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Commit 911b2898 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarLarry Woodman <lwoodman@redhat.com>
Suggested-by: default avatarPaul Turner <pjt@google.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent 5eca82a9

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);