168 lines
7.4 KiB
ReStructuredText
168 lines
7.4 KiB
ReStructuredText
====================
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Scheduler Statistics
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====================
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Version 15 of schedstats dropped counters for some sched_yield:
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yld_exp_empty, yld_act_empty and yld_both_empty. Otherwise, it is
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identical to version 14.
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Version 14 of schedstats includes support for sched_domains, which hit the
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mainline kernel in 2.6.20 although it is identical to the stats from version
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12 which was in the kernel from 2.6.13-2.6.19 (version 13 never saw a kernel
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release). Some counters make more sense to be per-runqueue; other to be
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per-domain. Note that domains (and their associated information) will only
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be pertinent and available on machines utilizing CONFIG_SMP.
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In version 14 of schedstat, there is at least one level of domain
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statistics for each cpu listed, and there may well be more than one
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domain. Domains have no particular names in this implementation, but
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the highest numbered one typically arbitrates balancing across all the
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cpus on the machine, while domain0 is the most tightly focused domain,
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sometimes balancing only between pairs of cpus. At this time, there
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are no architectures which need more than three domain levels. The first
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field in the domain stats is a bit map indicating which cpus are affected
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by that domain.
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These fields are counters, and only increment. Programs which make use
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of these will need to start with a baseline observation and then calculate
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the change in the counters at each subsequent observation. A perl script
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which does this for many of the fields is available at
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http://eaglet.pdxhosts.com/rick/linux/schedstat/
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Note that any such script will necessarily be version-specific, as the main
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reason to change versions is changes in the output format. For those wishing
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to write their own scripts, the fields are described here.
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CPU statistics
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--------------
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cpu<N> 1 2 3 4 5 6 7 8 9
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First field is a sched_yield() statistic:
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1) # of times sched_yield() was called
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Next three are schedule() statistics:
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2) This field is a legacy array expiration count field used in the O(1)
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scheduler. We kept it for ABI compatibility, but it is always set to zero.
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3) # of times schedule() was called
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4) # of times schedule() left the processor idle
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Next two are try_to_wake_up() statistics:
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5) # of times try_to_wake_up() was called
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6) # of times try_to_wake_up() was called to wake up the local cpu
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Next three are statistics describing scheduling latency:
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7) sum of all time spent running by tasks on this processor (in nanoseconds)
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8) sum of all time spent waiting to run by tasks on this processor (in
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nanoseconds)
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9) # of timeslices run on this cpu
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Domain statistics
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-----------------
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One of these is produced per domain for each cpu described. (Note that if
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CONFIG_SMP is not defined, *no* domains are utilized and these lines
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will not appear in the output.)
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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
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The first field is a bit mask indicating what cpus this domain operates over.
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The next 24 are a variety of load_balance() statistics in grouped into types
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of idleness (idle, busy, and newly idle):
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1) # of times in this domain load_balance() was called when the
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cpu was idle
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2) # of times in this domain load_balance() checked but found
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the load did not require balancing when the cpu was idle
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3) # of times in this domain load_balance() tried to move one or
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more tasks and failed, when the cpu was idle
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4) sum of imbalances discovered (if any) with each call to
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load_balance() in this domain when the cpu was idle
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5) # of times in this domain pull_task() was called when the cpu
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was idle
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6) # of times in this domain pull_task() was called even though
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the target task was cache-hot when idle
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7) # of times in this domain load_balance() was called but did
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not find a busier queue while the cpu was idle
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8) # of times in this domain a busier queue was found while the
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cpu was idle but no busier group was found
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9) # of times in this domain load_balance() was called when the
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cpu was busy
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10) # of times in this domain load_balance() checked but found the
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load did not require balancing when busy
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11) # of times in this domain load_balance() tried to move one or
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more tasks and failed, when the cpu was busy
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12) sum of imbalances discovered (if any) with each call to
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load_balance() in this domain when the cpu was busy
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13) # of times in this domain pull_task() was called when busy
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14) # of times in this domain pull_task() was called even though the
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target task was cache-hot when busy
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15) # of times in this domain load_balance() was called but did not
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find a busier queue while the cpu was busy
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16) # of times in this domain a busier queue was found while the cpu
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was busy but no busier group was found
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17) # of times in this domain load_balance() was called when the
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cpu was just becoming idle
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18) # of times in this domain load_balance() checked but found the
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load did not require balancing when the cpu was just becoming idle
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19) # of times in this domain load_balance() tried to move one or more
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tasks and failed, when the cpu was just becoming idle
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20) sum of imbalances discovered (if any) with each call to
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load_balance() in this domain when the cpu was just becoming idle
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21) # of times in this domain pull_task() was called when newly idle
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22) # of times in this domain pull_task() was called even though the
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target task was cache-hot when just becoming idle
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23) # of times in this domain load_balance() was called but did not
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find a busier queue while the cpu was just becoming idle
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24) # of times in this domain a busier queue was found while the cpu
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was just becoming idle but no busier group was found
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Next three are active_load_balance() statistics:
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25) # of times active_load_balance() was called
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26) # of times active_load_balance() tried to move a task and failed
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27) # of times active_load_balance() successfully moved a task
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Next three are sched_balance_exec() statistics:
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28) sbe_cnt is not used
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29) sbe_balanced is not used
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30) sbe_pushed is not used
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Next three are sched_balance_fork() statistics:
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31) sbf_cnt is not used
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32) sbf_balanced is not used
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33) sbf_pushed is not used
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Next three are try_to_wake_up() statistics:
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34) # of times in this domain try_to_wake_up() awoke a task that
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last ran on a different cpu in this domain
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35) # of times in this domain try_to_wake_up() moved a task to the
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waking cpu because it was cache-cold on its own cpu anyway
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36) # of times in this domain try_to_wake_up() started passive balancing
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/proc/<pid>/schedstat
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---------------------
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schedstats also adds a new /proc/<pid>/schedstat file to include some of
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the same information on a per-process level. There are three fields in
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this file correlating for that process to:
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1) time spent on the cpu (in nanoseconds)
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2) time spent waiting on a runqueue (in nanoseconds)
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3) # of timeslices run on this cpu
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A program could be easily written to make use of these extra fields to
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report on how well a particular process or set of processes is faring
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under the scheduler's policies. A simple version of such a program is
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available at
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http://eaglet.pdxhosts.com/rick/linux/schedstat/v12/latency.c
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