linux-kernel - Re: [PATCH v2 0/3] perf-stat: share hardware PMCs with BPF

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Message-ID: <CAM9d7cgoP28V_ONk2AJeu=Y7RQ8vzovzW=pGVYtERe97+ZH0Aw@mail.gmail.com>
Date:   Sat, 20 Mar 2021 00:58:10 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Song Liu <songliubraving@...com>, Jiri Olsa <jolsa@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v2 0/3] perf-stat: share hardware PMCs with BPF

Hi Arnaldo,

On Sat, Mar 20, 2021 at 12:35 AM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> Em Fri, Mar 19, 2021 at 09:54:59AM +0900, Namhyung Kim escreveu:
> > On Fri, Mar 19, 2021 at 9:22 AM Song Liu <songliubraving@...com> wrote:
> > > > On Mar 18, 2021, at 5:09 PM, Arnaldo <arnaldo.melo@...il.com> wrote:
> > > > On March 18, 2021 6:14:34 PM GMT-03:00, Jiri Olsa <jolsa@...hat.com> wrote:
> > > >> On Thu, Mar 18, 2021 at 03:52:51AM +0000, Song Liu wrote:
> > > >>> perf stat -C 1,3,5                  107.063 [sec]
> > > >>> perf stat -C 1,3,5 --bpf-counters   106.406 [sec]
>
> > > >> I can't see why it's actualy faster than normal perf ;-)
> > > >> would be worth to find out
>
> > > > Isn't this all about contended cases?
>
> > > Yeah, the normal perf is doing time multiplexing; while --bpf-counters
> > > doesn't need it.
>
> > Yep, so for uncontended cases, normal perf should be the same as the
> > baseline (faster than the bperf).  But for contended cases, the bperf
> > works faster.
>
> The difference should be small enough that for people that use this in a
> machine where contention happens most of the time, setting a
> ~/.perfconfig to use it by default should be advantageous, i.e. no need
> to use --bpf-counters on the command line all the time.
>
> So, Namhyung, can I take that as an Acked-by or a Reviewed-by? I'll take
> a look again now but I want to have this merged on perf/core so that I
> can work on a new BPF SKEL to use this:

I have a concern for the per cpu target, but it can be done later, so

Acked-by: Namhyung Kim <namhyung@...nel.org>

>
> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/log/?h=tmp.bpf/bpf_perf_enable

Interesting!  Actually I was thinking about the similar too. :)

Thanks,
Namhyung