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

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Date:   Thu, 11 Aug 2022 17:58:27 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        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: Re: [PATCH 0/4] Track processes properly for perf record --off-cpu
 (v2)

Em Thu, Aug 11, 2022 at 11:54:52AM -0700, Namhyung Kim escreveu:
> 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.

Thanks for resubmitting, applied!

Will be up in perf/core as soon as tests finish.

- Arnaldo
 
> 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

-- 

- Arnaldo