linux-kernel - Re: [PATCH v3 5/9] perf build-id: Mark DSO in sample callchains

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Message-ID: <CAP-5=fV-cLLpdyoqL8+Jrt3iYU7EbpZZDOyM1kBCc+54gA2Nzg@mail.gmail.com>
Date: Wed, 28 May 2025 13:54:41 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: 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>, Kan Liang <kan.liang@...ux.intel.com>, 
	Athira Rajeev <atrajeev@...ux.ibm.com>, Kajol Jain <kjain@...ux.ibm.com>, 
	Li Huafei <lihuafei1@...wei.com>, "Steinar H. Gunderson" <sesse@...gle.com>, 
	James Clark <james.clark@...aro.org>, Stephen Brennan <stephen.s.brennan@...cle.com>, 
	Andi Kleen <ak@...ux.intel.com>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Zhongqiu Han <quic_zhonhan@...cinc.com>, Yicong Yang <yangyicong@...ilicon.com>, 
	Krzysztof Łopatowski <krzysztof.m.lopatowski@...il.com>, 
	"Dr. David Alan Gilbert" <linux@...blig.org>, Zixian Cai <fzczx123@...il.com>, 
	Steve Clevenger <scclevenger@...amperecomputing.com>, 
	Thomas Falcon <thomas.falcon@...el.com>, Martin Liska <martin.liska@....com>, 
	Martin Liška <m.liska@...link.cz>, 
	Song Liu <song@...nel.org>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/9] perf build-id: Mark DSO in sample callchains

On Wed, May 28, 2025 at 1:41 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Mon, Apr 28, 2025 at 02:34:04PM -0700, Ian Rogers wrote:
> > Previously only the sample IP's map DSO would be marked hit for the
> > purposes of populating the build ID cache. Walk the call chain to mark
> > all IPs and DSOs.
>
> I think this is correct, but I'm afraid it'd also increase the processing
> time.  Do you happen to have any numbers?

It increases time spent processing the data file but to get a large
data file I had to run for multiple seconds and I struggled to get the
performance cost of this to be in the milliseconds (ie a tiny fraction
of the record time). Ultimately I found the change imperceptible and
couldn't think of a good command line to make it perceptible.

If the time is spent populating ~/.debug because more DSOs are marked
then this is fixing a bug and isn't a problem with the patch.

My personal opinion is that it is somewhat surprising `perf record` is
post-processing the perf.data file at all, and -B and -N would be my
expected defaults - just as --buildid-mmap implies --no-buildid (-B).
I didn't want to modify existing behaviors in these changes, however,
in this case I was just trying to make the existing behavior correct,
similar to fixing the same bug in `perf inject`.

Thanks,
Ian

> Thanks,
> Namhyung
>
> >
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> >  tools/perf/util/build-id.c | 17 ++++++++++++++++-
> >  1 file changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
> > index aa35dceace90..3386fa8e1e7e 100644
> > --- a/tools/perf/util/build-id.c
> > +++ b/tools/perf/util/build-id.c
> > @@ -42,10 +42,20 @@
> >
> >  static bool no_buildid_cache;
> >
> > +static int mark_dso_hit_callback(struct callchain_cursor_node *node, void *data __maybe_unused)
> > +{
> > +     struct map *map = node->ms.map;
> > +
> > +     if (map)
> > +             dso__set_hit(map__dso(map));
> > +
> > +     return 0;
> > +}
> > +
> >  int build_id__mark_dso_hit(const struct perf_tool *tool __maybe_unused,
> >                          union perf_event *event,
> >                          struct perf_sample *sample,
> > -                        struct evsel *evsel __maybe_unused,
> > +                        struct evsel *evsel,
> >                          struct machine *machine)
> >  {
> >       struct addr_location al;
> > @@ -63,6 +73,11 @@ int build_id__mark_dso_hit(const struct perf_tool *tool __maybe_unused,
> >               dso__set_hit(map__dso(al.map));
> >
> >       addr_location__exit(&al);
> > +
> > +     sample__for_each_callchain_node(thread, evsel, sample, PERF_MAX_STACK_DEPTH,
> > +                                     /*symbols=*/false, mark_dso_hit_callback, /*data=*/NULL);
> > +
> > +
> >       thread__put(thread);
> >       return 0;
> >  }
> > --
> > 2.49.0.901.g37484f566f-goog
> >