linux-kernel - Re: [PATCH V2 21/23] libperf evsel: Add comments for booleans

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Message-ID: <ec62edc2-f4fc-82db-c001-23d43137557c@intel.com>
Date:   Wed, 11 May 2022 10:03:13 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Leo Yan <leo.yan@...aro.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 21/23] libperf evsel: Add comments for booleans

On 6/05/22 23:51, Ian Rogers wrote:
> On Fri, May 6, 2022 at 5:26 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>
>> Add comments for 'system_wide' and 'requires_cpu' booleans
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>> ---
>>  tools/lib/perf/include/internal/evsel.h | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/tools/lib/perf/include/internal/evsel.h b/tools/lib/perf/include/internal/evsel.h
>> index 77fbb8b97e5c..cc8f1ba790bd 100644
>> --- a/tools/lib/perf/include/internal/evsel.h
>> +++ b/tools/lib/perf/include/internal/evsel.h
>> @@ -49,7 +49,16 @@ struct perf_evsel {
>>
>>         /* parse modifier helper */
>>         int                      nr_members;
>> +       /*
>> +        * system_wide is for events that need to be on every CPU, irrespective
>> +        * of user requested CPUs or threads. Map propagation will not override
>> +        * this events own_cpus, which will contribute to evlist all_cpus.
> 
> So this muddies my understanding of cpus and own_cpus (sigh, again
> undocumented). I believe cpus to be the set of CPUs (or any CPU, aka
> dummy) that perf_event_open happens on. all_cpus in evlist is the
> union of all the evsels cpus (ie not related to own_cpus as described
> here). Own_cpus I believe to be what's computed at parse-event time
> from sysfs. Is this a typo in the comment or quite likely my error?

A 'system_wide' event is not created by the parser, so own_cpus is set
by the code adding the event.

> 
> Thanks,
> Ian
> 
>> +        */
>>         bool                     system_wide;
>> +       /*
>> +        * Some events, for example uncore events, require a CPU.
>> +        * i.e. it cannot be the 'any CPU' value of -1.
>> +        */
>>         bool                     requires_cpu;
>>         int                      idx;
>>  };
>> --
>> 2.25.1
>>