linux-kernel - Re: [PATCH] perf test: Remove atomics from test

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Date:   Sat, 25 Nov 2023 11:05:29 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Michael Petlan <mpetlan@...hat.com>
Cc:     Nick Forrington <nick.forrington@....com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        vmolnaro@...hat.com
Subject: Re: [PATCH] perf test: Remove atomics from test_loop to avoid test
 failures

Hi all,

On Fri, Nov 24, 2023 at 08:57:52PM +0100, Michael Petlan wrote:
> On Thu, 2 Nov 2023, Nick Forrington wrote:
> > The current use of atomics can lead to test failures, as tests (such as
> > tests/shell/record.sh) search for samples with "test_loop" as the
> > top-most stack frame, but find frames related to the atomic operation
> > (e.g. __aarch64_ldadd4_relax).

I am confused by above description.  As I went through the script
record.sh, which is the only test invoking the program 'test_loop',
but I don't find any test is related with stack frame.

Do I miss anything?  I went through record.sh but no clue why the
failure is caused by stack frame.  All the testings use command:

  if ! perf report -i "${perfdata}" -q | grep -q "${testsym}"
    ...
  fi

@Nick, could you narrow down which specific test case causing the
failure.

[...]

> I believe that it was there to prevent the compiler to optimize the loop
> out or some reason like that. Hopefully, it will work even without that
> on all architectures with all compilers that are used for building perf...

Agreed.

As said above, I'd like to step back a bit for making clear what's the
exactly failure caused by the program.

Thanks,
Leo