linux-kernel - Re: [RFC] perf arm-spe: Track task context switch for cpu-mode events

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Message-ID: <4ec2508a-d87a-ad91-87ec-dadef71bbc78@arm.com>
Date:   Wed, 6 Oct 2021 15:06:25 +0100
From:   James Clark <james.clark@....com>
To:     German Gomez <german.gomez@....com>, Leo Yan <leo.yan@...aro.org>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [RFC] perf arm-spe: Track task context switch for cpu-mode events



On 05/10/2021 11:06, German Gomez wrote:
> Hi Leo,
> 
> On 04/10/2021 07:26, Leo Yan wrote:
>> Hi James,
>>
>> On Thu, Sep 30, 2021 at 04:08:52PM +0100, James Clark wrote:
>>> On 23/09/2021 15:23, Leo Yan wrote:
>>>> On Thu, Sep 16, 2021 at 02:01:21PM -0700, Namhyung Kim wrote:
>> [...]
>> I'd like to use the comparison method for the test:
>> We should enable PID tracing and capture in the perf.data, when decode
>> the trace data, we can based on context packet and based on the switch
>> events to generate out two results, so we can check how the difference
>> between these results.
> 
> Yesterday we did some testing and found that there seems to be an exact
> match between using context packets and switch events. However this only
> applies when tracing in userspace (by adding the 'u' suffix to the perf
> event). Otherwise we still see as much as 2% of events having the wrong
> PID around the time of the switch.
> 
> In order to measure this I applied Namhyung's patch and James's patch
> from [1]. 

I thought that this had been applied already so I need to follow this up.

James

[...]
> 
> [1] https://www.spinics.net/lists/linux-perf-users/msg12543.html
>