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

From: Ian Rogers
Date: Thu Oct 06 2022 - 14:52:25 EST


On Mon, Oct 3, 2022 at 1:46 PM Namhyung Kim <namhyung@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
> 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
>