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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 21 Aug 2019 09:04:57 +0800
From:   Joseph Qi <joseph.qi@...ux.alibaba.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Jan Kara <jack@...e.cz>, Joseph Qi <jiangqi903@...il.com>,
        Dave Chinner <david@...morbit.com>,
        Andreas Dilger <adilger@...ger.ca>,
        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"

Hi Ted，

On 19/8/21 00:08, Theodore Y. Ts'o wrote:
> On Tue, Aug 20, 2019 at 11:00:39AM +0800, Joseph Qi wrote:
>>
>> I've tested parallel dio reads with dioread_nolock, it doesn't have
>> significant performance improvement and still poor compared with reverting
>> parallel dio reads. IMO, this is because with parallel dio reads, it take
>> inode shared lock at the very beginning in ext4_direct_IO_read().
> 
> Why is that a problem?  It's a shared lock, so parallel threads should
> be able to issue reads without getting serialized?
> 
The above just tells the result that even mounting with dioread_nolock,
parallel dio reads still has poor performance than before (w/o parallel
dio reads).

> Are you using sufficiently fast storage devices that you're worried
> about cache line bouncing of the shared lock?  Or do you have some
> other concern, such as some other thread taking an exclusive lock?
> 
The test case is random read/write described in my first mail. And
from my preliminary investigation, shared lock consumes more in such
scenario.

Thanks,
Joseph