies:

   ----------------------------------------------------------------------------------------------------
   Time elapsed (in jiffies)                                   :        2323
   ----------------------------------------------------------------------------------------------------

   Next is CPU scheduling statistics. These are simple diffs of /proc/schedstat CPU lines
   along with description. The report also prints % relative to base stat.

   In the example below, schedule() left the CPU0 idle 36.58% of the time. 0.45% of total
   try_to_wake_up() was to wakeup local CPU. And, the total waittime by tasks on CPU0 is
   48.70% of the total runtime by tasks on the same CPU.

   ----------------------------------------------------------------------------------------------------
   CPU 0
   ----------------------------------------------------------------------------------------------------
   DESC                                                                     COUNT   PCT_CHANGE
   ----------------------------------------------------------------------------------------------------
   yld_count                                                        :           0
   array_exp                                                        :           0
   sched_count                                                      :      402267
   sched_goidle                                                     :      147161  (    36.58% )
   ttwu_count                                                       :      236309
   ttwu_local                                                       :        1062  (     0.45% )
   rq_cpu_time                                                      :  7083791148
   run_delay                                                        :  3449973971  (    48.70% )
   pcount                                                           :      255035
   ----------------------------------------------------------------------------------------------------

   Next is load balancing statistics. For each of the sched domains
   (eg: `SMT`, `MC`, `DIE`...), the scheduler computes statistics under
   the following three categories:

   1) Idle Load Balance: Load balancing performed on behalf of a long
                         idling CPU by some other CPU.
   2) Busy Load Balance: Load balancing performed when the CPU was busy.
   3) New Idle Balance : Load balancing performed when a CPU just became
                        idle.

   Under each of these three categories, sched stats report provides
   different load balancing statistics. Along with direct stats, the
   report also contains derived metrics prefixed with *. Example:

   ----------------------------------------------------------------------------------------------------
   CPU 0, DOMAIN SMT CPUS 0,64
   ----------------------------------------------------------------------------------------------------
   DESC                                                                     COUNT    AVG_JIFFIES
   ----------------------------------------- <Category busy> ------------------------------------------
   busy_lb_count                                                    :         136  $       17.08 $
   busy_lb_balanced                                                 :         131  $       17.73 $
   busy_lb_failed                                                   :           0  $        0.00 $
   busy_lb_imbalance_load                                           :          58
   busy_lb_imbalance_util                                           :           0
   busy_lb_imbalance_task                                           :           0
   busy_lb_imbalance_misfit                                         :           0
   busy_lb_gained                                                   :           7
   busy_lb_hot_gained                                               :           0
   busy_lb_nobusyq                                                  :           2  $     1161.50 $
   busy_lb_nobusyg                                                  :         129  $       18.01 $
   *busy_lb_success_count                                           :           5
   *busy_lb_avg_pulled                                              :        1.40
   ----------------------------------------- <Category idle> ------------------------------------------
   idle_lb_count                                                    :         449  $        5.17 $
   idle_lb_balanced                                                 :         382  $        6.08 $
   idle_lb_failed                                                   :           3  $      774.33 $
   idle_lb_imbalance_load                                           :           0
   idle_lb_imbalance_util                                           :           0
   idle_lb_imbalance_task                                           :          71
   idle_lb_imbalance_misfit                                         :           0
   idle_lb_gained                                                   :          67
   idle_lb_hot_gained                                               :           0
   idle_lb_nobusyq                                                  :           0  $        0.00 $
   idle_lb_nobusyg                                                  :         382  $        6.08 $
   *idle_lb_success_count                                           :          64
   *idle_lb_avg_pulled                                              :        1.05
   ---------------------------------------- <Category newidle> ----------------------------------------
   newidle_lb_count                                                 :       30471  $        0.08 $
   newidle_lb_balanced                                              :       28490  $        0.08 $
   newidle_lb_failed                                                :         633  $        3.67 $
   newidle_lb_imbalance_load                                        :           0
   newidle_lb_imbalance_util                                        :           0
   newidle_lb_imbalance_task                                        :        2040
   newidle_lb_imbalance_misfit                                      :           0
   newidle_lb_gained                                                :        1348
   newidle_lb_hot_gained                                            :           0
   newidle_lb_nobusyq                                               :           6  $      387.17 $
   newidle_lb_nobusyg                                               :       26634  $        0.09 $
   *newidle_lb_success_count                                        :        1348
   *newidle_lb_avg_pulled                                           :        1.00
   ----------------------------------------------------------------------------------------------------

   Consider following line:

   newidle_lb_balanced                                              :       28490  $        0.08 $

   While profiling was active, the load-balancer found 28490 times the load
   needs to be balanced on a newly idle CPU 0. Following value encapsulated
   inside $ is average jiffies between two events (2323 / 28490 = 0.08).

   Next are active_load_balance() stats. alb did not trigger while the
   profiling was active, hence it's all 0s.

   --------------------------------- <Category active_load_balance()> ---------------------------------
   alb_count                                                        :           0
   alb_failed                                                       :           0
   alb_pushed                                                       :           0
   ----------------------------------------------------------------------------------------------------

   Next are sched_balance_exec() and sched_balance_fork() stats. They are
   not used but we kept it in RFC just for legacy purpose. Unless opposed,
   we plan to remove them in next revision.

   Next are wakeup statistics. For every domain, the report also shows
   task-wakeup statistics. Example:

   ------------------------------------------ <Wakeup Info> -------------------------------------------
   ttwu_wake_remote                                                 :        1590
   ttwu_move_affine                                                 :          84
   ttwu_move_balance                                                :           0
   ----------------------------------------------------------------------------------------------------

   Same set of stats are reported for each CPU and each domain level.

   How to interpret the diff
   ~~~~~~~~~~~~~~~~~~~~~~~~~

   The `perf sched stats diff` will also start with explaining the columns
   present in the diff. Then it will show the diff in time in terms of
   jiffies. The order of the values depends on the order of input data
   files. It will take `perf.data.old` and `perf.data` respectively as the
   defaults for comparison. Example:

   ----------------------------------------------------------------------------------------------------
   Time elapsed (in jiffies)                                        :        2009,       2001
   ----------------------------------------------------------------------------------------------------

   Below is the sample representing the difference in cpu and domain stats of
   two runs. Here third column or the values enclosed in `|...|` shows the
   percent change between the two. Second and fourth columns shows the
   side-by-side representions of the corresponding fields from `perf sched
   stats report`.

   ----------------------------------------------------------------------------------------------------
   CPU <ALL CPUS SUMMARY>
   ----------------------------------------------------------------------------------------------------
   DESC                                                                    COUNT1      COUNT2   PCT_CHANG>
   ----------------------------------------------------------------------------------------------------
   yld_count                                                        :           0,          0  |     0.00>
   array_exp                                                        :           0,          0  |     0.00>
   sched_count                                                      :      528533,     412573  |   -21.94>
   sched_goidle                                                     :      193426,     146082  |   -24.48>
   ttwu_count                                                       :      313134,     385975  |    23.26>
   ttwu_local                                                       :        1126,       1282  |    13.85>
   rq_cpu_time                                                      :  8257200244, 8301250047  |     0.53>
   run_delay                                                        :  4728347053, 3997100703  |   -15.47>
   pcount                                                           :      335031,     266396  |   -20.49>
   ----------------------------------------------------------------------------------------------------

   Below is the sample of domain stats diff:

   ----------------------------------------------------------------------------------------------------
   CPU <ALL CPUS SUMMARY>, DOMAIN SMT
   ----------------------------------------------------------------------------------------------------
   DESC                                                                    COUNT1      COUNT2   PCT_CHANG>
   ----------------------------------------- <Category busy> ------------------------------------------
   busy_lb_count                                                    :         122,         80  |   -34.43>
   busy_lb_balanced                                                 :         115,         76  |   -33.91>
   busy_lb_failed                                                   :           1,          3  |   200.00>
   busy_lb_imbalance_load                                           :          35,         49  |    40.00>
   busy_lb_imbalance_util                                           :           0,          0  |     0.00>
   busy_lb_imbalance_task                                           :           0,          0  |     0.00>
   busy_lb_imbalance_misfit                                         :           0,          0  |     0.00>
   busy_lb_gained                                                   :           7,          2  |   -71.43>
   busy_lb_hot_gained                                               :           0,          0  |     0.00>
   busy_lb_nobusyq                                                  :           0,          0  |     0.00>
   busy_lb_nobusyg                                                  :         115,         76  |   -33.91>
   *busy_lb_success_count                                           :           6,          1  |   -83.33>
   *busy_lb_avg_pulled                                              :        1.17,       2.00  |    71.43>
   ----------------------------------------- <Category idle> ------------------------------------------
   idle_lb_count                                                    :         568,        620  |     9.15>
   idle_lb_balanced                                                 :         462,        449  |    -2.81>
   idle_lb_failed                                                   :          11,         21  |    90.91>
   idle_lb_imbalance_load                                           :           0,          0  |     0.00>
   idle_lb_imbalance_util                                           :           0,          0  |     0.00>
   idle_lb_imbalance_task                                           :         115,        189  |    64.35>
   idle_lb_imbalance_misfit                                         :           0,          0  |     0.00>
   idle_lb_gained                                                   :         103,        169  |    64.08>
   idle_lb_hot_gained                                               :           0,          0  |     0.00>
   idle_lb_nobusyq                                                  :           0,          0  |     0.00>
   idle_lb_nobusyg                                                  :         462,        449  |    -2.81>
   *idle_lb_success_count                                           :          95,        150  |    57.89>
   *idle_lb_avg_pulled                                              :        1.08,       1.13  |     3.92>
   ---------------------------------------- <Category newidle> ----------------------------------------
   newidle_lb_count                                                 :       16961,       3155  |   -81.40>
   newidle_lb_balanced                                              :       15646,       2556  |   -83.66>
   newidle_lb_failed                                                :         397,        142  |   -64.23>
   newidle_lb_imbalance_load                                        :           0,          0  |     0.00>
   newidle_lb_imbalance_util                                        :           0,          0  |     0.00>
   newidle_lb_imbalance_task                                        :        1376,        655  |   -52.40>
   newidle_lb_imbalance_misfit                                      :           0,          0  |     0.00>
   newidle_lb_gained                                                :         917,        457  |   -50.16>
   newidle_lb_hot_gained                                            :           0,          0  |     0.00>
   newidle_lb_nobusyq                                               :           3,          1  |   -66.67>
   newidle_lb_nobusyg                                               :       14480,       2103  |   -85.48>
   *newidle_lb_success_count                                        :         918,        457  |   -50.22>
   *newidle_lb_avg_pulled                                           :        1.00,       1.00  |     0.11>
   --------------------------------- <Category active_load_balance()> ---------------------------------
   alb_count                                                        :           0,          1  |     0.00>
   alb_failed                                                       :           0,          0  |     0.00>
   alb_pushed                                                       :           0,          1  |     0.00>
   --------------------------------- <Category sched_balance_exec()> ----------------------------------
   sbe_count                                                        :           0,          0  |     0.00>
   sbe_balanced                                                     :           0,          0  |     0.00>
   sbe_pushed                                                       :           0,          0  |     0.00>
   --------------------------------- <Category sched_balance_fork()> ----------------------------------
   sbf_count                                                        :           0,          0  |     0.00>
   sbf_balanced                                                     :           0,          0  |     0.00>
   sbf_pushed                                                       :           0,          0  |     0.00>
   ------------------------------------------ <Wakeup Info> -------------------------------------------
   ttwu_wake_remote                                                 :        2031,       2914  |    43.48>
   ttwu_move_affine                                                 :          73,        124  |    69.86>
   ttwu_move_balance                                                :           0,          0  |     0.00>
   ----------------------------------------------------------------------------------------------------

OPTIONS
-------
Applicable to {record|latency|map|replay|script}

-i::
--input=<file>::
        Input file name. (default: perf.data unless stdin is a fifo)

-v::
--verbose::
        Be more verbose. (show symbol address, etc)

-D::
--dump-raw-trace=::
        Display verbose dump of the sched data.

-f::
--force::
	Don't complain, do it.

OPTIONS for 'perf sched latency'
-------------------------------

-C::
--CPU <n>::
        CPU to profile on.

-p::
--pids::
        latency stats per pid instead of per command name.

-s::
--sort <key[,key2...]>::
        sort by key(s): runtime, switch, avg, max
        by default it's sorted by "avg ,max ,switch ,runtime".

OPTIONS for 'perf sched map'
----------------------------

--compact::
	Show only CPUs with activity. Helps visualizing on high core
	count systems.

--cpus::
	Show just entries with activities for the given CPUs.

--color-cpus::
	Highlight the given cpus.

--color-pids::
	Highlight the given pids.

--task-name <task>::
	Map output only for the given task name(s). Separate the
	task names with a comma (without whitespace). The sched-out
	time is printed and is represented by '*-' for the given
	task name(s).
	('-' indicates other tasks while '.' is idle).

--fuzzy-name::
	Given task name(s) can be partially matched (fuzzy matching).

OPTIONS for 'perf sched timehist'
---------------------------------
-k::
--vmlinux=<file>::
    vmlinux pathname

--kallsyms=<file>::
    kallsyms pathname

-g::
--call-graph::
	Display call chains if present (default on).

--max-stack::
	Maximum number of functions to display in backtrace, default 5.

-C=::
--cpu=::
	Only show events for the given CPU(s) (comma separated list).

-p=::
--pid=::
	Only show events for given process ID (comma separated list).

-t=::
--tid=::
	Only show events for given thread ID (comma separated list).

-s::
--summary::
    Show only a summary of scheduling by thread with min, max, and average
    run times (in sec) and relative stddev.

-S::
--with-summary::
    Show all scheduling events followed by a summary by thread with min,
    max, and average run times (in sec) and relative stddev.

--symfs=<directory[,layout]>::
        Look for files with symbols relative to this directory. The optional
        layout can be 'hierarchy' (default, matches full path) or 'flat'
        (only matches base name). This is useful when debug files are stored
        in a flat directory structure.

-V::
--cpu-visual::
	Show visual aid for sched switches by CPU: 'i' marks idle time,
	's' are scheduler events.

-w::
--wakeups::
	Show wakeup events.

-M::
--migrations::
	Show migration events.

-n::
--next::
	Show next task.

-I::
--idle-hist::
	Show idle-related events only.

--time::
	Only analyze samples within given time window: <start>,<stop>. Times
	have the format seconds.microseconds. If start is not given (i.e., time
	string is ',x.y') then analysis starts at the beginning of the file. If
	stop time is not given (i.e, time string is 'x.y,') then analysis goes
	to end of file.

--state::
	Show task state when it switched out.

--show-prio::
	Show task priority.

--prio::
	Only show events for given task priority(ies). Multiple priorities can be
	provided as a comma-separated list with no spaces: 0,120. Ranges of
	priorities are specified with -: 120-129. A combination of both can also be
	provided: 0,120-129.

-P::
--pre-migrations::
	Show pre-migration wait time. pre-migration wait time is the time spent
	by a task waiting on a runqueue but not getting the chance to run there
	and is migrated to a different runqueue where it is finally run. This
	time between sched_wakeup and migrate_task is the pre-migration wait
	time.

OPTIONS for 'perf sched replay'
------------------------------

-r::
--repeat <n>::
	repeat the workload n times (0: infinite). Default is 10.

SEE ALSO
--------
linkperf:perf-record[1]
