linux-kernel - Re: [PATCH v7 0/6] perf record: Track sideband events for all CPUs when tracing selected CPUs

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Message-ID: <929ddd1f-dc15-079c-331d-13cc5f25a1a2@amd.com>
Date:   Tue, 29 Aug 2023 17:54:23 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Yang Jihong <yangjihong1@...wei.com>, acme@...nel.org,
        irogers@...gle.com, jolsa@...nel.org, namhyung@...nel.org,
        adrian.hunter@...el.com
Cc:     peterz@...radead.org, mingo@...hat.com, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, kan.liang@...ux.intel.com,
        james.clark@....com, tmricht@...ux.ibm.com, ak@...ux.intel.com,
        anshuman.khandual@....com, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH v7 0/6] perf record: Track sideband events for all CPUs
 when tracing selected CPUs

>> Number of actual samples are same ~38K. However, the perf.data file is 5x
>> bigger because of additional sideband data.
> 
> Yes, if record system wide sideband data, the amount of sideband events will increase proportionally, which is expected.
> 
>>
>> I'm pretty sure we don't need most of those additional data. So, thinking
>> loud, should we post-process perf.data file and filter out unnecessary data?
>>
> 
> I wonder if we can add a new function in perf inject.

Ok. perf inject is one option. But shall we do it bydefault in perf-record?
It's needed only when profiling target is set of cpus, not for systemwide or
per-process mode.

> By reading perf.data and comparing tid of SAMPLE events and sideband events, we can filter out the sideband data of unmatched tasks.

Yup. But AFAIK, perf-record keeps writing to perf.data and never does post-
processing on it. So adding support for this will take a bit of effort. Not
sure if we should do it as part of this series.

Thanks,
Ravi