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Commit fdccc3fb authored by leilei.lin's avatar leilei.lin Committed by Ingo Molnar
Browse files

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: default avatarleilei.lin <leilei.lin@alibaba-inc.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent ab027620

kernel/events/core.c

+9 −0
Original line number Original line Diff line number Diff line
@@ -3211,6 +3211,13 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx, 
		return;

		return;





	perf_ctx_lock(cpuctx, ctx);

	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);

	perf_pmu_disable(ctx->pmu);

	/*

	/*

	 * We want to keep the following priority order:

	 * 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);

		cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);

	perf_event_sched_in(cpuctx, ctx, task);

	perf_event_sched_in(cpuctx, ctx, task);

	perf_pmu_enable(ctx->pmu);

	perf_pmu_enable(ctx->pmu);



unlock:

	perf_ctx_unlock(cpuctx, ctx);

	perf_ctx_unlock(cpuctx, ctx);

}

}