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

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Date:	Thu, 24 Dec 2009 15:48:38 +0800
From:	Gui Jianfeng <guijianfeng@...fujitsu.com>
To:	Shaohua Li <shaohua.li@...el.com>
CC:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com,
	jmoyer@...hat.com, czoccolo@...il.com, yanmin.zhang@...el.com
Subject: Re: cfq-iosched: tiobench regression

Shaohua Li wrote:
> We see about 30% regression in tiobench 32 threads 80M file sequential read.
> The regression is caused by below commits.
> 
> 5db5d64277bf390056b1a87d0bb288c8b8553f96
> The commit makes the slice too small. In the test, the slice is limitted
> to 2 * idle_slice(300ms/32 < 2*idle_slice). This dramatically impacts io
> thoughput. The low_latency knob used to be only impact random io, now it
> impacts sequential io too. Any idea to fix it?

Hi Shaohua,

IMHO this shouldn't be a problem. Currently, low_latency is used to improve
the latency for the whole system. If someone would like to achieve high throughput,
just turn off low_latency knob.

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