linux-kernel - Re: [PATCH v1 1/6] perf annotate: Delete session for debug builds

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Message-ID: <ZCVxXTc0kyRAQ+XA@kernel.org>
Date:   Thu, 30 Mar 2023 08:24:13 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Ian Rogers <irogers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, James Clark <james.clark@....com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        German Gomez <german.gomez@....com>,
        Sandipan Das <sandipan.das@....com>,
        Andres Freund <andres@...razel.de>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v1 1/6] perf annotate: Delete session for debug builds

Em Wed, Mar 29, 2023 at 05:13:17PM -0700, Namhyung Kim escreveu:
> On Wed, Mar 29, 2023 at 6:18 AM Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
> >
> > Em Wed, Mar 29, 2023 at 10:09:48AM -0300, Arnaldo Carvalho de Melo escreveu:
> > > Em Tue, Mar 28, 2023 at 04:55:38PM -0700, Ian Rogers escreveu:
> > > > Use the debug build indicator as the guide to free the session. This
> > > > implements a behavior described in a comment, which is consequentially
> > > > removed.
> > > >
> > > > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > > > ---
> > > >  tools/perf/builtin-annotate.c | 16 ++++++----------
> > > >  1 file changed, 6 insertions(+), 10 deletions(-)
> > > >
> > > > diff --git a/tools/perf/builtin-annotate.c b/tools/perf/builtin-annotate.c
> > > > index 4750fac7bf93..98d1b6379230 100644
> > > > --- a/tools/perf/builtin-annotate.c
> > > > +++ b/tools/perf/builtin-annotate.c
> > > > @@ -692,16 +692,12 @@ int cmd_annotate(int argc, const char **argv)
> > > >
> > > >  out_delete:
> > > >     /*
> > > > -    * Speed up the exit process, for large files this can
> > > > -    * take quite a while.
> > > > -    *
> > > > -    * XXX Enable this when using valgrind or if we ever
> > > > -    * librarize this command.
> > > > -    *
> > > > -    * Also experiment with obstacks to see how much speed
> > > > -    * up we'll get here.
> > > > -    *
> > > > -    * perf_session__delete(session);
> > > > +    * Speed up the exit process by only deleting for debug builds. For
> > > > +    * large files this can save time.
> > > >      */
> > > > +#ifndef NDEBUG
> > > > +   perf_session__delete(annotate.session);
> > > > +#endif
> > >
> > > So now, but default, we will call this, as we don't have this defined
> > > only if DEBUG=1 is set, right?
> > >
> > > ⬢[acme@...lbox perf-tools-next]$ find tools/perf/ -type f | xargs grep NDEBUG
> > > tools/perf/util/mutex.c:#ifndef NDEBUG
> > > ⬢[acme@...lbox perf-tools-next]$
> >
> > We can discuss this later, applied the series with just that zfree()
> > change to annotation_options__exit().
> 
> I don't think it's just an issue in the perf annotate.  Maybe we can
> do the same for perf report and so on.

Yes, I thought at some point of setting some flag, perf_exiting, and
then we would stop releasing memory, zfree comes to mind, but then we
would still be traversing data structures, taking locks, etc.

And we can't just exit() as we may need to flush caches, etc.

IIRC this specific case appeared in profiles, so was commented out.
 
> Anyway we could define NDEBUG=1 for release builds from now on.

Yes, we should do it.

- Arnaldo