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

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Message-ID: <20200728160954.GD1319041@krava>
Date:   Tue, 28 Jul 2020 18:09:54 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ian Rogers <irogers@...gle.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>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        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 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

jirka

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