linux-kernel - Re: [PATCH 1/5] libperf: Populate system-wide evsel maps

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Date:   Thu, 6 Oct 2022 11:43:49 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org,
        Kan Liang <kan.liang@...ux.intel.com>,
        Leo Yan <leo.yan@...aro.org>
Subject: Re: [PATCH 1/5] libperf: Populate system-wide evsel maps

On Mon, Oct 3, 2022 at 1:46 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Setting proper cpu and thread maps for system wide evsels regardless of
> user requested cpu in __perf_evlist__propagate_maps().  Those evsels
> need to be active on all cpus always.  Do it in the libperf so that we
> can guarantee it has proper maps.
>
> Reviewed-by: Adrian Hunter <adrian.hunter@...el.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/lib/perf/evlist.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
> index 6b1bafe267a4..187129652ab6 100644
> --- a/tools/lib/perf/evlist.c
> +++ b/tools/lib/perf/evlist.c
> @@ -40,11 +40,11 @@ static void __perf_evlist__propagate_maps(struct perf_evlist *evlist,
>          * We already have cpus for evsel (via PMU sysfs) so
>          * keep it, if there's no target cpu list defined.
>          */

This comment is for the 'else if' case and so is a little out of place
before the system wide test.

> -       if (!evsel->own_cpus ||
> -           (!evsel->system_wide && evlist->has_user_cpus) ||
> -           (!evsel->system_wide &&
> -            !evsel->requires_cpu &&
> -            perf_cpu_map__empty(evlist->user_requested_cpus))) {
> +       if (evsel->system_wide) {
> +               perf_cpu_map__put(evsel->cpus);
> +               evsel->cpus = perf_cpu_map__new(NULL);

Looking at perf_cpu_map__new, will this mean that in system wide mode
every event/evsel will now read /sys/devices/system/cpu/online here?
We may want to cache the cpumap to avoid this.

Thanks,
Ian

> +       } else if (!evsel->own_cpus || evlist->has_user_cpus ||
> +                  (!evsel->requires_cpu && perf_cpu_map__empty(evlist->user_requested_cpus))) {
>                 perf_cpu_map__put(evsel->cpus);
>                 evsel->cpus = perf_cpu_map__get(evlist->user_requested_cpus);
>         } else if (evsel->cpus != evsel->own_cpus) {
> @@ -52,7 +52,10 @@ static void __perf_evlist__propagate_maps(struct perf_evlist *evlist,
>                 evsel->cpus = perf_cpu_map__get(evsel->own_cpus);
>         }
>
> -       if (!evsel->system_wide) {
> +       if (evsel->system_wide) {
> +               perf_thread_map__put(evsel->threads);
> +               evsel->threads = perf_thread_map__new_dummy();
> +       } else {
>                 perf_thread_map__put(evsel->threads);
>                 evsel->threads = perf_thread_map__get(evlist->threads);
>         }
> --
> 2.38.0.rc1.362.ged0d419d3c-goog
>