linux-kernel - Re: [PATCH RFC 18/21] libperf evlist: Allow mixing per-thread and per-cpu mmaps

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Date:   Tue, 3 May 2022 13:29:20 -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 RFC 18/21] libperf evlist: Allow mixing per-thread and
 per-cpu mmaps

On Fri, Apr 22, 2022 at 9:25 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> mmap_per_evsel() will skip events that do not match the CPU, so all CPUs
> can be iterated in any case.
>
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
[...]
> @@ -561,9 +538,12 @@ static int perf_evlist__nr_mmaps(struct perf_evlist *evlist)
>  {
>         int nr_mmaps;
>
> +       /* One for each CPU */
>         nr_mmaps = perf_cpu_map__nr(evlist->all_cpus);
> -       if (perf_cpu_map__empty(evlist->all_cpus))
> -               nr_mmaps = perf_thread_map__nr(evlist->threads);
> +       /* One for each thread */
> +       nr_mmaps += perf_thread_map__nr(evlist->threads);
> +       /* Minus the dummy CPU or dummy thread */
> +       nr_mmaps -= 1;

I'm not sure it'd work for per-task events with default-per-cpu mode.

Thanks,
Namhyung

>
>         return nr_mmaps;
>  }