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Subject: Re: [RFC] performance regression with "ext4: Allow parallel DIO
 reads"
To:     Jan Kara <jack@suse.cz>, Joseph Qi <jiangqi903@gmail.com>
Cc:     Dave Chinner <david@fromorbit.com>,
        Andreas Dilger <adilger@dilger.ca>,
        Theodore Ts'o <tytso@mit.edu>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>,
        Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>,
        Liu Bo <bo.liu@linux.alibaba.com>
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 <15112e38-94fe-39d6-a8e2-064ff47187d5@linux.alibaba.com>
 <20190728225122.GG7777@dread.disaster.area>
 <960bb915-20cc-26a0-7abc-bfca01aa39c0@gmail.com>
 <20190815151336.GO14313@quack2.suse.cz>
From:   Joseph Qi <joseph.qi@linux.alibaba.com>
Message-ID: <075fd06f-b0b4-4122-81c6-e49200d5bd17@linux.alibaba.com>
Date:   Fri, 16 Aug 2019 21:23:24 +0800
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Hi Jan,
Thanks for your reply.

On 19/8/15 23:13, Jan Kara wrote:
> On Tue 30-07-19 09:34:39, Joseph Qi wrote:
>> On 19/7/29 06:51, Dave Chinner wrote:
>>> On Fri, Jul 26, 2019 at 09:12:07AM +0800, Joseph Qi wrote:
>>>>
>>>>
>>>> On 19/7/26 05:20, Andreas Dilger wrote:
>>>>>
>>>>>> On Jul 23, 2019, at 5:17 AM, Joseph Qi <jiangqi903@gmail.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?
>>>
>>> I suspect that the second part of this set of mods that Jan had
>>> planned to do (on the write side to use shared locking as well)
>>> did not happen and so the DIO writes are serialising the workload.
>>>
>>
>> Thanks for the inputs, Dave.
>> Hi Jan, Could you please confirm this?
>> If so, should we revert this commit at present?
> 
> Sorry for getting to you only now. I was on vacation and then catching up
> with various stuff. I suppose you are not using dioread_nolock mount
> option, are you? Can you check what are your results with that mount
> option?
> 
Yes, I've just used default mount options when testing. And it is indeed
that there is performance improvement with dioread_nolock after reverting
the 3 related commits.
I'll do a supplementary test with parallel dio reads as well as
dioread_nolock and send out the test result.

> I have hard time remembering what I was thinking those couple years back
> but I think the plan was to switch to dioread_nolock always but somehow I
> didn't finish that and now I forgot where I got stuck because I don't see
> any problem with that currently.
Do you mean mark dioread_nolock as default?

Thanks,
Joseph
> 
> 								Honza
>