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perf stat: Propagate supported flag to follower cgroup BPF events

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When using BPF counters with cgroups, follower events (for cgroups
other than the first one) are not opened. Because they are not opened,
their `supported` flag was left as `false`.

During metric calculation, `prepare_metric` checks if the event is
supported. If it is not supported (like the follower events), it
explicitly sets the value to `NAN`, which eventually causes the metric
to be reported as `nan %`.

Fix this by propagating the `supported` flag from the "leader" events
(the ones opened for the first cgroup) to the "follower" events.

Also add a validation check to `bperf_load_program` to ensure `nr_cgroups`
is not zero and the number of events is a multiple of `nr_cgroups`,
preventing a potential division-by-zero (SIGFPE) exception when
`num_events` evaluates to 0 (e.g., with a trailing comma in cgroups list).

Reported-by: Svilen Kanev <skanev@google.com>
Assisted-by: Antigravity:gemini-3-flash
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Ian Rogers 2026-05-19 08:27:15 -07:00 committed by Arnaldo Carvalho de Melo
parent 7378b6656a
commit 65bd18199a
1 changed files with 20 additions and 0 deletions
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20
tools/perf/util/bpf_counter_cgroup.c
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@ -104,6 +104,11 @@ static int bperf_load_program(struct evlist *evlist)
set_max_rlimit();
if (nr_cgroups == 0 || evlist->core.nr_entries % nr_cgroups != 0) {
pr_err("Invalid cgroup or event count\n");
return -EINVAL;
}
test_max_events_program_load();
skel = bperf_cgroup_bpf__open();
@ -186,6 +191,21 @@ static int bperf_load_program(struct evlist *evlist)
i++;
}
/*
* Propagate supported flag from leaders to followers. Follower events
* are not opened, so their supported flag remains false.
*/
{
struct evsel *leader;
int num_events = evlist->core.nr_entries / nr_cgroups;
evlist__for_each_entry(evlist, evsel) {
leader = evlist__find_evsel(evlist, evsel->core.idx % num_events);
if (leader)
evsel->supported = leader->supported;
}
}
/*
* bperf uses BPF_PROG_TEST_RUN to get accurate reading. Check
* whether the kernel support it