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

[Yu Kuai]

Hi, Paul!

在 2022/08/29 21:58, Paul Menzel 写道:
> Dear Yu,
>
>
> Thank you for your patches.
>
> Am 29.08.22 um 15:14 schrieb Yu Kuai:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > 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?

test setup is described above, four nvme disks is used.
> Did you use some tools like ftrace to figure out the bottleneck?

Yes, I'm sure the bottleneck is spin_lock(), specifically threads from
multiple nodes try to grab the same lock. By the way, if I bind the
threads to the same node, performance can also improve to 6.6 Gib/s
without this patchset.

Thanks,
Kuai
> > 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
> .