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RE: [Xen-devel] unfair servicing of DomU vbd requests

To: "Ian Campbell" <Ian.Campbell@xxxxxxxxxx>, "Keir Fraser" <keir.xen@xxxxxxxxx>
Subject: RE: [Xen-devel] unfair servicing of DomU vbd requests
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Thu, 3 Mar 2011 19:28:29 +1100
Cc: xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] unfair servicing of DomU vbd requests
> > > It appears that Dom0 is not servicing vbd requests from DomU's fairly so
> > > one or two end up getting stalled while the others are mostly okay. How
> > > are vbd requests supposed to be serviced? Is there potential for one to
> > > be overlooked for a long period of time? Is there some settings that
> > > could be changed to avoid this happening?
> >
> > Dom0 does round-robin scanning of pending event channels these days, which
> > helps fairness a fair bit.
> 
> I have a feeling this isn't true of pvops kernels...
> 
> looks like we need to pull 324:7fe1c6d02a2b (and subsequent fixes) out
> of 2.6.18-xen.hg into the pvops world.
> 

I hope that's true and easy to fix. It would certainly explain why one DomU can 
starve enough to the point where it's IO doesn't get serviced for >70 seconds.

Thanks for looking at this.

James
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