From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752441AbdHIAkg (ORCPT ); Tue, 8 Aug 2017 20:40:36 -0400 Received: from mail-oi0-f68.google.com ([209.85.218.68]:38478 "EHLO mail-oi0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752047AbdHIAke (ORCPT ); Tue, 8 Aug 2017 20:40:34 -0400 From: linxiulei To: yang_oliver@hotmail.com, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, eranian@gmail.com, torvalds@linux-foundation.org, jolsa@redhat.com, linxiulei@gmail.com Cc: "leilei . lin" Subject: [PATCH v3] perf/core: Avoid context switch overheads Date: Wed, 9 Aug 2017 08:40:19 +0800 Message-Id: <20170809004019.75458-1-linxiulei@gmail.com> X-Mailer: git-send-email 2.13.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "leilei.lin" 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. Therefore, 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 --- 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 (!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