linux-kernel - Re: [PATCH] perf/x86/intel: Drop kernel samples even though :u is specified

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Message-ID: <ae456a2e-a4c9-7cda-ab50-6135c53fe321@linux.intel.com>
Date:   Fri, 19 May 2017 20:24:19 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     acme@...nel.org, jolsa@...nel.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] perf/x86/intel: Drop kernel samples even though :u is
 specified



On 5/19/2017 8:10 PM, Peter Zijlstra wrote:
> On Fri, May 19, 2017 at 08:06:09PM +0800, Jin, Yao wrote:
>> SNIP
>>
>>> I would much rather see this in generic code, somewhere around
>>> __perf_event_overflow() I suppose. That would retain proper accounting
>>> for the interrupt rate etc..
>>>
>>> Also it would work for all architectures. Because I'm thinking more than
>>> just x86 will suffer from skid.
>> Yes, moving to generic code is better.  Thanks for the suggestion! I will do
>> that.
>>
>>> If you're really worried, I suppose you can put it behind a PERF_PMU_CAP
>>> flag or something.
>> I guess what you are suggesting is to add checking like:
>>
>> if (is_sampling_event(event)) {
>>      if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
>>          return;
>>      }
>> }
> Ah, I was more thinking of something like PERF_PMU_CAP_NO_SKID or
> something that would skip the test and preserve current behaviour.

OK, I understand now. For example, for PEBS event, its capabilities 
should be set with PERF_PMU_CAP_NO_SKID.

If the event's capabilities is set with PERF_PMU_CAP_NO_SKID, it should 
skip the checking and keep current behavior.

Thanks
Jin Yao