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

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Message-ID: <YysbKwpO9XLfHM90@kernel.org>
Date:   Wed, 21 Sep 2022 15:09:47 +0100
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...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)

Em Tue, Sep 20, 2022 at 02:04:47PM -0700, Namhyung Kim escreveu:
> On Tue, Sep 20, 2022 at 1:22 PM Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
> >
> > Em Thu, Sep 08, 2022 at 04:44:15PM -0700, Namhyung Kim escreveu:
> > > 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!
> >
> > Have you resubmitted this? /me goes on the backlog...
> 
> Yep :)
> 
> https://lore.kernel.org/r/20220912055314.744552-1-namhyung@kernel.org

It applies now, testing :-)

- Arnaldo