Documentation/scheduler/sched-stats.rst - third_party/linux - Git at Google

 ====================
 Scheduler Statistics
 ====================

 Version 15 of schedstats dropped counters for some sched_yield:
 yld_exp_empty, yld_act_empty and yld_both_empty. Otherwise, it is
 identical to version 14.

 Version 14 of schedstats includes support for sched_domains, which hit the
 mainline kernel in 2.6.20 although it is identical to the stats from version
 12 which was in the kernel from 2.6.13-2.6.19 (version 13 never saw a kernel
 release).  Some counters make more sense to be per-runqueue; other to be
 per-domain.  Note that domains (and their associated information) will only
 be pertinent and available on machines utilizing CONFIG_SMP.

 In version 14 of schedstat, there is at least one level of domain
 statistics for each cpu listed, and there may well be more than one
 domain.  Domains have no particular names in this implementation, but
 the highest numbered one typically arbitrates balancing across all the
 cpus on the machine, while domain0 is the most tightly focused domain,
 sometimes balancing only between pairs of cpus.  At this time, there
 are no architectures which need more than three domain levels. The first
 field in the domain stats is a bit map indicating which cpus are affected
 by that domain.

 These fields are counters, and only increment.  Programs which make use
 of these will need to start with a baseline observation and then calculate
 the change in the counters at each subsequent observation.  A perl script
 which does this for many of the fields is available at

     http://eaglet.pdxhosts.com/rick/linux/schedstat/

 Note that any such script will necessarily be version-specific, as the main
 reason to change versions is changes in the output format.  For those wishing
 to write their own scripts, the fields are described here.

 CPU statistics
 --------------
 cpu<N> 1 2 3 4 5 6 7 8 9

 First field is a sched_yield() statistic:

      1) # of times sched_yield() was called

 Next three are schedule() statistics:

      2) This field is a legacy array expiration count field used in the O(1)
 	scheduler. We kept it for ABI compatibility, but it is always set to zero.
      3) # of times schedule() was called
      4) # of times schedule() left the processor idle

 Next two are try_to_wake_up() statistics:

      5) # of times try_to_wake_up() was called
      6) # of times try_to_wake_up() was called to wake up the local cpu

 Next three are statistics describing scheduling latency:

      7) sum of all time spent running by tasks on this processor (in nanoseconds)
      8) sum of all time spent waiting to run by tasks on this processor (in
         nanoseconds)
      9) # of timeslices run on this cpu


 Domain statistics
 -----------------
 One of these is produced per domain for each cpu described. (Note that if
 CONFIG_SMP is not defined, *no* domains are utilized and these lines
 will not appear in the output.)

 domain<N> <cpumask> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

 The first field is a bit mask indicating what cpus this domain operates over.

 The next 24 are a variety of load_balance() statistics in grouped into types
 of idleness (idle, busy, and newly idle):

     1)  # of times in this domain load_balance() was called when the
         cpu was idle
     2)  # of times in this domain load_balance() checked but found
         the load did not require balancing when the cpu was idle
     3)  # of times in this domain load_balance() tried to move one or
         more tasks and failed, when the cpu was idle
     4)  sum of imbalances discovered (if any) with each call to
         load_balance() in this domain when the cpu was idle
     5)  # of times in this domain pull_task() was called when the cpu
         was idle
     6)  # of times in this domain pull_task() was called even though
         the target task was cache-hot when idle
     7)  # of times in this domain load_balance() was called but did
         not find a busier queue while the cpu was idle
     8)  # of times in this domain a busier queue was found while the
         cpu was idle but no busier group was found
     9)  # of times in this domain load_balance() was called when the
         cpu was busy
     10) # of times in this domain load_balance() checked but found the
         load did not require balancing when busy
     11) # of times in this domain load_balance() tried to move one or
         more tasks and failed, when the cpu was busy
     12) sum of imbalances discovered (if any) with each call to
         load_balance() in this domain when the cpu was busy
     13) # of times in this domain pull_task() was called when busy
     14) # of times in this domain pull_task() was called even though the
         target task was cache-hot when busy
     15) # of times in this domain load_balance() was called but did not
         find a busier queue while the cpu was busy
     16) # of times in this domain a busier queue was found while the cpu
         was busy but no busier group was found

     17) # of times in this domain load_balance() was called when the
         cpu was just becoming idle
     18) # of times in this domain load_balance() checked but found the
         load did not require balancing when the cpu was just becoming idle
     19) # of times in this domain load_balance() tried to move one or more
         tasks and failed, when the cpu was just becoming idle
     20) sum of imbalances discovered (if any) with each call to
         load_balance() in this domain when the cpu was just becoming idle
     21) # of times in this domain pull_task() was called when newly idle
     22) # of times in this domain pull_task() was called even though the
         target task was cache-hot when just becoming idle
     23) # of times in this domain load_balance() was called but did not
         find a busier queue while the cpu was just becoming idle
     24) # of times in this domain a busier queue was found while the cpu
         was just becoming idle but no busier group was found

    Next three are active_load_balance() statistics:

     25) # of times active_load_balance() was called
     26) # of times active_load_balance() tried to move a task and failed
     27) # of times active_load_balance() successfully moved a task

    Next three are sched_balance_exec() statistics:

     28) sbe_cnt is not used
     29) sbe_balanced is not used
     30) sbe_pushed is not used

    Next three are sched_balance_fork() statistics:

     31) sbf_cnt is not used
     32) sbf_balanced is not used
     33) sbf_pushed is not used

    Next three are try_to_wake_up() statistics:

     34) # of times in this domain try_to_wake_up() awoke a task that
         last ran on a different cpu in this domain
     35) # of times in this domain try_to_wake_up() moved a task to the
         waking cpu because it was cache-cold on its own cpu anyway
     36) # of times in this domain try_to_wake_up() started passive balancing

 /proc/<pid>/schedstat
 ---------------------
 schedstats also adds a new /proc/<pid>/schedstat file to include some of
 the same information on a per-process level.  There are three fields in
 this file correlating for that process to:

      1) time spent on the cpu (in nanoseconds)
      2) time spent waiting on a runqueue (in nanoseconds)
      3) # of timeslices run on this cpu

 A program could be easily written to make use of these extra fields to
 report on how well a particular process or set of processes is faring
 under the scheduler's policies.  A simple version of such a program is
 available at

     http://eaglet.pdxhosts.com/rick/linux/schedstat/v12/latency.c
	====================
	Scheduler Statistics
	====================

	Version 15 of schedstats dropped counters for some sched_yield:
	yld_exp_empty, yld_act_empty and yld_both_empty. Otherwise, it is
	identical to version 14.

	Version 14 of schedstats includes support for sched_domains, which hit the
	mainline kernel in 2.6.20 although it is identical to the stats from version
	12 which was in the kernel from 2.6.13-2.6.19 (version 13 never saw a kernel
	release). Some counters make more sense to be per-runqueue; other to be
	per-domain. Note that domains (and their associated information) will only
	be pertinent and available on machines utilizing CONFIG_SMP.

	In version 14 of schedstat, there is at least one level of domain
	statistics for each cpu listed, and there may well be more than one
	domain. Domains have no particular names in this implementation, but
	the highest numbered one typically arbitrates balancing across all the
	cpus on the machine, while domain0 is the most tightly focused domain,
	sometimes balancing only between pairs of cpus. At this time, there
	are no architectures which need more than three domain levels. The first
	field in the domain stats is a bit map indicating which cpus are affected
	by that domain.

	These fields are counters, and only increment. Programs which make use
	of these will need to start with a baseline observation and then calculate
	the change in the counters at each subsequent observation. A perl script
	which does this for many of the fields is available at

	http://eaglet.pdxhosts.com/rick/linux/schedstat/

	Note that any such script will necessarily be version-specific, as the main
	reason to change versions is changes in the output format. For those wishing
	to write their own scripts, the fields are described here.

	CPU statistics
	--------------
	cpu<N> 1 2 3 4 5 6 7 8 9

	First field is a sched_yield() statistic:

	1) # of times sched_yield() was called

	Next three are schedule() statistics:

	2) This field is a legacy array expiration count field used in the O(1)
	scheduler. We kept it for ABI compatibility, but it is always set to zero.
	3) # of times schedule() was called
	4) # of times schedule() left the processor idle

	Next two are try_to_wake_up() statistics:

	5) # of times try_to_wake_up() was called
	6) # of times try_to_wake_up() was called to wake up the local cpu

	Next three are statistics describing scheduling latency:

	7) sum of all time spent running by tasks on this processor (in nanoseconds)
	8) sum of all time spent waiting to run by tasks on this processor (in
	nanoseconds)
	9) # of timeslices run on this cpu


	Domain statistics
	-----------------
	One of these is produced per domain for each cpu described. (Note that if
	CONFIG_SMP is not defined, no domains are utilized and these lines
	will not appear in the output.)

	domain<N> <cpumask> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

	The first field is a bit mask indicating what cpus this domain operates over.

	The next 24 are a variety of load_balance() statistics in grouped into types
	of idleness (idle, busy, and newly idle):

	1) # of times in this domain load_balance() was called when the
	cpu was idle
	2) # of times in this domain load_balance() checked but found
	the load did not require balancing when the cpu was idle
	3) # of times in this domain load_balance() tried to move one or
	more tasks and failed, when the cpu was idle
	4) sum of imbalances discovered (if any) with each call to
	load_balance() in this domain when the cpu was idle
	5) # of times in this domain pull_task() was called when the cpu
	was idle
	6) # of times in this domain pull_task() was called even though
	the target task was cache-hot when idle
	7) # of times in this domain load_balance() was called but did
	not find a busier queue while the cpu was idle
	8) # of times in this domain a busier queue was found while the
	cpu was idle but no busier group was found
	9) # of times in this domain load_balance() was called when the
	cpu was busy
	10) # of times in this domain load_balance() checked but found the
	load did not require balancing when busy
	11) # of times in this domain load_balance() tried to move one or
	more tasks and failed, when the cpu was busy
	12) sum of imbalances discovered (if any) with each call to
	load_balance() in this domain when the cpu was busy
	13) # of times in this domain pull_task() was called when busy
	14) # of times in this domain pull_task() was called even though the
	target task was cache-hot when busy
	15) # of times in this domain load_balance() was called but did not
	find a busier queue while the cpu was busy
	16) # of times in this domain a busier queue was found while the cpu
	was busy but no busier group was found

	17) # of times in this domain load_balance() was called when the
	cpu was just becoming idle
	18) # of times in this domain load_balance() checked but found the
	load did not require balancing when the cpu was just becoming idle
	19) # of times in this domain load_balance() tried to move one or more
	tasks and failed, when the cpu was just becoming idle
	20) sum of imbalances discovered (if any) with each call to
	load_balance() in this domain when the cpu was just becoming idle
	21) # of times in this domain pull_task() was called when newly idle
	22) # of times in this domain pull_task() was called even though the
	target task was cache-hot when just becoming idle
	23) # of times in this domain load_balance() was called but did not
	find a busier queue while the cpu was just becoming idle
	24) # of times in this domain a busier queue was found while the cpu
	was just becoming idle but no busier group was found

	Next three are active_load_balance() statistics:

	25) # of times active_load_balance() was called
	26) # of times active_load_balance() tried to move a task and failed
	27) # of times active_load_balance() successfully moved a task

	Next three are sched_balance_exec() statistics:

	28) sbe_cnt is not used
	29) sbe_balanced is not used
	30) sbe_pushed is not used

	Next three are sched_balance_fork() statistics:

	31) sbf_cnt is not used
	32) sbf_balanced is not used
	33) sbf_pushed is not used

	Next three are try_to_wake_up() statistics:

	34) # of times in this domain try_to_wake_up() awoke a task that
	last ran on a different cpu in this domain
	35) # of times in this domain try_to_wake_up() moved a task to the
	waking cpu because it was cache-cold on its own cpu anyway
	36) # of times in this domain try_to_wake_up() started passive balancing

	/proc/<pid>/schedstat
	---------------------
	schedstats also adds a new /proc/<pid>/schedstat file to include some of
	the same information on a per-process level. There are three fields in
	this file correlating for that process to:

	1) time spent on the cpu (in nanoseconds)
	2) time spent waiting on a runqueue (in nanoseconds)
	3) # of timeslices run on this cpu

	A program could be easily written to make use of these extra fields to
	report on how well a particular process or set of processes is faring
	under the scheduler's policies. A simple version of such a program is
	available at

	http://eaglet.pdxhosts.com/rick/linux/schedstat/v12/latency.c