sched: Optimize task_sched_runtime() (911b2898) · Commits · 戴 / test

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 −0

Original line number	Diff line number	Diff line
		@@ -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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