linux-kernel - Re: [PATCH v2 5/7] perf, x86: drain PEBS buffer during context switch

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Date:	Tue, 15 Jul 2014 13:57:17 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, acme@...radead.org,
	eranian@...gle.com, andi@...stfloor.org
Subject: Re: [PATCH v2 5/7] perf, x86: drain PEBS buffer during context switch

On Tue, Jul 15, 2014 at 04:58:57PM +0800, Yan, Zheng wrote:
> +void intel_pmu_drain_pebs_buffer(void)
> +{
> +	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
> +	struct debug_store *ds = cpuc->ds;
> +	struct pt_regs regs;
> +
> +	if (!x86_pmu.pebs_active)
> +		return;
> +	if (ds->pebs_index <= ds->pebs_buffer_base)
> +		return;

Both implementations of drain_pebs() already do that.

> +	x86_pmu.drain_pebs(&regs);
> +}

> @@ -759,8 +787,19 @@ void intel_pmu_pebs_disable(struct perf_event *event)
>  {
>  	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
>  	struct hw_perf_event *hwc = &event->hw;
> +	struct debug_store *ds = cpuc->ds;
> +	bool multi_pebs = false;
> +
> +	if (ds->pebs_interrupt_threshold >
> +	    ds->pebs_buffer_base + x86_pmu.pebs_record_size)
> +		multi_pebs = true;
>  
>  	cpuc->pebs_enabled &= ~(1ULL << hwc->idx);
> +	if (cpuc->pebs_sched_cb_enabled &&
> +	    !(cpuc->pebs_enabled & ((1ULL << MAX_PEBS_EVENTS) - 1))) {

You seem fond of that expression, maybe make it an inline somewhere to
avoid all this repetition.

> +		perf_sched_cb_disable(event->ctx->pmu);
> +		cpuc->pebs_sched_cb_enabled = false;
> +	}
>  
>  	if (event->hw.constraint->flags & PERF_X86_EVENT_PEBS_LDLAT)
>  		cpuc->pebs_enabled &= ~(1ULL << (hwc->idx + 32));
> @@ -772,6 +811,9 @@ void intel_pmu_pebs_disable(struct perf_event *event)
>  
>  	hwc->config |= ARCH_PERFMON_EVENTSEL_INT;
>  	hwc->autoreload = false;
> +
> +	if (multi_pebs)
> +		intel_pmu_drain_pebs_buffer();
>  }

Is that condition worth the effort? Seeing how you already need to load
the DS state to compute multi_pebs in the first place.

> diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> index 430f1ad..a3df61d 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> @@ -199,8 +199,6 @@ void intel_pmu_lbr_enable(struct perf_event *event)
>  {
>  	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
>  
> -	if (!x86_pmu.lbr_nr)
> -		return;
>  	/*
>  	 * Reset the LBR stack if we changed task context to
>  	 * avoid data leaks.

More random hunks?

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