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

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Date:   Thu, 8 Sep 2022 15:43:38 -0300
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@...r.kernel.org, Song Liu <songliubraving@...com>,
        bpf@...r.kernel.org
Subject: Re: [PATCH 0/4] perf lock contention: Improve call stack handling
 (v1)

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?

- Arnaldo
 
> Thanks,
> Namhyung
> 
> 
> Namhyung Kim (4):
>   perf lock contention: Factor out get_symbol_name_offset()
>   perf lock contention: Show full callstack with -v option
>   perf lock contention: Allow to change stack depth and skip
>   perf lock contention: Skip stack trace from BPF
> 
>  tools/perf/Documentation/perf-lock.txt        |  6 ++
>  tools/perf/builtin-lock.c                     | 89 ++++++++++++++-----
>  tools/perf/util/bpf_lock_contention.c         | 21 +++--
>  .../perf/util/bpf_skel/lock_contention.bpf.c  |  3 +-
>  tools/perf/util/lock-contention.h             |  3 +
>  5 files changed, 96 insertions(+), 26 deletions(-)
> 
> 
> base-commit: 6c3bd8d3e01d9014312caa52e4ef1c29d5249648
> -- 
> 2.37.2.789.g6183377224-goog

-- 

- Arnaldo