Re: [PATCH v2 2/5] perf record: Prevent override of attr->sample_period for libpfm4 events

From: Ian Rogers <irogers@google.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	Athira Rajeev <atrajeev@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH v2 2/5] perf record: Prevent override of attr->sample_period for libpfm4 events
Date: Wed, 29 Jul 2020 16:24:28 -0700	[thread overview]
Message-ID: <CAP-5=fVqto0LrwgW6dHQupp7jFA3wToRBonBaXXQW4wwYcTreg@mail.gmail.com> (raw)
In-Reply-To: <20200728160954.GD1319041@krava>

On Tue, Jul 28, 2020 at 9:10 AM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Tue, Jul 28, 2020 at 05:59:46PM +0200, Jiri Olsa wrote:
> > On Tue, Jul 28, 2020 at 01:57:31AM -0700, Ian Rogers wrote:
> > > From: Stephane Eranian <eranian@google.com>
> > >
> > > Before:
> > > $ perf record -c 10000 --pfm-events=cycles:period=77777
> > >
> > > Would yield a cycles event with period=10000, instead of 77777.
> > >
> > > This was due to an ordering issue between libpfm4 parsing
> > > the event string and perf record initializing the event.
> > >
> > > This patch fixes the problem by preventing override for
> > > events with attr->sample_period != 0 by the time
> > > perf_evsel__config() is invoked. This seems to have been the
> > > intent of the author.
> > >
> > > Signed-off-by: Stephane Eranian <eranian@google.com>
> > > Reviewed-by: Ian Rogers <irogers@google.com>
> > > ---
> > >  tools/perf/util/evsel.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > >
> > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > > index 811f538f7d77..8afc24e2ec52 100644
> > > --- a/tools/perf/util/evsel.c
> > > +++ b/tools/perf/util/evsel.c
> > > @@ -976,8 +976,7 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
> > >      * We default some events to have a default interval. But keep
> > >      * it a weak assumption overridable by the user.
> > >      */
> > > -   if (!attr->sample_period || (opts->user_freq != UINT_MAX ||
> > > -                                opts->user_interval != ULLONG_MAX)) {
> > > +   if (!attr->sample_period) {
> >
> > I was wondering why this wouldn't break record/top
> > but we take care of the via record_opts__config
> >
> > as long as 'perf test attr' works it looks ok to me
>
> hum ;-)
>
> [jolsa@krava perf]$ sudo ./perf test 17 -v
> 17: Setup struct perf_event_attr                          :
> ...
> running './tests/attr/test-record-C0'
> expected sample_period=4000, got 3000
> FAILED './tests/attr/test-record-C0' - match failure

I'm not able to reproduce this. Do you have a build configuration or
something else to look at? The test doesn't seem obviously connected
with this patch.

Thanks,
Ian

> jirka
>
> >
> > Acked-by: Jiri Olsa <jolsa@redhat.com>
> >
> > thanks,
> > jirka
>