[PATCH 0/4] Track processes properly for perf record --off-cpu (v2)

[Namhyung Kim]

Hello,

This patch series implements inheritance of offcpu events for the
child processes.  Unlike perf events, BPF cannot know which task it
should track except for ones set in a BPF map at the beginning.  Add
another BPF program to the fork path and add the process id to the map
if the parent is tracked.

Changes in v2)
 * drop already merged fixes
 * fix the shell test to omit noises
 
With this change, it can get the correct off-cpu events for child
processes.  I've tested it with perf bench sched messaging which
creates a lot of processes.

  $ sudo perf record -e dummy --off-cpu -- perf bench sched messaging
  # Running 'sched/messaging' benchmark:
  # 20 sender and receiver processes per group
  # 10 groups == 400 processes run

       Total time: 0.196 [sec]
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.178 MB perf.data (851 samples) ]


  $ sudo perf report --stat | grep -A1 offcpu
  offcpu-time stats:
            SAMPLE events:        851

The benchmark passes messages by read/write and it creates off-cpu
events.  With 400 processes, we can see more than 800 events.

The child process tracking is also enabled when -p option is given.
But -t option does NOT as it only cares about the specific threads.
It may be different what perf_event does now, but I think it makes
more sense.

You can get it from 'perf/offcpu-child-v2' branch in my tree

  https://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git

Thanks,
Namhyung


Namhyung Kim (4):
  perf offcpu: Check process id for the given workload
  perf offcpu: Parse process id separately
  perf offcpu: Track child processes
  perf offcpu: Update offcpu test for child process

 tools/perf/tests/shell/record_offcpu.sh | 57 ++++++++++++++++++++++---
 tools/perf/util/bpf_off_cpu.c           | 53 ++++++++++++++++++++++-
 tools/perf/util/bpf_skel/off_cpu.bpf.c  | 38 ++++++++++++++++-
 3 files changed, 138 insertions(+), 10 deletions(-)


base-commit: b39c9e1b101d2992de9981673919ae55a088792c
-- 
2.37.1.595.g718a3a8f04-goog