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Subject: Re: [PATCH -next 0/3] md/raid10: reduce lock contention for io
To:     Paul Menzel <pmenzel@molgen.mpg.de>,
        Yu Kuai <yukuai1@huaweicloud.com>
Cc:     song@kernel.org, linux-raid@vger.kernel.org,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20220829131502.165356-1-yukuai1@huaweicloud.com>
 <70172016-8ae5-92b8-2a43-8f0d4a2f6668@molgen.mpg.de>
 <0e22c51b-d36a-2216-4bfd-522049d3ed44@huaweicloud.com>
 <39f59994-cf2e-f8c4-fd57-988e8c7e05e5@molgen.mpg.de>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <1df89f4f-4e3a-8683-89c9-6e048ed79119@huaweicloud.com>
Date:   Wed, 31 Aug 2022 20:07:15 +0800
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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@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?
>>
>> 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(-)
> .
>