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

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Date:   Fri, 6 May 2022 13:51:44 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Adrian Hunter <adrian.hunter@...el.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 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?

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
>