linux-kernel - Re: [perf stat] Extend --cpu to non-system-wide runs too? was Re: [PATCH v3] perf bench sched pipe: Add -G/--cgroups option

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Message-ID: <CAM9d7cjLxtDPXXVWMG7SkPpsUrgh848texqH150XP+6+9ZqZxw@mail.gmail.com>
Date:   Tue, 17 Oct 2023 12:05:40 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [perf stat] Extend --cpu to non-system-wide runs too? was Re:
 [PATCH v3] perf bench sched pipe: Add -G/--cgroups option

On Tue, Oct 17, 2023 at 11:31 AM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> Em Tue, Oct 17, 2023 at 02:43:45PM +0200, Ingo Molnar escreveu:
> > * Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> > > Em Tue, Oct 17, 2023 at 01:40:07PM +0200, Ingo Molnar escreveu:
> > > > Side note: it might make sense to add a sane cpumask/affinity setting
> > > > option to perf stat itself:
>
> > > >   perf stat --cpumask
>
> > > > ... or so?
>
> > > > We do have -C:
>
> > > >     -C, --cpu <cpu>       list of cpus to monitor in system-wide
>
> > > > ... but that's limited to --all-cpus, right?
>
> > > > Perhaps we could extend --cpu to non-system-wide runs too?
>
> > > Maybe I misunderstood your question, but its a list of cpus to limit the
> > > counting:
>
> > Ok.
>
> > So I thought that "--cpumask mask/list/etc" should simply do what 'taskset'
> > is doing: using the sched_setaffinity() syscall to make the current
> > workload and all its children.
>
> > There's impact on perf stat itself: it could just call sched_setaffinity()
> > early on, and not bother about it?
>
> > Having it built-in into perf would simply make it easier to not forget
> > running 'taskset'. :-)
>
> Would that be the only advantage?
>
> I think using taskset isn't that much of a burden and keeps with the
> Unix tradition, no? :-\

Agreed.  Maybe there's a usecase that wants to profile a specific
cpu while the target processes are running all available cpus.

Thanks,
Namhyung