linux-kernel - Re: [PATCH V3 13/23] perf evlist: Add evlist__add_dummy_on_all

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Date:   Wed, 11 May 2022 15:50:30 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ian Rogers <irogers@...gle.com>,
        Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>,
        Leo Yan <leo.yan@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 13/23] perf evlist: Add evlist__add_dummy_on_all_cpus()

On Wed, May 11, 2022 at 12:02 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> Add evlist__add_dummy_on_all_cpus() to enable creating a system-wide dummy
> event that sets up the system-wide maps before map propagation.
>
> For convenience, add evlist__add_aux_dummy() so that the logic can be used
> whether or not the event needs to be system-wide.
>
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
>
> Changes in V3: Amended comment about all CPUs.
>
>  tools/perf/util/evlist.c | 45 ++++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/evlist.h |  5 +++++
>  2 files changed, 50 insertions(+)
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 78c47cbafbc2..2b2900434bba 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -264,6 +264,51 @@ int evlist__add_dummy(struct evlist *evlist)
>         return 0;
>  }
>
> +static void evlist__add_on_all_cpus(struct evlist *evlist, struct evsel *evsel)
> +{
> +       evsel->core.system_wide = true;
> +
> +       /*
> +        * All CPUs.
> +        *
> +        * Note perf_event_open() does not accept CPUs that are not online, so
> +        * in fact this CPU list will include only all online CPUs.
> +        */
> +       perf_cpu_map__put(evsel->core.own_cpus);
> +       evsel->core.own_cpus = perf_cpu_map__new(NULL);
> +       perf_cpu_map__put(evsel->core.cpus);
> +       evsel->core.cpus = perf_cpu_map__get(evsel->core.own_cpus);

Maybe I'm missing something.. Wouldn't it be overwritten
by the user requested cpus during map propagation in
evlist__add()?

Thanks,
Namhyung


> +
> +       /* No threads */
> +       perf_thread_map__put(evsel->core.threads);
> +       evsel->core.threads = perf_thread_map__new_dummy();
> +
> +       evlist__add(evlist, evsel);
> +}
> +
> +struct evsel *evlist__add_aux_dummy(struct evlist *evlist, bool system_wide)
> +{
> +       struct evsel *evsel = evlist__dummy_event(evlist);
> +
> +       if (!evsel)
> +               return NULL;
> +
> +       evsel->core.attr.exclude_kernel = 1;
> +       evsel->core.attr.exclude_guest = 1;
> +       evsel->core.attr.exclude_hv = 1;
> +       evsel->core.attr.freq = 0;
> +       evsel->core.attr.sample_period = 1;
> +       evsel->no_aux_samples = true;
> +       evsel->name = strdup("dummy:u");
> +
> +       if (system_wide)
> +               evlist__add_on_all_cpus(evlist, evsel);
> +       else
> +               evlist__add(evlist, evsel);
> +
> +       return evsel;
> +}
> +
>  static int evlist__add_attrs(struct evlist *evlist, struct perf_event_attr *attrs, size_t nr_attrs)
>  {
>         struct evsel *evsel, *n;
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 4062f5aebfc1..1bde9ccf4e7d 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -114,6 +114,11 @@ int arch_evlist__add_default_attrs(struct evlist *evlist);
>  struct evsel *arch_evlist__leader(struct list_head *list);
>
>  int evlist__add_dummy(struct evlist *evlist);
> +struct evsel *evlist__add_aux_dummy(struct evlist *evlist, bool system_wide);
> +static inline struct evsel *evlist__add_dummy_on_all_cpus(struct evlist *evlist)
> +{
> +       return evlist__add_aux_dummy(evlist, true);
> +}
>
>  int evlist__add_sb_event(struct evlist *evlist, struct perf_event_attr *attr,
>                          evsel__sb_cb_t cb, void *data);
> --
> 2.25.1
>