[PATCH v3 0/2] Fix cgroup metric association with BPF counters

[Ian Rogers <irogers@google.com>]

This series fixes an issue where cgroup metrics were not being correctly
associated and reported (showing `nan %`) when using BPF counters
(i.e., with `--bpf-counters`).

The root cause is that cgroup BPF counters only open the "leader" events
(for the first cgroup) and leave "follower" events unopened. Unopened
events have their `supported` flag set to `false` by default. During
metric calculation, `prepare_metric` checks `evsel->supported` and
discards the value (setting it to `NAN`) if it is `false`, leading to
`nan %` in the output.

The first patch fixes this by propagating the `supported` flag from the
leader events to the follower events in `bperf_load_program`.

The second patch adds a new shell test (`stat_metrics_cgrp.sh`) to
permanently cover this scenario (testing both with and without BPF
counters) and prevent regressions.

Reported-by: Svilen Kanev <skanev@google.com>

Changes since v2:
- Use `--metrics=insn_per_cycle` for the system-wide capability
  check in `check_system_wide` to ensure both cycles and instructions
  are supported.
- Use exact cgroup field matching with surrounding commas
  (`,${cgrp},`) in the `grep` check to prevent false positives when
  matching the root cgroup (`/`).
- Only enforce metric validation if both `cycles` and `instructions`
  counts are numeric and non-zero, preventing false failures on
  idle cgroups.
- Wrap long lines and fix trailing whitespace in the test script to
  comply with style guidelines.

Changes since v1:
- Fix commit message for patch 2 to remove the mention of
  insn_per_cycle check (which was simplified out).
- Quote variables in shell script to prevent word splitting.
- Use grep -F in shell script for literal matching of cgroup
  names containing dots.

Ian Rogers (2):
  perf stat: Propagate supported flag to follower cgroup BPF events
  perf test: Add stat metrics --for-each-cgroup test

 tools/perf/tests/shell/stat_metrics_cgrp.sh | 174 ++++++++++++++++++++
 tools/perf/util/bpf_counter_cgroup.c        |  15 ++
 2 files changed, 189 insertions(+)
 create mode 100755 tools/perf/tests/shell/stat_metrics_cgrp.sh

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2.54.0.631.ge1b05301d1-goog