linux-kernel - Re: [PATCH 4/4] perf/x86/intel: drain PEBS buffer in event read

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Date:   Tue, 19 Dec 2017 20:02:14 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     mingo@...hat.com, acme@...nel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, jolsa@...hat.com, eranian@...gle.com,
        ak@...ux.intel.com
Subject: Re: [PATCH 4/4] perf/x86/intel: drain PEBS buffer in event read

On Mon, Dec 18, 2017 at 03:34:51AM -0800, kan.liang@...ux.intel.com wrote:
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -926,6 +926,16 @@ void intel_pmu_pebs_del(struct perf_event *event)
>  	pebs_update_state(needed_cb, cpuc, event->ctx->pmu);
>  }
>  
> +void intel_pmu_pebs_read(struct perf_event *event)
> +{
> +	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> +
> +	if (pebs_needs_sched_cb(cpuc))
> +		return intel_pmu_drain_pebs_buffer();
> +
> +	x86_perf_event_update(event, 0, 0);
> +}

This is completely broken.. what if @event isn't a pebs event, but we
do have an auto-reloading pebs event configured?