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To: des@des.no (=?iso-8859-1?q?Dag-Erling_Sm=F8rgrav?=)
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Mon, 22 Nov 2004 15:12:51 +0100."
             <xzpu0rigefw.fsf@dwp.des.no> 
Date: Mon, 22 Nov 2004 16:08:11 +0100
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cc: arch@freebsd.org
Subject: Re: anticipatory I/O scheduling 
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In message <xzpu0rigefw.fsf@dwp.des.no>, =?iso-8859-1?q?Dag-Erling_Sm=F8rgrav?=
 writes:
>I just ran across this paper and started wondering why I'd never heard
>of it before:
>
><URL:http://www.cs.rice.edu/~ssiyer/r/antsched/>
>
>To summarize, the authors rewrote the I/O scheduling algorithm in
>FreeBSD 4.3 and got massive performance improvements for Apache, and
>smaller but noticeable improvements for AFS and TPC-B.
>
>Has anyone looked into this?

Yes.

It's very hard to implement it correctly because you need a very
rapid timer (order of microseconds).

It is my plan to make disksort algorithms changeable on a per disk
basis to encourage experimentation in this area.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.