linux-kernel - Re: [PATCH 5/5] perf tools: Remove special handling of system-wide evsel

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Date:   Thu, 6 Oct 2022 11:57:31 -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 5/5] perf tools: Remove special handling of system-wide evsel

On Mon, Oct 3, 2022 at 1:46 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> For system-wide evsels, the thread map should be dummy - i.e. it has a
> single entry of -1.  But the code guarantees such a thread map, so no
> need to handle it specially.
>
> No functional change intended.
>
> Reviewed-by: Adrian Hunter <adrian.hunter@...el.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/lib/perf/evsel.c      |  3 ---
>  tools/perf/builtin-script.c |  3 ---
>  tools/perf/util/evsel.c     | 12 ++----------
>  tools/perf/util/stat.c      |  3 ---
>  4 files changed, 2 insertions(+), 19 deletions(-)
>
> diff --git a/tools/lib/perf/evsel.c b/tools/lib/perf/evsel.c
> index 8ce5bbd09666..8b51b008a81f 100644
> --- a/tools/lib/perf/evsel.c
> +++ b/tools/lib/perf/evsel.c
> @@ -515,9 +515,6 @@ int perf_evsel__alloc_id(struct perf_evsel *evsel, int ncpus, int nthreads)
>         if (ncpus == 0 || nthreads == 0)
>                 return 0;
>
> -       if (evsel->system_wide)
> -               nthreads = 1;
> -
>         evsel->sample_id = xyarray__new(ncpus, nthreads, sizeof(struct perf_sample_id));
>         if (evsel->sample_id == NULL)
>                 return -ENOMEM;
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> index 886f53cfa257..7fa467ed91dc 100644
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -2243,9 +2243,6 @@ static void __process_stat(struct evsel *counter, u64 tstamp)
>         struct perf_cpu cpu;
>         static int header_printed;
>
> -       if (counter->core.system_wide)
> -               nthreads = 1;
> -
>         if (!header_printed) {
>                 printf("%3s %8s %15s %15s %15s %15s %s\n",
>                        "CPU", "THREAD", "VAL", "ENA", "RUN", "TIME", "EVENT");
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 5776bfa70f11..e319bb17d10d 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1813,7 +1813,7 @@ static struct perf_thread_map *empty_thread_map;
>  static int __evsel__prepare_open(struct evsel *evsel, struct perf_cpu_map *cpus,
>                 struct perf_thread_map *threads)
>  {
> -       int nthreads;
> +       int nthreads = perf_thread_map__nr(threads);

A general nit for something not introduced by this change. nr/nthreads
here is really the number of perf_event_open file descriptors needed
for the thread map. I wonder if a variable name of num_thread_fds
would make the code more intention revealing.

Thanks,
Ian

>
>         if ((perf_missing_features.write_backward && evsel->core.attr.write_backward) ||
>             (perf_missing_features.aux_output     && evsel->core.attr.aux_output))
> @@ -1839,11 +1839,6 @@ static int __evsel__prepare_open(struct evsel *evsel, struct perf_cpu_map *cpus,
>                 threads = empty_thread_map;
>         }
>
> -       if (evsel->core.system_wide)
> -               nthreads = 1;
> -       else
> -               nthreads = threads->nr;
> -
>         if (evsel->core.fd == NULL &&
>             perf_evsel__alloc_fd(&evsel->core, perf_cpu_map__nr(cpus), nthreads) < 0)
>                 return -ENOMEM;
> @@ -2061,10 +2056,7 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
>         if (threads == NULL)
>                 threads = empty_thread_map;
>
> -       if (evsel->core.system_wide)
> -               nthreads = 1;
> -       else
> -               nthreads = threads->nr;
> +       nthreads = perf_thread_map__nr(threads);
>
>         if (evsel->cgrp)
>                 pid = evsel->cgrp->fd;
> diff --git a/tools/perf/util/stat.c b/tools/perf/util/stat.c
> index ce5e9e372fc4..cef943377ad7 100644
> --- a/tools/perf/util/stat.c
> +++ b/tools/perf/util/stat.c
> @@ -420,9 +420,6 @@ static int process_counter_maps(struct perf_stat_config *config,
>         int ncpus = evsel__nr_cpus(counter);
>         int idx, thread;
>
> -       if (counter->core.system_wide)
> -               nthreads = 1;
> -
>         for (thread = 0; thread < nthreads; thread++) {
>                 for (idx = 0; idx < ncpus; idx++) {
>                         if (process_counter_values(config, counter, idx, thread,
> --
> 2.38.0.rc1.362.ged0d419d3c-goog
>