linux-kernel - Re: [PATCH 1/7] perf: cs-etm: Fix timeless decode mode detection

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Message-ID: <CADDJ8CWdKQR_-hgLqYdB6QyMZwzkZMtZ5gkoth3Uj7O7i3Cfvg@mail.gmail.com>
Date:   Tue, 25 Apr 2023 22:42:19 -0700
From:   Denis Nikitin <denik@...omium.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     James Clark <james.clark@....com>,
        linux-perf-users@...r.kernel.org, coresight@...ts.linaro.org,
        shy828301@...il.com, denik@...gle.com,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Leach <mike.leach@...aro.org>,
        John Garry <john.g.garry@...cle.com>,
        Will Deacon <will@...nel.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>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] perf: cs-etm: Fix timeless decode mode detection

On Mon, Apr 24, 2023 at 8:14 AM Suzuki K Poulose <suzuki.poulose@....com> wrote:
>
> On 24/04/2023 14:47, James Clark wrote:
> > In this context, timeless refers to the trace data rather than the perf
> > event data. But when detecting whether there are timestamps in the trace
> > data or not, the presence of a timestamp flag on any perf event is used.
> >
> > Since commit f42c0ce573df ("perf record: Always get text_poke events
> > with --kcore option") timestamps were added to a tracking event when
> > --kcore is used which breaks this detection mechanism. Fix it by
> > detecting if trace timestamps exist by looking at the ETM config flags.
> > This would have always been a more accurate way of doing it anyway.
> >
> > This fixes the following error message when using --kcore with
> > Coresight:
> >
> >    $ perf record --kcore -e cs_etm// --per-thread
> >    $ perf report
> >    The perf.data/data data has no samples!
> >
> > Fixes: f42c0ce573df ("perf record: Always get text_poke events with --kcore option")
> > Reported-by: Yang Shi <shy828301@...il.com>
> > Link: https://lore.kernel.org/lkml/CAHbLzkrJQTrYBtPkf=jf3OpQ-yBcJe7XkvQstX9j2frz4WF-SQ@mail.gmail.com/
> > Signed-off-by: James Clark <james.clark@....com>
> > ---
> >   tools/perf/util/cs-etm.c | 30 ++++++++++++++++++------------
> >   1 file changed, 18 insertions(+), 12 deletions(-)
> >
> > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> > index 8dd81ddd9e4e..50593289d53c 100644
> > --- a/tools/perf/util/cs-etm.c
> > +++ b/tools/perf/util/cs-etm.c
> > @@ -2684,26 +2684,29 @@ static int cs_etm__process_auxtrace_event(struct perf_session *session,
> >       return 0;
> >   }
> >
> > -static bool cs_etm__is_timeless_decoding(struct cs_etm_auxtrace *etm)
> > +static int cs_etm__setup_timeless_decoding(struct cs_etm_auxtrace *etm)
>
> minor nit: "setup" sound more like prepare to do what is required to
> do a timeless decoding, while we are doing more like, check if we
> have to do a timeless decoding. So may be:
>
> cs_etm_check_timeless_decoding() ?
>

I didn't catch that "setup_timeless_decoding" can be treated as the
initialization
of the timeless decoding. On the other hand _check_ doesn't imply that
it changes
the flag.
Maybe "_setup_timeless_decoding_flag" will be more specific about its intention?

- Denis

>
> Otherwise, looks good to me
>
> Suzuki
>
>
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