linux-ext4 - Re: [RFC] performance regression with "ext4: Allow parallel DIO reads"

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Date:   Fri, 26 Jul 2019 09:12:07 +0800
From:   Joseph Qi <joseph.qi@...ux.alibaba.com>
To:     Andreas Dilger <adilger@...ger.ca>,
        Joseph Qi <jiangqi903@...il.com>, Theodore Ts'o <tytso@....edu>
Cc:     Jan Kara <jack@...e.cz>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>,
        Liu Bo <bo.liu@...ux.alibaba.com>
Subject: Re: [RFC] performance regression with "ext4: Allow parallel DIO
 reads"



On 19/7/26 05:20, Andreas Dilger wrote:
> 
>> On Jul 23, 2019, at 5:17 AM, Joseph Qi <jiangqi903@...il.com> wrote:
>>
>> Hi Ted & Jan,
>> Could you please give your valuable comments?
> 
> It seems like the original patches should be reverted?  There is no data

>From my test result, yes.
I've also tested libaio with iodepth 16, it behaves the same. Here is the test
data for libaio 4k randrw:

-------------------------------------------------------------------------------------------
w/ parallel dio reads | READ 78313KB/s, 19578, 1698.70us  | WRITE 78313KB/s, 19578, 4837.60us
-------------------------------------------------------------------------------------------
w/o parallel dio reads| READ 387774KB/s, 96943, 1009.73us | WRITE 387656KB/s，96914, 308.87us
-------------------------------------------------------------------------------------------

Since this commit went into upstream long time ago，to be precise, Linux
4.9, I wonder if someone else has also observed this regression, or
anything I missed?

Thanks,
Joseph

> in the original commit message that indicates there is an actual performance
> improvement from that patch, but there is data here showing it hurts both
> read and write performance quite significantly.
> > Cheers, Andreas
> 
>> On 19/7/19 17:22, Joseph Qi wrote:
>>> Hi Ted & Jan,
>>> I've observed an significant performance regression with the following
>>> commit in my Intel P3600 NVMe SSD.
>>> 16c54688592c ext4: Allow parallel DIO reads
>>>
>>> From my initial investigation, it may be because of the
>>> inode_lock_shared (down_read) consumes more than inode_lock (down_write)
>>> in mixed random read write workload.
>>>
>>> Here is my test result.
>>>
>>> ioengine=psync
>>> direct=1
>>> rw=randrw
>>> iodepth=1
>>> numjobs=8
>>> size=20G
>>> runtime=600
>>>
>>> w/ parallel dio reads : kernel 5.2.0
>>> w/o parallel dio reads: kernel 5.2.0, then revert the following commits:
>>>  1d39834fba99 ext4: remove EXT4_STATE_DIOREAD_LOCK flag (related)
>>>  e5465795cac4 ext4: fix off-by-one error when writing back pages before dio read (related)
>>>  16c54688592c ext4: Allow parallel DIO reads
>>>
>>> bs=4k:
>>> -------------------------------------------------------------------------------------------
>>> w/ parallel dio reads | READ 30898KB/s, 7724, 555.00us   | WRITE 30875KB/s, 7718, 479.70us
>>> -------------------------------------------------------------------------------------------
>>> w/o parallel dio reads| READ 117915KB/s, 29478, 248.18us | WRITE 117854KB/s，29463, 21.91us
>>> -------------------------------------------------------------------------------------------
>>>
>>> bs=16k:
>>> -------------------------------------------------------------------------------------------
>>> w/ parallel dio reads | READ 58961KB/s, 3685, 835.28us   | WRITE 58877KB/s, 3679, 1335.98us
>>> -------------------------------------------------------------------------------------------
>>> w/o parallel dio reads| READ 218409KB/s, 13650, 554.46us | WRITE 218257KB/s，13641, 29.22us
>>> -------------------------------------------------------------------------------------------
>>>
>>> bs=64k:
>>> -------------------------------------------------------------------------------------------
>>> w/ parallel dio reads | READ 119396KB/s, 1865, 1759.38us | WRITE 119159KB/s, 1861, 2532.26us
>>> -------------------------------------------------------------------------------------------
>>> w/o parallel dio reads| READ 422815KB/s, 6606, 1146.05us | WRITE 421619KB/s, 6587, 60.72us
>>> -------------------------------------------------------------------------------------------
>>>
>>> bs=512k:
>>> -------------------------------------------------------------------------------------------
>>> w/ parallel dio reads | READ 392973KB/s, 767, 5046.35us  | WRITE 393165KB/s, 767, 5359.86us
>>> -------------------------------------------------------------------------------------------
>>> w/o parallel dio reads| READ 590266KB/s, 1152, 4312.01us | WRITE 590554KB/s, 1153, 2606.82us
>>> -------------------------------------------------------------------------------------------
>>>
>>> bs=1M:
>>> -------------------------------------------------------------------------------------------
>>> w/ parallel dio reads | READ 487779KB/s, 476, 8058.55us  | WRITE 485592KB/s, 474, 8630.51us
>>> -------------------------------------------------------------------------------------------
>>> w/o parallel dio reads| READ 593927KB/s, 580, 7623.63us  | WRITE 591265KB/s, 577, 6163.42us
>>> -------------------------------------------------------------------------------------------
>>>
>>> Thanks,
>>> Joseph
>>>
> 
> 
> Cheers, Andreas
> 
> 
> 
> 
>