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From:   Song Liu <song@kernel.org>
Date:   Tue, 20 Jun 2023 10:17:48 -0700
Message-ID: <CAPhsuW7=W4DRBOjeeJ5MSQR5ZWXZ6745FTd-Dj_qsP-KwxTUmQ@mail.gmail.com>
Subject: Re: [PATCH] raid10: avoid spin_lock from fastpath from raid10_unplug()
To:     Yu Kuai <yukuai1@huaweicloud.com>
Cc:     Paul Menzel <pmenzel@molgen.mpg.de>, aligrudi@gmail.com,
        linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, yangerkun@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
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On Mon, Jun 19, 2023 at 6:00=E2=80=AFAM Yu Kuai <yukuai1@huaweicloud.com> w=
rote:
>
> Hi,
>
> =E5=9C=A8 2023/06/19 18:26, Paul Menzel =E5=86=99=E9=81=93:
> > Dear Yu,
> >
> >
> > Thank you for your patch. Some minor nits from my side, you can also
> > ignore.
> >
> > Am 18.06.23 um 16:25 schrieb Yu Kuai:
> >> From: Yu Kuai <yukuai3@huawei.com>
> >>
> >> Commit 0c0be98bbe67 ("md/raid10: prevent unnecessary calls to wake_up(=
)
> >> in fast path") missed one place, for example, while testing with:
> >
> > =E2=80=A6 one place. For example, with
> >
> >>
> >> fio -direct=3D1 -rw=3Dwrite/randwrite -iodepth=3D1 ...
> >>
> >> Then plug and unplug will be called for each io, then wake_up() from
> >
> > Maybe:
> >
> >      fio -direct=3D1 -rw=3Dwrite/randwrite -iodepth=3D1 ...
> >
> > plug und unplug are called for each io, then =E2=80=A6
> >
> >> raid10_unplug() will cause lock contention as well.
> >
> > Maybe paste the perf command and output?
>
> Related test and test result and perf result can be found in the below
> Link.

We don't need a lot of details of the test results in the commit log. But a
quick summary of the performance result can be really helpful here.
Something like: on array X, fio job Y, before the patch we got AAA, with
the patch, we got BBB.

Other than this, the patch looks good to me.

Thanks,
Song