From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: unfair servicing of DomU vbd requests Date: Thu, 03 Mar 2011 08:30:07 +0000 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: James Harper , Ian Campbell Cc: xen devel List-Id: xen-devel@lists.xenproject.org On 03/03/2011 08:28, "James Harper" wrote: >>>> 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. Without the round-robin servicing, unfairness to the point of starvation is a distinct possibility. -- Keir > Thanks for looking at this. > > James