linux-kernel - Re: deadline unfairness

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Message-ID: <47E4F6F7.40401@gelato.unsw.edu.au>
Date:	Sat, 22 Mar 2008 23:09:27 +1100
From:	Aaron Carroll <aaronc@...ato.unsw.edu.au>
To:	Bernd Schubert <bernd-schubert@....de>
CC:	linux-kernel@...r.kernel.org
Subject: Re: deadline unfairness

Bernd Schubert wrote:
> Hello,
> 
> some it seems the deadline scheduler is rather unfair. Below is an example
> of md-raid6 initialization of md3, md4 and md5. All three md-devices
> do share the same blockdevices (we have patched md to allow
> parallel rebuild of shared block devices, since for us the cpu is the 
> bottleneck and not the block device).
> 
> All rebuilds started basically at the same time, as you can see, md3 is already
> done and now md4 rebuilds substantially faster than md5.
> [..]
> This is basically with a 2.6.22 kernel + lustre + md-backports, but nothing
> done to the scheduler.

Hi Bernd,

There is a deadline bug in pre-2.6.24 kernels where lower-sector requests can starve
higher-sector requests; you might be hitting this bug.  It was fixed by commit:
    6f5d8aa6382eef2b26032c88656270bdae7f0c42


 -- Aaron


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