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diff --git a/Documentation/scheduler/sched-stats.rst b/Documentation/scheduler/sched-stats.rst new file mode 100644 index 000000000000..9d6a337755f4 --- /dev/null +++ b/Documentation/scheduler/sched-stats.rst @@ -0,0 +1,205 @@ +==================== +Scheduler Statistics +==================== + +Version 17 of schedstats removed 'lb_imbalance' field as it has no +significance anymore and instead added more relevant fields namely +'lb_imbalance_load', 'lb_imbalance_util', 'lb_imbalance_task' and +'lb_imbalance_misfit'. The domain field prints the name of the +corresponding sched domain from this version onwards. + +Version 16 of schedstats changed the order of definitions within +'enum cpu_idle_type', which changed the order of [CPU_MAX_IDLE_TYPES] +columns in show_schedstat(). In particular the position of CPU_IDLE +and __CPU_NOT_IDLE changed places. The size of the array is unchanged. + +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. Details are available at + + https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/scheduler/sched-stats.txt?id=1e1dbb259c79b + +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. Details are available at + + https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/sched-stats.txt?id=b762f3ffb797c + +The schedstat documentation is maintained version 10 onwards and is not +updated for version 11 and 12. The details for version 10 are available at + + https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/sched-stats.txt?id=1da177e4c3f4 + +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> <name> <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 37 38 39 40 41 42 43 44 45 + +The <name> field prints the name of the sched domain and is only supported +with schedstat version >= 17. On previous versions, <cpumask> is the first +field. + +The <cpumask> field is a bit mask indicating what cpus this domain operates +over. + +The next 33 are a variety of sched_balance_rq() statistics in grouped into types +of idleness (busy, idle and newly idle): + + 1) # of times in this domain sched_balance_rq() was called when the + cpu was busy + 2) # of times in this domain sched_balance_rq() checked but found the + load did not require balancing when busy + 3) # of times in this domain sched_balance_rq() tried to move one or + more tasks and failed, when the cpu was busy + 4) Total imbalance in load in this domain when the cpu was busy + 5) Total imbalance in utilization in this domain when the cpu was busy + 6) Total imbalance in number of tasks in this domain when the cpu was busy + 7) Total imbalance due to misfit tasks in this domain when the cpu was + busy + 8) # of times in this domain detach_task() was called when busy + 9) # of times in this domain detach_task() was called even though the + target task was cache-hot when busy + 10) # of times in this domain sched_balance_rq() was called but did not + find a busier queue while the cpu was busy + 11) # of times in this domain a busier queue was found while the cpu + was busy but no busier group was found + + 12) # of times in this domain sched_balance_rq() was called when the + cpu was idle + 13) # of times in this domain sched_balance_rq() checked but found + the load did not require balancing when the cpu was idle + 14) # of times in this domain sched_balance_rq() tried to move one or + more tasks and failed, when the cpu was idle + 15) Total imbalance in load in this domain when the cpu was idle + 16) Total imbalance in utilization in this domain when the cpu was idle + 17) Total imbalance in number of tasks in this domain when the cpu was idle + 18) Total imbalance due to misfit tasks in this domain when the cpu was + idle + 19) # of times in this domain detach_task() was called when the cpu + was idle + 20) # of times in this domain detach_task() was called even though + the target task was cache-hot when idle + 21) # of times in this domain sched_balance_rq() was called but did + not find a busier queue while the cpu was idle + 22) # of times in this domain a busier queue was found while the + cpu was idle but no busier group was found + + 23) # of times in this domain sched_balance_rq() was called when the + cpu was just becoming idle + 24) # of times in this domain sched_balance_rq() checked but found the + load did not require balancing when the cpu was just becoming idle + 25) # of times in this domain sched_balance_rq() tried to move one or more + tasks and failed, when the cpu was just becoming idle + 26) Total imbalance in load in this domain when the cpu was just becoming + idle + 27) Total imbalance in utilization in this domain when the cpu was just + becoming idle + 28) Total imbalance in number of tasks in this domain when the cpu was just + becoming idle + 29) Total imbalance due to misfit tasks in this domain when the cpu was + just becoming idle + 30) # of times in this domain detach_task() was called when newly idle + 31) # of times in this domain detach_task() was called even though the + target task was cache-hot when just becoming idle + 32) # of times in this domain sched_balance_rq() was called but did not + find a busier queue while the cpu was just becoming idle + 33) # 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: + + 34) # of times active_load_balance() was called + 35) # of times active_load_balance() tried to move a task and failed + 36) # of times active_load_balance() successfully moved a task + + Next three are sched_balance_exec() statistics: + + 37) sbe_cnt is not used + 38) sbe_balanced is not used + 39) sbe_pushed is not used + + Next three are sched_balance_fork() statistics: + + 40) sbf_cnt is not used + 41) sbf_balanced is not used + 42) sbf_pushed is not used + + Next three are try_to_wake_up() statistics: + + 43) # of times in this domain try_to_wake_up() awoke a task that + last ran on a different cpu in this domain + 44) # 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 + 45) # 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 |