linux-kernel - Re: [Regression or Fix]perf: profiling stats sigificantly changed for aio_write/read(ext4) between 6.7.0-rc1 and 6.6.0

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Date:   Wed, 15 Nov 2023 08:26:06 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     David Wang <00107082@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
        acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        irogers@...gle.com, adrian.hunter@...el.com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Regression or Fix]perf: profiling stats sigificantly changed for
 aio_write/read(ext4) between 6.7.0-rc1 and 6.6.0

On Wed, Nov 15, 2023 at 8:12 AM David Wang <00107082@....com> wrote:
>
>
> 在 2023-11-15 23:48:33，"Namhyung Kim" <namhyung@...nel.org> 写道：
> >On Wed, Nov 15, 2023 at 3:00 AM David Wang <00107082@....com> wrote:
> >>
> >>
> >>
> >> At 2023-11-15 18:32:41, "Peter Zijlstra" <peterz@...radead.org> wrote:
> >> >
> >> >Namhyung, could you please take a look, you know how to operate this
> >> >cgroup stuff.
> >> >
> >>
> >> More information,  I run the profiling with 8cpu machine on a SSD with ext4 filesystem :
> >>
> >> # mkdir /sys/fs/cgroup/mytest
> >> # echo $$ > /sys/fs/cgroup/mytest/cgroup.procs
> >> ## Start profiling targeting cgroup /sys/fs/cgroup/mytest   on another terminal
> >> # fio --randrepeat=1 --ioengine=libaio --direct=1 --name=test  --bs=4k --iodepth=64 --size=1G --readwrite=randrw  --runtime=600 --numjobs=4 --time_based=1
> >>
> >> I got a feeling that f06cc667f7990 would decrease total samples by 10%~20% when profiling IO benchmark within cgroup.
> >
> >Oh sorry, I missed this message.  Can you please share the
> >command line and the output?
> >
> I did not use perf..... This is the part where  it is not quite convincing to report the change, I am using a profiling tool of my own as I mentioned in the first mail.....
> But I believe my profiling tools did detect some changes.

Oh.. ok.  You didn't use perf.

Then what is your profiling tool?  Where did you see
the 10%~20% drop in samples?

>
> I am not experienced with the perf-tool at all,   too complicated a tool for me.... But I think I can try it.

I feel sorry about that.  In most cases, just `perf record -a` and
then `perf report` would work well. :)

Thanks,
Namhyung