linux-kernel - [PATCH md-6.9 v2 00/10] md/raid1: refactor read

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Message-Id: <20240227120327.1432511-1-yukuai1@huaweicloud.com>
Date: Tue, 27 Feb 2024 20:03:17 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: xni@...hat.com,
	paul.e.luse@...ux.intel.com,
	song@...nel.org,
	shli@...com,
	neilb@...e.com
Cc: linux-raid@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai3@...wei.com,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com
Subject: [PATCH md-6.9 v2 00/10] md/raid1: refactor read_balance() and some minor fix

From: Yu Kuai <yukuai3@...wei.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/

Yu Kuai (10):
  md: add a new helper rdev_has_badblock()
  md/raid1: record nonrot rdevs while adding/removing rdevs to conf
  md/raid1: fix choose next idle in read_balance()
  md/raid1-10: add a helper raid1_check_read_range()
  md/raid1-10: factor out a new helper raid1_should_read_first()
  md/raid1: factor out read_first_rdev() from read_balance()
  md/raid1: factor out choose_slow_rdev() from read_balance()
  md/raid1: factor out choose_bb_rdev() from read_balance()
  md/raid1: factor out the code to manage sequential IO
  md/raid1: factor out helpers to choose the best rdev from
    read_balance()

 drivers/md/md.h       |  11 +
 drivers/md/raid1-10.c |  69 +++++++
 drivers/md/raid1.c    | 465 +++++++++++++++++++++++++-----------------
 drivers/md/raid1.h    |   1 +
 drivers/md/raid10.c   |  58 ++----
 drivers/md/raid5.c    |  35 ++--
 6 files changed, 391 insertions(+), 248 deletions(-)

-- 
2.39.2