Messages in this thread | | | Date | Tue, 8 Aug 2017 12:37:41 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2] perf/core: Avoid context switch overheads |
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On Tue, Aug 08, 2017 at 06:00:45PM +0800, 石祤 wrote:
> 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;
Do we really need the cpuctx->task_ctx test? I think that task_ctx is 'tight' these days. We never have it set unless there are events scheduled for that context.
I even think the cpuctx->task_ctx == ctx test right above here is superfluous these days. That could only happen when the perf_install_in_context() IPI came before perf_event_task_sched_in(), but we removed the arch option to do context switches with IRQs enabled.
> + > 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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