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

Jiri Olsa
2020-07-28T16:10:13Z

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

jirka

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