[PATCH -next 0/3] md/raid10: reduce lock contention for io

[Yu Kuai <yukuai1@huaweicloud.com>]

From: Yu Kuai <yukuai3@huawei.com>

patch 1 is a small problem found by code review.
patch 2 avoid holding resync_lock in fast path.
patch 3 avoid holding lock in wake_up() in fast path.

Test environment:

Architecture: aarch64
Cpu: Huawei KUNPENG 920, there are four numa nodes

Raid10 initialize:
mdadm --create /dev/md0 --level 10 --bitmap none --raid-devices 4 /dev/nvme0n1 /dev/nvme1n1 /dev/nvme2n1 /dev/nvme3n1

Test cmd:
fio -name=0 -ioengine=libaio -direct=1 -group_reporting=1 -randseed=2022 -rwmixread=70 -refill_buffers -filename=/dev/md0 -numjobs=16 -runtime=60s -bs=4k -iodepth=256 -rw=randread

Test result:
before this patchset:	2.9 GiB/s
after this patchset:	6.6 Gib/s

Please noted that in kunpeng-920, memory access latency is very bad
accross nodes compare to local node, and in other architecture
performance improvement might not be significant.

Yu Kuai (3):
  md/raid10: fix improper BUG_ON() in raise_barrier()
  md/raid10: convert resync_lock to use seqlock
  md/raid10: prevent unnecessary calls to wake_up() in fast path

 drivers/md/raid10.c | 88 +++++++++++++++++++++++++++++----------------
 drivers/md/raid10.h |  2 +-
 2 files changed, 59 insertions(+), 31 deletions(-)

-- 
2.31.1