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

[Paul Menzel]

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.


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(-)