linux-ext4 - Re: [GIT PULL] Ext3 latency fixes

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Date:	Sat, 4 Apr 2009 16:33:49 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Theodore Tso <tytso@....edu>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [GIT PULL] Ext3 latency fixes

On Sat, 4 Apr 2009 19:22:22 -0400
Theodore Tso <tytso@....edu> wrote:
> 
> However, the full latency fixes all the writes are synchronous, so it
> must be the case that the delays are caused by the fact that queue is
> getting implicitly unplugged after the synchronous write, and the
> problem is no longer the mixing of WRITE and WRITE_SYNC requests as
> posted in the commit log for 78f707bf.  If we remove the automatic
> unplug for WRITE_SYNC requests, and add an explicit unplug where it is
> needed, that should fix the performance regression for this particular
> sqlite test case. 

removing the unplug is bound to be bad; after all we're waiting on the
IO. But maybe it should be "make the unplug a REALLY short time".
At least for rotating storage. For non-rotating .. I'd never wait.

-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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