This covers two different use cases.  The first one is cgroup
filtering given by -G/--cgroup option which controls the off-cpu
profiling for tasks in the given cgroups only.

The other use case is cgroup sampling which is enabled by
--all-cgroups option and it adds PERF_SAMPLE_CGROUP to the sample_type
to set the cgroup id of the task in the sample data.

Example output.

  $ sudo perf record -a --off-cpu --all-cgroups sleep 1

  $ sudo perf report --stdio -s comm,cgroup --call-graph=no
  ...
  # Samples: 144  of event 'offcpu-time'
  # Event count (approx.): 48452045427
  #
  # Children      Self  Command          Cgroup
  # ........  ........  ...............  ..........................................
  #
      61.57%     5.60%  Chrome_ChildIOT  /user.slice/user-657345.slice/user@657345.service/app.slice/...
      29.51%     7.38%  Web Content      /user.slice/user-657345.slice/user@657345.service/app.slice/...
      17.48%     1.59%  Chrome_IOThread  /user.slice/user-657345.slice/user@657345.service/app.slice/...
      16.48%     4.12%  pipewire-pulse   /user.slice/user-657345.slice/user@657345.service/session.slice/...
      14.48%     2.07%  perf             /user.slice/user-657345.slice/user@657345.service/app.slice/...
      14.30%     7.15%  CompositorTileW  /user.slice/user-657345.slice/user@657345.service/app.slice/...
      13.33%     6.67%  Timer            /user.slice/user-657345.slice/user@657345.service/app.slice/...
  ...
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Blake Jones <blakejones@google.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20220518224725.742882-6-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>