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

[Namhyung Kim <namhyung@kernel.org>]

On Tue, Oct 17, 2023 at 11:31 AM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Em Tue, Oct 17, 2023 at 02:43:45PM +0200, Ingo Molnar escreveu:
> > * Arnaldo Carvalho de Melo <acme@kernel.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