linux-kernel - Re: [RESEND PATCH V2 3/4] perf/x86/intel: drain PEBS buffer in event read

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Date:   Wed, 10 Jan 2018 09:31:56 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        eranian@...gle.com, ak@...ux.intel.com
Subject: Re: [RESEND PATCH V2 3/4] perf/x86/intel: drain PEBS buffer in event
 read



On 1/10/2018 5:39 AM, Jiri Olsa wrote:
> On Mon, Jan 08, 2018 at 07:15:15AM -0800, kan.liang@...el.com wrote:
>> From: Kan Liang <kan.liang@...ux.intel.com>
>>
>> When the PEBS interrupt threshold is larger than one, there is no way to
>> get exact auto-reload times and value needed for event update unless
>> flush the PEBS buffer.
>>
>> Drain the PEBS buffer in event read when large PEBS is enabled.
>>
>> For the threshold is one, even auto-reload is enabled, it doesn't need
>> to be specially handled. Because auto-reload is only effect when event
>> overflow. There is no overflow in event read.
>>
>> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
>> ---
>>   arch/x86/events/intel/core.c |  9 +++++++++
>>   arch/x86/events/intel/ds.c   | 10 ++++++++++
>>   arch/x86/events/perf_event.h |  2 ++
>>   3 files changed, 21 insertions(+)
>>
>> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
>> index 09c26a4..bdc35f8 100644
>> --- a/arch/x86/events/intel/core.c
>> +++ b/arch/x86/events/intel/core.c
>> @@ -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);
> 
> check for (event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD)
> would be more accurate?
> 

It will narrow down the events.
But considering the readability, I think it would be better to use 
precise_ip.The exposed functions in ds.c should be generic functions for 
all PEBS events, not specific case.
I think _AUTO_RELOAD looks too specific.

Thanks,
Kan