Re: [PATCH V2 2/4] perf stat: Always keep perf metrics topdown events in a group

Ian Rogers
2022-05-17T03:11:32Z

On Mon, May 16, 2022 at 8:25 AM <kan.liang@linux.intel.com> wrote:
>
> From: Kan Liang <kan.liang@linux.intel.com>
>
> If any member in a group has a different cpu mask than the other
> members, the current perf stat disables group. when the perf metrics
> topdown events are part of the group, the below <not supported> error
> will be triggered.
>
> $ perf stat -e "{slots,topdown-retiring,uncore_imc_free_running_0/dclk/}" -a sleep 1
> WARNING: grouped events cpus do not match, disabling group:
> anon group { slots, topdown-retiring, uncore_imc_free_running_0/dclk/ }
>
> Performance counter stats for 'system wide':
>
> 141,465,174 slots
> <not supported> topdown-retiring
> 1,605,330,334 uncore_imc_free_running_0/dclk/
>
> The perf metrics topdown events must always be grouped with a slots
> event as leader.
>
> Factor out evsel__remove_from_group() to only remove the regular events
> from the group.
>
> Remove evsel__must_be_in_group(), since no one use it anymore.
>
> With the patch, the topdown events aren't broken from the group for the
> splitting.
>
> $ perf stat -e "{slots,topdown-retiring,uncore_imc_free_running_0/dclk/}" -a sleep 1
> WARNING: grouped events cpus do not match, disabling group:
> anon group { slots, topdown-retiring, uncore_imc_free_running_0/dclk/ }
>
> Performance counter stats for 'system wide':
>
> 346,110,588 slots
> 124,608,256 topdown-retiring
> 1,606,869,976 uncore_imc_free_running_0/dclk/
>
> 1.003877592 seconds time elapsed
>
> Fixes: a9a1790247bd ("perf stat: Ensure group is defined on top of the same cpu mask")
> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
> ---
> tools/perf/builtin-stat.c | 7 +++----
> tools/perf/util/evlist.c | 6 +-----
> tools/perf/util/evsel.c | 13 +++++++++++--
> tools/perf/util/evsel.h | 2 +-
> 4 files changed, 16 insertions(+), 12 deletions(-)
>
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index a96f106dc93a..75c88c7939b1 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -271,10 +271,9 @@ static void evlist__check_cpu_maps(struct evlist *evlist)
> pr_warning(" %s: %s\n", evsel->name, buf);
> }
>
> - for_each_group_evsel(pos, leader) {
> - evsel__set_leader(pos, pos);
> - pos->core.nr_members = 0;
> - }
> + for_each_group_evsel(pos, leader)
> + evsel__remove_from_group(pos, leader);
> +
> evsel->core.leader->nr_members = 0;

This shouldn't be necessary now.

> }
> }
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index dfa65a383502..7fc544330fea 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -1795,11 +1795,7 @@ struct evsel *evlist__reset_weak_group(struct evlist *evsel_list, struct evsel *
> * them. Some events, like Intel topdown, require being
> * in a group and so keep these in the group.
> */
> - if (!evsel__must_be_in_group(c2) && c2 != leader) {
> - evsel__set_leader(c2, c2);
> - c2->core.nr_members = 0;
> - leader->core.nr_members--;
> - }
> + evsel__remove_from_group(c2, leader);
>
> /*
> * Set this for all former members of the group
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index b98882cbb286..deb428ee5e50 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -3083,7 +3083,16 @@ bool __weak arch_evsel__must_be_in_group(const struct evsel *evsel __maybe_unuse
> return false;
> }
>
> -bool evsel__must_be_in_group(const struct evsel *evsel)
> +/*
> + * Remove an event from a given group (leader).
> + * Some events, e.g., perf metrics Topdown events,
> + * must always be grouped. Ignore the events.
> + */
> +void evsel__remove_from_group(struct evsel *evsel, struct evsel *leader)
> {
> - return arch_evsel__must_be_in_group(evsel);
> + if (!arch_evsel__must_be_in_group(evsel) && evsel != leader) {
> + evsel__set_leader(evsel, evsel);
> + evsel->core.nr_members = 0;
> + leader->core.nr_members--;
> + }

Should we also have:

if (leader->core.nr_members == 1)
leader->core.nr_members = 0;

Other wise say:

{instructions,cycles}

with a remove of cycles becomes:

{instructions}, cycles

rather than the previous:

instructions,cycles

Actually, looking at:
https://lore.kernel.org/lkml/20220512061308.1152233-2-irogers@google.com/

+ /* Reset the leader count if all entries were removed. */
+ if (leader->core.nr_members)
+ leader->core.nr_members = 0;

is wrong and should be:

+ /* Reset the leader count if all entries were removed. */
+ if (leader->core.nr_members == 1)
+ leader->core.nr_members = 0;

I'll fix and re-send.

Thanks,
Ian

> }
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index a36172ed4cf6..47f65f8e7c74 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -483,7 +483,7 @@ bool evsel__has_leader(struct evsel *evsel, struct evsel *leader);
> bool evsel__is_leader(struct evsel *evsel);
> void evsel__set_leader(struct evsel *evsel, struct evsel *leader);
> int evsel__source_count(const struct evsel *evsel);
> -bool evsel__must_be_in_group(const struct evsel *evsel);
> +void evsel__remove_from_group(struct evsel *evsel, struct evsel *leader);
>
> bool arch_evsel__must_be_in_group(const struct evsel *evsel);
>
> --
> 2.35.1
>