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Re: [PATCH v3] perf/core: Avoid context switch overheads

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On Wed, Aug 09, 2017 at 08:29:21AM +0800, 石祤 wrote:
> From: "leilei.lin" <leilei.lin@alibaba-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@alibaba-inc.com>

Thanks!

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[PATCH v3] perf/core: Avoid context switch overheads "石祤" <linxiulei@gmail.com> - 2017-08-09 02:30 +0200
  Re: [PATCH v3] perf/core: Avoid context switch overheads Peter Zijlstra <peterz@infradead.org> - 2017-08-09 18:40 +0200
  [tip:perf/core] perf/core: Reduce context switch overhead "tip-bot for leilei.lin" <tipbot@zytor.com> - 2017-08-10 14:10 +0200

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