linux-kernel - Re: performance "regression" in cfq compared to anticipatory, deadline and noop

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Message-ID: <4826373B.8090408@cse.unsw.edu.au>
Date:	Sun, 11 May 2008 10:00:59 +1000
From:	Aaron Carroll <aaronc@....unsw.edu.au>
To:	Matthew <jackdachef@...il.com>
CC:	Fabio Checconi <fabio@...dalf.sssup.it>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	jens.axboe@...cle.com
Subject: Re: performance "regression" in cfq compared to anticipatory, deadline
 and noop

Matthew wrote:
>> 2) Does using a bigger value of slice_idle increase the throughput?
> 
> [..]
>
> 2) a bigger value even made it worse, setting it to "0" however
> seemingly "fixed" it, I however don't know how the overall
> effect/impact is, this will need some more real-world testing ;)

As Fabio said, you may lose throughput if you have multiple processes
with at least one sync. seq. reader.  However, for other workloads, you
should see a large global throughput improvement.  This is because CFQ
tends to idle without too much regard to thinktime or seekiness, often
wasting a few ms.  The trade-off is that your slow sync. processes may
suffer a little.

 -- Aaron
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