linux-kernel - Re: [PATCH V2 1/2] block: Make cfq_target

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Message-ID: <4F78C9C3.3090203@kernel.dk>
Date:	Sun, 01 Apr 2012 14:33:55 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Tao Ma <tm@....ma>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 1/2] block: Make cfq_target_latency tunable through
 sysfs.

On 2012-03-31 08:31, Tao Ma wrote:
> From: Tao Ma <boyu.mt@...bao.com>
> 
> In cfq, when we calculate a time slice for a process(or a cfqq to
> be precise), we have to consider the cfq_target_latency so that all the
> sync request have an estimated latency(300ms) and it is controlled by
> cfq_target_latency. But in some hadoop test, we have found that if
> there are many processes doing sequential read(24 for example), the
> throughput is bad because every process can only work for about 25ms
> and the cfqq is switched. That leads to a higher disk seek. We can
> achive the good throughput by setting low_latency=0, but then some
> read's latency is too much for the application.
> 
> So this patch makes cfq_target_latency tunable through sysfs so that
> we can tune it and find some magic number which is not bad for both
> the throughput and the read latency.

Thanks, applied both.

-- 
Jens Axboe

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