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

Ian Rogers
2020-09-04T16:22:30Z

On Fri, Sep 4, 2020 at 9:03 AM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Thu, Sep 03, 2020 at 10:41:14PM -0700, Ian Rogers wrote:
> > On Wed, Jul 29, 2020 at 4:24 PM Ian Rogers <irogers@google.com> wrote:
> > >
> > > 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
> >
> > Jiri, any update? Thanks,
>
> sorry, I rebased and ran it again and it passes for me now,
> so it got fixed along the way

No worries, thanks for the update! It'd be nice to land this and the
other libpfm fixes.

Ian

> jirka
>