linux-kernel - Re: [RFC/PATCHSET 00/19] perf stat: Cleanup counter aggregation (v1)

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Date:   Tue, 11 Oct 2022 20:58:40 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        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>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org,
        Kan Liang <kan.liang@...ux.intel.com>,
        Leo Yan <leo.yan@...aro.org>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        James Clark <james.clark@....com>,
        Xing Zhengjun <zhengjun.xing@...ux.intel.com>
Subject: Re: [RFC/PATCHSET 00/19] perf stat: Cleanup counter aggregation (v1)

On Tue, Oct 11, 2022 at 4:57 AM Andi Kleen <ak@...ux.intel.com> wrote:
>
>
> >> My main concern would be subtle regressions since there are so many
> >> different combinations and way to travel through the code, and a lot of
> >> things are not covered by unit tests. When I worked on the code it was
> >> difficult to keep it all working. I assume you have some way to
> >> enumerate them all and tested that the output is identical?
> > Right, that's my concern too.
> >
> > I have tested many combinations manually and checked if they
> > produced similar results.
>
> I had a script to test many combinations, but had to check the output
> manually
>
>
> > But the problem is that I cannot test
> > all hardwares and more importantly it's hard to check
> > programmatically if the output is the same or not.
>
> Can use "dummy" or some software event (e.g. a probe on some syscall) to
> get stable numbers. I don't think we need to cover all hardware for the
> output options, the different events should be similar, but need some
> coverage for the different aggregation. Or we could add some more tool
> events just for testing purposes, that would allow covering different
> core scopes etc. and would easily allow generating known counts.

Even if we can get a stable number, it still needs to know cpu topology
for different aggregation modes to verify the count.  Also I'm afraid that
cpu hotplug can affect the aggregation.

Thanks,
Namhyung