linux-kernel - Re: [PATCH 2/5] libperf: Propagate maps only if necessary

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Date:   Thu, 6 Oct 2022 11:52:05 -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 2/5] libperf: Propagate maps only if necessary

On Mon, Oct 3, 2022 at 1:46 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> The current code propagate evsel's cpu map settings to evlist when it's
> added to an evlist.  But the evlist->all_cpus and each evsel's cpus will
> be updated in perf_evlist__set_maps() later.  No need to do it before
> evlist's cpus are set actually.
>
> In fact it discards this intermediate all_cpus maps at the beginning
> of perf_evlist__set_maps().  Let's not do this.  It's only needed when
> an evsel is added after the evlist cpu/thread maps are set.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/lib/perf/evlist.c                  | 11 ++++-------
>  tools/lib/perf/include/internal/evlist.h |  1 +
>  2 files changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
> index 187129652ab6..8ce92070086c 100644
> --- a/tools/lib/perf/evlist.c
> +++ b/tools/lib/perf/evlist.c
> @@ -67,9 +67,7 @@ static void perf_evlist__propagate_maps(struct perf_evlist *evlist)
>  {
>         struct perf_evsel *evsel;
>
> -       /* Recomputing all_cpus, so start with a blank slate. */
> -       perf_cpu_map__put(evlist->all_cpus);
> -       evlist->all_cpus = NULL;
> +       evlist->needs_map_propagation = true;

Might be nice to also clear this in  perf_evlist__init.

>
>         perf_evlist__for_each_evsel(evlist, evsel)
>                 __perf_evlist__propagate_maps(evlist, evsel);
> @@ -81,7 +79,9 @@ void perf_evlist__add(struct perf_evlist *evlist,
>         evsel->idx = evlist->nr_entries;
>         list_add_tail(&evsel->node, &evlist->entries);
>         evlist->nr_entries += 1;
> -       __perf_evlist__propagate_maps(evlist, evsel);
> +
> +       if (evlist->needs_map_propagation)
> +               __perf_evlist__propagate_maps(evlist, evsel);

I think a comment here would be useful. Something like:
Adding events won't set the CPU maps in the evlist until
set_maps/propogate_maps is called. Catch the case that an evsel is
added after this and propagate the map.

Thanks,
Ian

>  }
>
>  void perf_evlist__remove(struct perf_evlist *evlist,
> @@ -177,9 +177,6 @@ void perf_evlist__set_maps(struct perf_evlist *evlist,
>                 evlist->threads = perf_thread_map__get(threads);
>         }
>
> -       if (!evlist->all_cpus && cpus)
> -               evlist->all_cpus = perf_cpu_map__get(cpus);
> -
>         perf_evlist__propagate_maps(evlist);
>  }
>
> diff --git a/tools/lib/perf/include/internal/evlist.h b/tools/lib/perf/include/internal/evlist.h
> index 6f89aec3e608..850f07070036 100644
> --- a/tools/lib/perf/include/internal/evlist.h
> +++ b/tools/lib/perf/include/internal/evlist.h
> @@ -19,6 +19,7 @@ struct perf_evlist {
>         int                      nr_entries;
>         int                      nr_groups;
>         bool                     has_user_cpus;
> +       bool                     needs_map_propagation;
>         /**
>          * The cpus passed from the command line or all online CPUs by
>          * default.
> --
> 2.38.0.rc1.362.ged0d419d3c-goog
>