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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.rain.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 1 2 3 4 5 6 7 8 9 10 11 12

NOTE: In the sched_yield() statistics, the active queue is considered empty

    if it has only one process in it, since obviously the process calling

    sched_yield() is that process.

First four fields are sched_yield() statistics:

     1) # of times both the active and the expired queue were empty

     2) # of times just the active queue was empty

     3) # of times just the expired queue was empty

     4) # of times sched_yield() was called

Next three are schedule() statistics:

     5) # of times we switched to the expired queue and reused it

     6) # of times schedule() was called

     7) # of times schedule() left the processor idle

Next two are try_to_wake_up() statistics:

     8) # of times try_to_wake_up() was called

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

Next three are statistics describing scheduling latency:

    10) sum of all time spent running by tasks on this processor (in jiffies)

    11) sum of all time spent waiting to run by tasks on this processor (in

        jiffies)

    12) # 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  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//schedstat

----------------

schedstats also adds a new /proc/

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

     2) time spent waiting on a runqueue

     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.rain.com/rick/linux/schedstat/v12/latency.c