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

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Date:   Thu, 11 Aug 2022 11:54:52 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        linux-perf-users@...r.kernel.org, Song Liu <songliubraving@...com>,
        Hao Luo <haoluo@...gle.com>,
        Blake Jones <blakejones@...gle.com>,
        Milian Wolff <milian.wolff@...b.com>, bpf@...r.kernel.org
Subject: [PATCH 0/4] Track processes properly for perf record --off-cpu (v2)

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