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

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Message-ID: <YFTEsOhbx4Il1nji@kernel.org>
Date:   Fri, 19 Mar 2021 12:35:12 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...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

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:

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

:-)

- Arnaldo