linux-kernel - Re: cfq-iosched: a regression

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Message-ID: <4E4E03D5.40404@fusionio.com>
Date:	Fri, 19 Aug 2011 08:33:57 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Shaohua Li <shaohua.li@...el.com>
CC:	"teravest@...gle.com" <teravest@...gle.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"Shi, Alex" <alex.shi@...el.com>
Subject: Re: cfq-iosched: a regression

On 2011-08-16 04:47, Shaohua Li wrote:
> We have a kernel build regression since 3.1-rc1, which is about 10%
> regression. The kernel source is in an ext3 filesystem.
> Alex Shi bisect it to commit:
> commit a07405b7802691d29ab3b23bdc76ee6d006aad0b
> Author: Justin TerAvest <teravest@...gle.com>
> Date:   Sun Jul 10 22:09:19 2011 +0200
> 
>     cfq: Remove special treatment for metadata rqs.
> 
> Apparently this is caused by lack metadata preemption, where ext3/ext4
> do use READ_META. I didn't see a way to fix the issue, so suggest
> reverting the patch.
> 
> Reported-by: Alex Shi<alex.shi@...el.com>
> Reported-by: Shaohua Li<shaohua.li@...el.com>

I had a gut feeling on that meta data, it's hard to know exactly where
it helps at this point. I'll revert the commit and then we can diagnose
this on the side.

-- 
Jens Axboe

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