On Wed, Jul 18, 2007 at 11:11:30AM +0200, Joachim Deguara wrote:
> While learning about schedstats I found that the documentation in the tree is
> old. I updated it and found some interesting stuff like schedstats version
> 14 is the same as version and version 13 never saw a kernel release! Also
> there are 6 fields in the current schedstats that are not used anymore. Nick
> had made them irrelevant in commit 476d139c218e44e045e4bc6d4cc02b010b343939
> but never removed them.
>
> Thanks to Rick's perl script who I borrowed some of the updated descriptions
> from.
Ah, thanks, I actually didn't realise there was such good documentation
there. Patch looks good.
BTW. I have a simple program to do a basic statistical summary of the
multiprocessor balancing if you are interested and haven't seen it.
Acked-by: Nick Piggin <[email protected]>
>
> -Joachim
>
> --
> Updating schedstats documentation from version 10 to 14.
>
> Signed-off-by: Joachim Deguara <[email protected]>
>
> Index: kernel/Documentation/sched-stats.txt
> ===================================================================
> --- kernel.orig/Documentation/sched-stats.txt
> +++ kernel/Documentation/sched-stats.txt
> @@ -1,10 +1,11 @@
> -Version 10 of schedstats includes support for sched_domains, which
> -hit the mainline kernel in 2.6.7. 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.
> +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 10 of schedstat, there is at least one level of domain
> +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
> @@ -27,7 +28,7 @@ to write their own scripts, the fields a
>
> CPU statistics
> --------------
> -cpu<N> 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
> +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
> @@ -39,48 +40,20 @@ First four fields are sched_yield() stat
> 3) # of times just the expired queue was empty
> 4) # of times sched_yield() was called
>
> -Next four are schedule() statistics:
> - 5) # of times the active queue had at least one other process on it
> - 6) # of times we switched to the expired queue and reused it
> - 7) # of times schedule() was called
> - 8) # of times schedule() left the processor idle
> -
> -Next four are active_load_balance() statistics:
> - 9) # of times active_load_balance() was called
> - 10) # of times active_load_balance() caused this cpu to gain a task
> - 11) # of times active_load_balance() caused this cpu to lose a task
> - 12) # of times active_load_balance() tried to move a task and failed
> -
> -Next three are try_to_wake_up() statistics:
> - 13) # of times try_to_wake_up() was called
> - 14) # of times try_to_wake_up() successfully moved the awakening task
> - 15) # of times try_to_wake_up() attempted to move the awakening task
> -
> -Next two are wake_up_new_task() statistics:
> - 16) # of times wake_up_new_task() was called
> - 17) # of times wake_up_new_task() successfully moved the new task
> +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 one is a sched_migrate_task() statistic:
> - 18) # of times sched_migrate_task() was called
> -
> -Next one is a sched_balance_exec() statistic:
> - 19) # of times sched_balance_exec() was called
> +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:
> - 20) sum of all time spent running by tasks on this processor (in ms)
> - 21) sum of all time spent waiting to run by tasks on this processor (in
> ms)
> - 22) # of tasks (not necessarily unique) given to the processor
> -
> -The last six are statistics dealing with pull_task():
> - 23) # of times pull_task() moved a task to this cpu when newly idle
> - 24) # of times pull_task() stole a task from this cpu when another cpu
> - was newly idle
> - 25) # of times pull_task() moved a task to this cpu when idle
> - 26) # of times pull_task() stole a task from this cpu when another cpu
> - was idle
> - 27) # of times pull_task() moved a task to this cpu when busy
> - 28) # of times pull_task() stole a task from this cpu when another cpu
> - was busy
> + 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
> @@ -89,65 +62,95 @@ One of these is produced per domain for
> CONFIG_SMP is not defined, *no* domains are utilized and these lines
> will not appear in the output.)
>
> -domain<N> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
> +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 fifteen are a variety of load_balance() statistics:
> -
> - 1) # of times in this domain load_balance() was called when the cpu
> - was idle
> - 2) # of times in this domain load_balance() was called when the cpu
> - was busy
> - 3) # of times in this domain load_balance() was called when the cpu
> - was just becoming idle
> - 4) # of times in this domain load_balance() tried to move one or more
> - tasks and failed, when the cpu was idle
> - 5) # of times in this domain load_balance() tried to move one or more
> - tasks and failed, when the cpu was busy
> - 6) # of times in this domain load_balance() tried to move one or more
> - tasks and failed, when the cpu was just becoming idle
> - 7) sum of imbalances discovered (if any) with each call to
> - load_balance() in this domain when the cpu was idle
> - 8) sum of imbalances discovered (if any) with each call to
> - load_balance() in this domain when the cpu was busy
> - 9) sum of imbalances discovered (if any) with each call to
> - load_balance() in this domain when the cpu was just becoming idle
> - 10) # of times in this domain load_balance() was called but did not find
> - a busier queue while the cpu was idle
> - 11) # of times in this domain load_balance() was called but did not find
> - a busier queue while the cpu was busy
> - 12) # of times in this domain load_balance() was called but did not find
> - a busier queue while the cpu was just becoming idle
> - 13) # of times in this domain a busier queue was found while the cpu was
> - idle but no busier group was found
> - 14) # of times in this domain a busier queue was found while the cpu was
> - busy but no busier group was found
> - 15) # of times in this domain a busier queue was found while the cpu was
> - just becoming idle but no busier group was found
> -
> -Next two are sched_balance_exec() statistics:
> - 17) # of times in this domain sched_balance_exec() successfully pushed
> - a task to a new cpu
> - 18) # of times in this domain sched_balance_exec() tried but failed to
> - push a task to a new cpu
> -
> -Next two are try_to_wake_up() statistics:
> - 19) # of times in this domain try_to_wake_up() tried to move a task based
> - on affinity and cache warmth
> - 20) # of times in this domain try_to_wake_up() tried to move a task based
> - on load balancing
> +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 to fields 20, 21, and 22 in the CPU fields, but
> -they only apply for that process.
> +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/v10/latency.c
> + http://eaglet.rain.com/rick/linux/schedstat/v12/latency.c
>
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