Commit-ID: fdccc3fb7a42ea4e4cd77d2fb8fa3a45c66ec0bf Gitweb: http://git.kernel.org/tip/fdccc3fb7a42ea4e4cd77d2fb8fa3a45c66ec0bf Author: leilei.lin <leilei....@alibaba-inc.com> AuthorDate: Wed, 9 Aug 2017 08:29:21 +0800 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Thu, 10 Aug 2017 12:08:40 +0200
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....@alibaba-inc.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: a...@kernel.org Cc: alexander.shish...@linux.intel.com Cc: eran...@gmail.com Cc: jo...@redhat.com Cc: linxiu...@gmail.com Cc: yang_oli...@hotmail.com Link: http://lkml.kernel.org/r/20170809002921.69813-1-leilei....@alibaba-inc.com [ Rewrote the changelog. ] Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/events/core.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/events/core.c b/kernel/events/core.c index ee20d4c..d704e23 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -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); }
