On 16 Apr 2009 at 17:17, Bart Van Assche wrote:

> 
> On Thu, Apr 16, 2009 at 2:07 PM, Pasi Kärkkäinen <pa...@iki.fi> wrote:
> > Iirc it has been with RHEL5/CentOS5 2.6.18 based kernels..
> >
> > Mike Christie has been writing about this aswell.. dunno about what kernels
> > he has seen it with.
> >
> > Then again CFQ was designed for "single disk workstations"..
> 
> I have seen the above statement about CFQ only once in the past, and
> that was in this post:
> http://www.mail-archive.com/cen...@centos.org/msg04648.html. But if
> CFQ really was designed for single disk workstations, I do not
> understand why it has been chosen as the default in Red Hat Enterprise
> Linux 4. There must have been a good reason behind that choice.

>From what I know and what I've read (e.g. Deitel, Operating Systems, 3rd 
>edition, 
Case Study: Linux), the I/O scheduler manages requests per device, and the CFQ 
has 
the advantage (over the default elevator algorithm) that it avoids starvation 
of 
requests. This may have the consequence that disk channel throughput is sub-
optimal.

Regards,
Ulrich


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