netdev - Re: [PATCH v2 2/5] perf record: Prevent override of attr->sample

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Date:   Wed, 29 Jul 2020 16:24:28 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
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>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 2/5] perf record: Prevent override of
 attr->sample_period for libpfm4 events

On Tue, Jul 28, 2020 at 9:10 AM Jiri Olsa <jolsa@...hat.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@...gle.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@...gle.com>
> > > Reviewed-by: Ian Rogers <irogers@...gle.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@...va 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@...hat.com>
> >
> > thanks,
> > jirka
>