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

From: Jiri Olsa <[email-masked]>
Date: Tue, 28 Jul 2020 18:09:54 +0200

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 <[email-masked]>
> > 
> > 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 <[email-masked]>
> > Reviewed-by: Ian Rogers <[email-masked]>
> > ---
> >  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 <[email-masked]>
> 
> thanks,
> jirka