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Date: Tue, 8 Aug 2017 18:00:45 +0800 From: "石祤" <linxiulei@...il.com> To: yang_oliver@...mail.com, peterz@...radead.org, mingo@...hat.com, acme@...nel.org, alexander.shishkin@...ux.intel.com, linux-kernel@...r.kernel.org, tglx@...utronix.de, eranian@...il.com, torvalds@...ux-foundation.org, jolsa@...hat.com, linxiulei@...il.com Cc: "leilei.lin" <leilei.lin@...baba-inc.com> Subject: [PATCH v2] perf/core: Avoid context switch overheads From: "leilei.lin" <leilei.lin@...baba-inc.com> A performance issue caused by less strickly check in task sched when these tasks were once attached by per-task perf_event. A task will alloc task->perf_event_ctxp[ctxn] when it was called by perf_event_open, and task->perf_event_ctxp[ctxn] would not ever be freed to NULL. __perf_event_task_sched_in() if (task->perf_event_ctxp[ctxn]) // here is always true perf_event_context_sched_in() // operate pmu 50% at most performance overhead was observed under some extreme test case. Therefor, add a more strick check as to ctx->nr_events, when ctx->nr_events == 0, it's no need to continue. Signed-off-by: leilei.lin <leilei.lin@...baba-inc.com> --- kernel/events/core.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/events/core.c b/kernel/events/core.c index 426c2ff..3d86695 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -3180,6 +3180,13 @@ 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 (!cpuctx->task_ctx && !ctx->nr_events) + goto unlock; + perf_pmu_disable(ctx->pmu); /* * We want to keep the following priority order: @@ -3193,6 +3200,8 @@ 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); } -- 2.8.4.31.g9ed660f
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