FreeBSD/Linux Kernel Cross Reference
sys/Documentation/sched-stats.txt

     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<N> 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<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
        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

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