Re: [PATCH] perf tools: Move probing cgroup sampling support

[Namhyung Kim]

Hi Arnaldo,

On Tue, Jun 1, 2021 at 6:34 AM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
>
> Em Tue, Jun 01, 2021 at 10:30:25AM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Thu, May 27, 2021 at 11:28:35AM -0700, Namhyung Kim escreveu:
> > > I found that checking cgroup sampling support using the missing
> > > features doesn't work on old kernels.  Because it added both
> > > attr.cgroup bit and PERF_SAMPLE_CGROUP bit, it needs to check
> > > whichever comes first (usually the actual event, not dummy).
> > >
> > > But it only checks the attr.cgroup bit which is set only in the dummy
> > > event so cannot detect failtures due the sample bits.  Also we don't
> > > ignore the missing feature and retry, it'd be better checking it with
> > > the API probing logic.
> > >
> > > Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> > > ---
> > >  tools/perf/builtin-record.c      |  6 ++++++
> > >  tools/perf/util/evsel.c          |  6 +-----
> > >  tools/perf/util/evsel.h          |  1 -
> > >  tools/perf/util/perf_api_probe.c | 10 ++++++++++
> > >  tools/perf/util/perf_api_probe.h |  1 +
> > >  5 files changed, 18 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/tools/perf/util/perf_api_probe.c b/tools/perf/util/perf_api_probe.c
> > > index 829af17a0867..020411682a3c 100644
> > > --- a/tools/perf/util/perf_api_probe.c
> > > +++ b/tools/perf/util/perf_api_probe.c
> > > @@ -103,6 +103,11 @@ static void perf_probe_build_id(struct evsel *evsel)
> > >     evsel->core.attr.build_id = 1;
> > >  }
> > >
> > > +static void perf_probe_cgroup(struct evsel *evsel)
> > > +{
> > > +   evsel->core.attr.cgroup = 1;
> > > +}
> > > +
> > >  bool perf_can_sample_identifier(void)
> > >  {
> > >     return perf_probe_api(perf_probe_sample_identifier);
> > > @@ -182,3 +187,8 @@ bool perf_can_record_build_id(void)
> > >  {
> > >     return perf_probe_api(perf_probe_build_id);
> > >  }
> > > +
> > > +bool perf_can_record_cgroup(void)
> > > +{
> > > +   return perf_probe_api(perf_probe_cgroup);
> > > +}
> > > diff --git a/tools/perf/util/perf_api_probe.h b/tools/perf/util/perf_api_probe.h
> > > index f12ca55f509a..b104168efb15 100644
> > > --- a/tools/perf/util/perf_api_probe.h
> > > +++ b/tools/perf/util/perf_api_probe.h
> > > @@ -12,5 +12,6 @@ bool perf_can_record_switch_events(void);
> > >  bool perf_can_record_text_poke_events(void);
> > >  bool perf_can_sample_identifier(void);
> > >  bool perf_can_record_build_id(void);
> > > +bool perf_can_record_cgroup(void);
> > >
> > >  #endif // __PERF_API_PROBE_H
> > > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> > > index bc3dd379eb67..71efe6573ee7 100644
> > > --- a/tools/perf/builtin-record.c
> > > +++ b/tools/perf/builtin-record.c
> > > @@ -2733,6 +2733,12 @@ int cmd_record(int argc, const char **argv)
> > >             rec->no_buildid = true;
> > >     }
> > >
> > > +   if (rec->opts.record_cgroup && !perf_can_record_cgroup()) {
> > > +           pr_err("Kernel has no cgroup sampling support.\n");
> > > +           err = -EINVAL;
> > > +           goto out_opts;
> > > +   }
> > > +
> > >     if (rec->opts.kcore)
> > >             rec->data.is_dir = true;
> > >
> >
> > The above is perf/urgent material and should fix your issue, right?
> >
> > The part below is a separate patch and can be left for later, or maybe
> > remain in the codebase, as simple tools that use just one evsel and
> > request a cgroup will continue probing the kernel, etc. I.e. it
> > shouldn't get in the way for cases with dummies, etc.
> >
> > Simple tools then won't have to get that !perf_can_record_cgroup() call.
>
> I did it tentatively in my local branch, i.e. removed the removal of the
> fallback part, thus is just for it to be tested by the containers setup,
> etc, we can change this before it hits acme/perf/core externally.

Sure, thanks for doing this!

Thanks,
Namhyung