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Date: Wed, 9 Aug 2017 18:37:22 +0200 From: Peter Zijlstra <peterz@...radead.org> To: 石祤 <linxiulei@...il.com> Cc: yang_oliver@...mail.com, 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, "leilei.lin" <leilei.lin@...baba-inc.com> Subject: Re: [PATCH v3] perf/core: Avoid context switch overheads On Wed, Aug 09, 2017 at 08:29:21AM +0800, 石祤 wrote: > 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. 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 <leilei.lin@...baba-inc.com> Thanks!
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