linux-kernel - Re: [PATCH 0/4] perf lock contention: Improve call stack handling (v1)

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Message-ID: <CAM9d7cgOPUoGr96yc=M=bBTQG-jkW269Lc7-uEYTWGURiCAjyQ@mail.gmail.com>
Date:   Thu, 8 Sep 2022 16:44:15 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        Song Liu <songliubraving@...com>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH 0/4] perf lock contention: Improve call stack handling (v1)

Hi Arnaldo,

On Thu, Sep 8, 2022 at 11:43 AM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> Em Wed, Sep 07, 2022 at 11:37:50PM -0700, Namhyung Kim escreveu:
> > Hello,
> >
> > I found that call stack from the lock tracepoint (using bpf_get_stackid)
> > can be different on each configuration.  For example it's very different
> > when I run it on a VM than on a real machine.
> >
> > The perf lock contention relies on the stack trace to get the lock
> > caller names, this kind of difference can be annoying.  Ideally we could
> > skip stack trace entries for internal BPF or lock functions and get the
> > correct caller, but it's not the case as of today.  Currently it's hard
> > coded to control the behavior of stack traces for the lock contention
> > tracepoints.
> >
> > To handle those differences, add two new options to control the number of
> > stack entries and how many it skips.  The default value worked well on
> > my VM setup, but I had to use --stack-skip=5 on real machines.
> >
> > You can get it from 'perf/lock-stack-v1' branch in
> >
> >   git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
>
> This clashed with a patch you Acked earlier, so lets see if someone has
> extra review comments and a v2 become needed for other reason, when you
> can refresh it, ok?

Sounds good!

Thanks,
Namhyung