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

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear Yu,


Thank you for your patches.

Am 29.08.22 um 15:14 schrieb Yu Kuai:
> 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

Could you please give more details about the test setup, like the drives 
used?

Did you use some tools like ftrace to figure out the bottleneck?

> 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(-)


Kind regards,

Paul