linux-kernel - Re: [PATCH v1 5/5] perf record: Make --buildid-mmap the default

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Message-ID: <aAujYQH3yla8q3UQ@x1>
Date: Fri, 25 Apr 2025 11:59:45 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Namhyung Kim <namhyung@...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>,
	Stephen Brennan <stephen.s.brennan@...cle.com>,
	James Clark <james.clark@...aro.org>,
	Andi Kleen <ak@...ux.intel.com>, Dmitry Vyukov <dvyukov@...gle.com>,
	Zhongqiu Han <quic_zhonhan@...cinc.com>,
	Yicong Yang <yangyicong@...ilicon.com>,
	Michael Petlan <mpetlan@...hat.com>,
	Krzysztof Łopatowski <krzysztof.m.lopatowski@...il.com>,
	"Dr. David Alan Gilbert" <linux@...blig.org>,
	Leo Yan <leo.yan@....com>,
	Steve Clevenger <scclevenger@...amperecomputing.com>,
	Zixian Cai <fzczx123@...il.com>,
	Thomas Falcon <thomas.falcon@...el.com>,
	Martin Liska <martin.liska@....com>,
	Martin Liška <m.liska@...link.cz>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 5/5] perf record: Make --buildid-mmap the default

On Fri, Apr 25, 2025 at 11:45:28AM -0300, Arnaldo Carvalho de Melo wrote:
> On Thu, Apr 24, 2025 at 12:20:44AM -0700, Ian Rogers wrote:
> > On Wed, Apr 23, 2025 at 11:19 PM Ian Rogers <irogers@...gle.com> wrote:
> > > @@ -1795,7 +1796,8 @@ record__finish_output(struct record *rec)
> > >                         data->dir.files[i].size = lseek(data->dir.files[i].fd, 0, SEEK_CUR);
> > >         }
> > >
> > > -       if (!rec->no_buildid) {
> > > +       /* Buildid scanning disabled or build ID in kernel and synthesized map events. */
> > > +       if (!rec->no_buildid && !rec->buildid_mmap) {
>  
> > So I think this is wrong. It matches current behaviors, but it is
> > wrong. If we don't process the kernel's mmap events the DSOs won't be
> > loaded and the build ID cache won't contain the DSOs. There is also
> > the bug that the sample processing to find maps to find DSOs, doesn't
> > handle call chains. Given the broken nature of the build ID cache I'm
> > not sure it makes any sense for perf record to be by default
> > populating it. I think it probably makes sense to consider the default
> > population a legacy feature and make -N the default along with
> > --buildid-mmap.
> 
> The first four patches are good fixes/cleanups, so I'm picking them, ok?

I (and b4) missed v2, looking at it now.

- Arnaldo