Re: [PATCH] perf stat: Ensure group is defined on top of the same cpu mask

[Ian Rogers]

On Sun, May 31, 2020 at 9:22 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Jin Yao reported the issue (and posted first versions of this change)
> with groups being defined over events with different cpu mask.
>
> This causes assert aborts in get_group_fd, like:
>
>   # perf stat -M "C2_Pkg_Residency" -a -- sleep 1
>   perf: util/evsel.c:1464: get_group_fd: Assertion `!(fd == -1)' failed.
>   Aborted
>
> All the events in the group have to be defined over the same
> cpus so the group_fd can be found for every leader/member pair.
>
> Adding check to ensure this condition is met and removing the
> group (with warning) if we detect mixed cpus, like:
>
>   $ sudo perf stat -e '{power/energy-cores/,cycles},{instructions,power/energy-cores/}'
>   WARNING: event cpu maps do not match, disabling group:
>     anon group { power/energy-cores/, cycles }
>     anon group { instructions, power/energy-cores/ }

This is really cool! I wonder if there is a better wording for 'event
cpu maps' ? It may be useful to list what the cpu maps are for the
events as a diagnostic aid.

Thanks,
Ian

> Fixes: 6a4bb04caacc8 ("perf tools: Enable grouping logic for parsed events")
> Co-developed-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
> Signed-off-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  tools/perf/builtin-stat.c | 51 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
>
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index b2b79aa161dd..512a41363d07 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -190,6 +190,55 @@ static struct perf_stat_config stat_config = {
>         .big_num                = true,
>  };
>
> +static bool cpus_map_matched(struct evsel *a, struct evsel *b)
> +{
> +       if (!a->core.cpus && !b->core.cpus)
> +               return true;
> +
> +       if (!a->core.cpus || !b->core.cpus)
> +               return false;
> +
> +       if (a->core.cpus->nr != b->core.cpus->nr)
> +               return false;
> +
> +       for (int i = 0; i < a->core.cpus->nr; i++) {
> +               if (a->core.cpus->map[i] != b->core.cpus->map[i])
> +                       return false;
> +       }
> +
> +       return true;
> +}
> +
> +static void evlist__check_cpu_maps(struct evlist *evlist)
> +{
> +       struct evsel *evsel, *pos, *leader;
> +       char buf[1024];
> +
> +       evlist__for_each_entry(evlist, evsel) {
> +               leader = evsel->leader;
> +
> +               /* Check that leader matches cpus with each member. */
> +               if (leader == evsel)
> +                       continue;
> +               if (cpus_map_matched(leader, evsel))
> +                       continue;
> +
> +               /*
> +                * If there's mismatch display dismantle the
> +                * group and warn user.
> +                */
> +               WARN_ONCE(1, "WARNING: group events cpu maps do not match, disabling group:\n");
> +               evsel__group_desc(leader, buf, sizeof(buf));
> +               pr_warning("  %s\n", buf);
> +
> +               for_each_group_evsel(pos, leader) {
> +                       pos->leader = pos;
> +                       pos->core.nr_members = 0;
> +               }
> +               evsel->leader->core.nr_members = 0;
> +       }
> +}
> +
>  static inline void diff_timespec(struct timespec *r, struct timespec *a,
>                                  struct timespec *b)
>  {
> @@ -1962,6 +2011,8 @@ int cmd_stat(int argc, const char **argv)
>         } else if (argc && !strncmp(argv[0], "rep", 3))
>                 return __cmd_report(argc, argv);
>
> +       evlist__check_cpu_maps(evsel_list);
> +
>         interval = stat_config.interval;
>         timeout = stat_config.timeout;
>
> --
> 2.25.4
>