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

[Yu Kuai]

Hi, Paul!

在 2022/08/31 19:59, Paul Menzel 写道:
> Dear Yu,
>
>
> Am 30.08.22 um 03:09 schrieb Yu Kuai:
>
> > 在 2022/08/29 21:58, Paul Menzel 写道:
>
> > > 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.
>
> I was wondering about the model to be able to reproduce it.
>
> > > 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.
>
> Interesting. Maybe you could add all that to the commit message of the 
> second patch.

Of course, I will do that in next version.

Thanks,
Kuai
> Kind regards,
>
> Paul
>
>
> > > > 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(-)
> .