Commit fdccc3fb authored Aug 09, 2017 by leilei.lin Committed by Ingo Molnar Aug 10, 2017

perf/core: Reduce context switch overhead



Skip most of the PMU context switching overhead when ctx->nr_events is 0.

50% performance overhead was observed under an extreme testcase.

Signed-off-by: leilei.lin <leilei.lin@alibaba-inc.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@kernel.org
Cc: alexander.shishkin@linux.intel.com
Cc: eranian@gmail.com
Cc: jolsa@redhat.com
Cc: linxiulei@gmail.com
Cc: yang_oliver@hotmail.com
Link: http://lkml.kernel.org/r/20170809002921.69813-1-leilei.lin@alibaba-inc.com


[ Rewrote the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent ab027620

kernel/events/core.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -3211,6 +3211,13 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
		return;

		perf_ctx_lock(cpuctx, ctx);
		/*
		* We must check ctx->nr_events while holding ctx->lock, such
		* that we serialize against perf_install_in_context().
		*/
		if (!ctx->nr_events)
		goto unlock;

		perf_pmu_disable(ctx->pmu);
		/*
		* We want to keep the following priority order:
		@@ -3224,6 +3231,8 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
		cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
		perf_event_sched_in(cpuctx, ctx, task);
		perf_pmu_enable(ctx->pmu);

		unlock:
		perf_ctx_unlock(cpuctx, ctx);
		}

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