linux-kernel - Re: [PATCHSET 0/6] perf tools: A couple of fixes for perf record --off-cpu (v1)

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Date:   Tue, 28 Jun 2022 11:40:32 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.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>,
        Milian Wolff <milian.wolff@...b.com>, bpf@...r.kernel.org,
        Blake Jones <blakejones@...gle.com>
Subject: Re: [PATCHSET 0/6] perf tools: A couple of fixes for perf record
 --off-cpu (v1)

Em Fri, Jun 24, 2022 at 04:13:07PM -0700, Namhyung Kim escreveu:
> Hello,
> 
> The first patch fixes a build error on old kernels which has
> task_struct->state field that is renamed to __state.  Actually I made
> a mistake when I wrote the code and assumed new kernel version.
> 
> The second patch is to prevent invalid sample synthesize by
> disallowing unsupported sample types.

So I'll pick the first two for perf/urgent and then when that is merged
into perf/core pick the rest, ok?

- Arnaldo
 
> The rest of the 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.
> 
> 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-v1' branch in my tree
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
> 
> Thanks,
> Namhyung
> 
> 
> Namhyung Kim (6):
>   perf offcpu: Fix a build failure on old kernels
>   perf offcpu: Accept allowed sample types only
>   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           | 60 +++++++++++++++++++++++--
>  tools/perf/util/bpf_skel/off_cpu.bpf.c  | 58 +++++++++++++++++++++---
>  tools/perf/util/evsel.c                 |  9 ++++
>  tools/perf/util/off_cpu.h               |  9 ++++
>  5 files changed, 176 insertions(+), 17 deletions(-)
> 
> 
> base-commit: 9886142c7a2226439c1e3f7d9b69f9c7094c3ef6
> -- 
> 2.37.0.rc0.161.g10f37bed90-goog

-- 

- Arnaldo