Re: deadline unfairness

[Aaron Carroll <aaronc@gelato.unsw.edu.au>]

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