linux-kernel - Re: [PATCH] Don't wait if queue already has requests.

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] [day] [month] [year] [list]

Date:	Wed, 9 Feb 2011 14:43:04 +0100
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Justin TerAvest <teravest@...gle.com>
CC:	"vgoyal@...hat.com" <vgoyal@...hat.com>,
	"ctalbott@...gle.com" <ctalbott@...gle.com>,
	"mrubin@...gle.com" <mrubin@...gle.com>,
	"jmoyer@...hat.com" <jmoyer@...hat.com>,
	"guijianfeng@...fujitsu.com" <guijianfeng@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Don't wait if queue already has requests.

On 2011-02-09 14:15, Jens Axboe wrote:
> On 2011-02-08 20:18, Justin TerAvest wrote:
>> Commit 7667aa0630407bc07dc38dcc79d29cc0a65553c1 added logic to wait for
>> the last queue of the group to become busy (have at least one request),
>> so that the group does not lose out for not being continuously
>> backlogged. The commit did not check for the condition that the last
>> queue already has some requests. As a result, if the queue already has
>> requests, wait_busy is set. Later on, cfq_select_queue() checks the
>> flag, and decides that since the queue has a request now and wait_busy
>> is set, the queue is expired.  This results in early expiration of the
>> queue.
>>
>> This patch fixes the problem by adding a check to see if queue already
>> has requests. If it does, wait_busy is not set. As a result, time slices
>> do not expire early.
>>
>> The queues with more than one request are usually buffered writers.
>> Testing shows improvement in isolation between buffered writers.
> 
> Thanks for catching this in due time, I'll queue it up for 2.6.38 and

BTW, this was not meant as a snide remark, I initially thought the bad
commit was from dec 2010 when it is from 2009 :-)

-- 
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/