linux-kernel - Re: [PATCH 3/3] perf tests: Skip "test data symbol" on Neoverse N1

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Date: Tue, 9 Apr 2024 16:17:28 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: James Clark <james.clark@....com>, linux-perf-users@...r.kernel.org, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, "Liang, Kan" <kan.liang@...ux.intel.com>, 
	Athira Rajeev <atrajeev@...ux.vnet.ibm.com>, Leo Yan <leo.yan@...ux.dev>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] perf tests: Skip "test data symbol" on Neoverse N1

Hi Ian and James,

On Tue, Apr 9, 2024 at 8:39 AM Ian Rogers <irogers@...gle.com> wrote:
>
> On Tue, Apr 9, 2024 at 1:48 AM James Clark <james.clark@....com> wrote:
> >
> > To prevent anyone from seeing a test failure appear as a regression and
> > thinking that it was caused by their code change, just skip the test on
> > N1.
> >
> > It can be caused by any unrelated change that shifts the loop into an
> > unfortunate position in the Perf binary which is almost impossible to
> > debug as the root cause of the test failure. Ultimately it's caused by
> > the referenced errata.
> >
> > Fixes: 60abedb8aa90 ("perf test: Introduce script for data symbol testing")
> > Signed-off-by: James Clark <james.clark@....com>
>
> This change makes me sad :-( Is there no hope of aligning the loop? We
> have little enough testing coverage for memory events and even precise
> events on ARM that anything take away testing coverage feels like we
> should try to do better.

Can we just add some noise in the loop?

Thanks,
Namhyung


diff --git a/tools/perf/tests/workloads/datasym.c
b/tools/perf/tests/workloads/datasym.c
index ddd40bc63448..e2514bf393cd 100644
--- a/tools/perf/tests/workloads/datasym.c
+++ b/tools/perf/tests/workloads/datasym.c
@@ -16,6 +16,8 @@ static int datasym(int argc __maybe_unused, const
char **argv __maybe_unused)
 {
        for (;;) {
                buf1.data1++;
+               if ((buf1.data1 % 100129) == 0)
+                       buf1.data1++;
                buf1.data2 += buf1.data1;
        }
        return 0;