This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


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>
Delivery-date: Thu, 03 Mar 2011 00:29:21 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <1299140560.17907.1794.camel@xxxxxxxxxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <C994F3F3.14124%keir.xen@xxxxxxxxx> <1299140560.17907.1794.camel@xxxxxxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcvZfDImqvppAhhmRFmohKisMzL9KQAACsow
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.

Xen-devel mailing list