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

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Date:   Tue, 4 Oct 2022 08:20:58 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Namhyung Kim <namhyung@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.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 30/09/22 20:27, Namhyung Kim 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>

Reviewed-by: Adrian Hunter <adrian.hunter@...el.com>

> ---
>  tools/lib/perf/evlist.c                  | 8 ++++----
>  tools/lib/perf/include/internal/evlist.h | 1 +
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
> index 187129652ab6..c5f65b89d77a 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;
>  
>  	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);
>  }
>  
>  void perf_evlist__remove(struct perf_evlist *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.