Message-ID: <4B331CD6.1070207@cn.fujitsu.com>
Date: Thu, 24 Dec 2009 15:48:38 +0800
From: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
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To: Shaohua Li <shaohua.li@intel.com>
CC: linux-kernel@vger.kernel.org, jens.axboe@oracle.com, jmoyer@redhat.com,
       czoccolo@gmail.com, yanmin.zhang@intel.com
Subject: Re: cfq-iosched: tiobench regression
References: <20091224005506.GA7879@sli10-desk.sh.intel.com>
In-Reply-To: <20091224005506.GA7879@sli10-desk.sh.intel.com>
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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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