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From: Ian Rogers <irogers@google.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	Athira Rajeev <atrajeev@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH v2 1/5] perf record: Set PERF_RECORD_PERIOD if attr->freq is set.
Date: Thu, 3 Sep 2020 22:39:01 -0700	[thread overview]
Message-ID: <CAP-5=fXbLtiX5Syji7X=-tV8r=PbbTw7X63h4PfggT-XvUemtQ@mail.gmail.com> (raw)
In-Reply-To: <CAP-5=fUJW+UkL-jZkzkCKqTLh7DC0XnFx06kdfYiu2CK85Wq1w@mail.gmail.com>

On Wed, Jul 29, 2020 at 2:43 PM Ian Rogers <irogers@google.com> wrote:
>
> On Wed, Jul 29, 2020 at 11:52 AM Arnaldo Carvalho de Melo
> <acme@kernel.org> wrote:
> >
> > Em Tue, Jul 28, 2020 at 01:57:30AM -0700, Ian Rogers escreveu:
> > > From: David Sharp <dhsharp@google.com>
> > >
> > > evsel__config() would only set PERF_RECORD_PERIOD if it set attr->freq
> >
> > There is no such thing as 'PERF_RECORD_PERIOD', its PERF_SAMPLE_PERIOD,
> > also...
> >
> > > from perf record options. When it is set by libpfm events, it would not
> > > get set. This changes evsel__config to see if attr->freq is set outside of
> > > whether or not it changes attr->freq itself.
> > >
> > > Signed-off-by: David Sharp <dhsharp@google.com>
> > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > ---
> > >  tools/perf/util/evsel.c | 7 ++++++-
> > >  1 file changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > > index ef802f6d40c1..811f538f7d77 100644
> > > --- a/tools/perf/util/evsel.c
> > > +++ b/tools/perf/util/evsel.c
> > > @@ -979,13 +979,18 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
> > >       if (!attr->sample_period || (opts->user_freq != UINT_MAX ||
> > >                                    opts->user_interval != ULLONG_MAX)) {
> > >               if (opts->freq) {
> > > -                     evsel__set_sample_bit(evsel, PERIOD);
> > >                       attr->freq              = 1;
> > >                       attr->sample_freq       = opts->freq;
> > >               } else {
> > >                       attr->sample_period = opts->default_interval;
> > >               }
> > >       }
> > > +     /*
> > > +      * If attr->freq was set (here or earlier), ask for period
> > > +      * to be sampled.
> > > +      */
> > > +     if (attr->freq)
> > > +             evsel__set_sample_bit(evsel, PERIOD);
> >
> > Why can't the libpfm code set opts?
> >
> > With this patch we will end up calling evsel__set_sample_bit(evsel,
> > PERIOD) twice, which isn't a problem but looks strange.
>
> Thanks Arnaldo! The case I was looking at was something like:
> perf record --pfm-events cycles:freq=1000
>
> For regular events this would be:
> perf record -e cycles/freq=1000/
>
> With libpfm4 events the perf_event_attr is set up (a public API in
> linux/perf_event.h) and then parse_events__add_event is used (an
> internal API) to make the evsel and this added to the evlist
> (parse_libpfm_events_option). This is similar to the parse_events
> function except rather than set up a perf_event_attr the regular
> parsing sets up config terms that are then applied to evsel and attr
> later in evsel__config, via evsel__apply_config_terms.
>
> I think we can  update this change so that in pfm.c after
> parse_events__add_event we do:
> if (attr.freq)
>   evsel__set_sample_bit(evsel, PERIOD);
>
> This code could also be part of parse_events__add_event. I think the
> intent in placing this code here was that it is close to the similar
> evsel__apply_config_terms and setting of sample bits in the evsel. The
> logic here is already dependent on reading the attr->sample_period.
>
> I'm not sure I follow the double setting case - I think that is only
> possible with a config term or with period_set (-P).
>
> Thanks,
> Ian

Polite ping. Thanks,
Ian

>
> > - Arnaldo
> >
> > >
> > >       if (opts->no_samples)
> > >               attr->sample_freq = 0;
> > > --
> > > 2.28.0.163.g6104cc2f0b6-goog
> > >
> >
> > --
> >
> > - Arnaldo

  reply	other threads:[~2020-09-04  5:39 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-28  8:57 [PATCH v2 0/5] Fixes for setting event freq/periods Ian Rogers
2020-07-28  8:57 ` [PATCH v2 1/5] perf record: Set PERF_RECORD_PERIOD if attr->freq is set Ian Rogers
2020-07-28 15:43   ` Jiri Olsa
2020-07-28 16:03     ` Arnaldo Carvalho de Melo
2020-07-29 15:11       ` Athira Rajeev
2020-07-29 18:52   ` Arnaldo Carvalho de Melo
2020-07-29 21:43     ` Ian Rogers
2020-09-04  5:39       ` Ian Rogers [this message]
2020-07-28  8:57 ` [PATCH v2 2/5] perf record: Prevent override of attr->sample_period for libpfm4 events Ian Rogers
2020-07-28 15:59   ` Jiri Olsa
2020-07-28 16:09     ` Jiri Olsa
2020-07-29 23:24       ` Ian Rogers
2020-09-04  5:41         ` Ian Rogers
2020-09-04 16:03           ` Jiri Olsa
2020-09-04 16:22             ` Ian Rogers
2020-09-04 18:48               ` Arnaldo Carvalho de Melo
2020-09-04 18:50                 ` Arnaldo Carvalho de Melo
2020-09-04 18:51                   ` Arnaldo Carvalho de Melo
2020-09-11 22:34                     ` Ian Rogers
2020-09-12  3:02                       ` Ian Rogers
2020-07-29 18:54   ` Arnaldo Carvalho de Melo
2020-07-28  8:57 ` [PATCH v2 3/5] perf test: Ensure sample_period is set " Ian Rogers
2020-07-28 12:45   ` Arnaldo Carvalho de Melo
2020-07-28  8:57 ` [PATCH v2 4/5] perf record: Don't clear event's period if set by a term Ian Rogers
2020-07-29 18:58   ` Arnaldo Carvalho de Melo
2020-08-04 10:08   ` Adrian Hunter
2020-08-04 13:33     ` Ian Rogers
2020-08-04 14:48       ` Adrian Hunter
2020-08-04 15:50         ` Ian Rogers
2020-09-04  5:43           ` Ian Rogers
2020-09-07  6:36             ` Adrian Hunter
2020-07-28  8:57 ` [PATCH v2 5/5] perf test: Leader sampling shouldn't clear sample period Ian Rogers

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