linux-kernel - Re: [PATCH 4/5] blk-mq: do limited block plug for multiple queue case

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 for Android: free password hash cracker in your pocket

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

Message-ID: <5547D815.7060100@fb.com>
Date:	Mon, 4 May 2015 14:35:33 -0600
From:	Jens Axboe <axboe@...com>
To:	Shaohua Li <shli@...com>
CC:	Jeff Moyer <jmoyer@...hat.com>, <linux-kernel@...r.kernel.org>,
	<hch@....de>, <neilb@...e.de>
Subject: Re: [PATCH 4/5] blk-mq: do limited block plug for multiple queue
 case

On 05/04/2015 02:33 PM, Shaohua Li wrote:
> On Mon, May 04, 2015 at 01:46:49PM -0600, Jens Axboe wrote:
>> On 05/04/2015 01:40 PM, Shaohua Li wrote:
>>> On Fri, May 01, 2015 at 04:16:04PM -0400, Jeff Moyer wrote:
>>>> Shaohua Li <shli@...com> writes:
>>>>
>>>>> plug is still helpful for workload with IO merge, but it can be harmful
>>>>> otherwise especially with multiple hardware queues, as there is
>>>>> (supposed) no lock contention in this case and plug can introduce
>>>>> latency. For multiple queues, we do limited plug, eg plug only if there
>>>>> is request merge. If a request doesn't have merge with following
>>>>> request, the requet will be dispatched immediately.
>>>>>
>>>>> This also fixes a bug. If we directly issue a request and it fails, we
>>>>> use blk_mq_merge_queue_io(). But we already assigned bio to a request in
>>>>> blk_mq_bio_to_request. blk_mq_merge_queue_io shouldn't run
>>>>> blk_mq_bio_to_request again.
>>>>
>>>> Good catch.  Might've been better to split that out first for easy
>>>> backport to stable kernels, but I won't hold you to that.
>>>
>>> It's not a severe bug, but I don't mind. Jens, please let me know if I
>>> should split the patch into 2 patches.
>>
>> I don't care that much for this particular case. But since one/more
>> of the others need respin anyway, might be prudent to split it up in
>> any case.
>
> ok, done. I'll repost the patch 4/5. Please let me know if I should
> repost 1-3.

That's fine, I'll grab 1-3 as-is. Thanks!

-- 
Jens Axboe

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/