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

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Date:   Tue, 19 Dec 2017 15:10:04 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 12/19/2017 2:02 PM, Peter Zijlstra wrote:
> 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?
>

precise_ip will be checked before intel_pmu_pebs_read is called.
So @event must be a pebs event.

@@ -2060,6 +2060,14 @@ static void intel_pmu_del_event(struct perf_event 
*event)
  		intel_pmu_pebs_del(event);
  }

+static void intel_pmu_read_event(struct perf_event *event)
+{
+	if (event->attr.precise_ip)
+		return intel_pmu_pebs_read(event);
+
+	x86_perf_event_update(event, 0, 0);
+}