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From: Song Liu <song@kernel.org>
Date: Tue, 27 Feb 2024 13:11:26 -0800
Message-ID: <CAPhsuW4PRcbQbjoXQ_F=V4DxAJp9v_ybWHgwueCLA+iU52J7mQ@mail.gmail.com>
Subject: Re: [PATCH md-6.9 v2 00/10] md/raid1: refactor read_balance() and
 some minor fix
To: Yu Kuai <yukuai1@huaweicloud.com>
Cc: xni@redhat.com, paul.e.luse@linux.intel.com, shli@fb.com, neilb@suse.com, 
	linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai3@huawei.com, 
	yi.zhang@huawei.com, yangerkun@huawei.com
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On Tue, Feb 27, 2024 at 4:09=E2=80=AFAM Yu Kuai <yukuai1@huaweicloud.com> w=
rote:
>
> From: Yu Kuai <yukuai3@huawei.com>
>
> Changes in v2:
>  - add new conter in conf for patch 2;
>  - fix the case choose next idle while there is no other idle disk in
>  patch 3;
>  - add some review tag from Xiao Ni for patch 1, 4-8
>
> The original idea is that Paul want to optimize raid1 read
> performance([1]), however, we think that the original code for
> read_balance() is quite complex, and we don't want to add more
> complexity. Hence we decide to refactor read_balance() first, to make
> code cleaner and easier for follow up.
>
> Before this patchset, read_balance() has many local variables and many
> branches, it want to consider all the scenarios in one iteration. The
> idea of this patch is to divide them into 4 different steps:
>
> 1) If resync is in progress, find the first usable disk, patch 5;
> Otherwise:
> 2) Loop through all disks and skipping slow disks and disks with bad
> blocks, choose the best disk, patch 10. If no disk is found:
> 3) Look for disks with bad blocks and choose the one with most number of
> sectors, patch 8. If no disk is found:
> 4) Choose first found slow disk with no bad blocks, or slow disk with
> most number of sectors, patch 7.
>
> Note that step 3) and step 4) are super code path, and performance
> should not be considered.
>
> And after this patchset, we'll continue to optimize read_balance for
> step 2), specifically how to choose the best rdev to read.
>
> [1] https://lore.kernel.org/all/20240102125115.129261-1-paul.e.luse@linux=
intel.com/

v2 looks good to me. Thanks! I will give Xiao some more time to review
it one more time before pushing it to md-6.9.

Song