Messages in this thread Patch in this message | | | Date | Wed, 13 Nov 2013 09:25:41 -0800 | From | tip-bot for Peter Zijlstra <> | Subject | [tip:sched/urgent] sched: Optimize task_sched_runtime() |
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Commit-ID: 911b2898b3c9fe0048e9485ad1629ed4fce330fd Gitweb: http://git.kernel.org/tip/911b2898b3c9fe0048e9485ad1629ed4fce330fd Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Mon, 11 Nov 2013 18:21:56 +0100 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 13 Nov 2013 13:33:54 +0100
sched: Optimize task_sched_runtime()
Large multi-threaded apps like to hit this using do_sys_times() and then queue up on the rq->lock.
Avoid when possible.
Larry reported ~20% performance increase his test case.
Reported-by: Larry Woodman <lwoodman@redhat.com> Suggested-by: Paul Turner <pjt@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/20131111172925.GG26898@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/sched/core.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 1deccd7..c180860 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2253,6 +2253,20 @@ unsigned long long task_sched_runtime(struct task_struct *p) struct rq *rq; u64 ns = 0; +#if defined(CONFIG_64BIT) && defined(CONFIG_SMP) + /* + * 64-bit doesn't need locks to atomically read a 64bit value. + * So we have a optimization chance when the task's delta_exec is 0. + * Reading ->on_cpu is racy, but this is ok. + * + * If we race with it leaving cpu, we'll take a lock. So we're correct. + * If we race with it entering cpu, unaccounted time is 0. This is + * indistinguishable from the read occurring a few cycles earlier. + */ + if (!p->on_cpu) + return p->se.sum_exec_runtime; +#endif + rq = task_rq_lock(p, &flags); ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq); task_rq_unlock(rq, p, &flags);
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