From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: poor domU VBD performance. Date: Thu, 31 Mar 2005 17:39:26 +0200 Message-ID: <20050331153925.GP9204@suse.de> References: <20050331070514.GH9204@suse.de> <20050331071043.GI9204@suse.de> <63537e2b84ddbba6cb3d970f73c6ab35@cl.cam.ac.uk> <20050331081900.GK9204@suse.de> <20050331143312.GB13179@vienna.egenera.com> <20050331153449.GE12579@tpkurt.garloff.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20050331153449.GE12579@tpkurt.garloff.de> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Kurt Garloff Cc: Ian Pratt , Philip R Auld , Xen development list , Vincent Hanquez , Christian Limpach List-Id: xen-devel@lists.xenproject.org On Thu, Mar 31 2005, Kurt Garloff wrote: > Hi, > > On Thu, Mar 31, 2005 at 09:33:12AM -0500, Philip R Auld wrote: > > This effects merging though, right? I don't think the the front > > end has done any merging. > > The noop elevator does front and back merging. > My understanding is that it's used in the frontend driver. > > Otherwise, unplugging on every block would indeed be quite bad ... Not necessarily - either your io rate is not fast enough to sustain a substantial queue depth, in that case you get plugging on basically every io anyways. If on the other hand the io rate is high enough to maintain a queue depth of > 1, then the plugging will never take place because the queue never empties. So all in all, I don't think the temporary work-around will be such a bad idea. I would still rather implement the queue tracking though, it should not be more than a few lines of code. And Philip, I will get the bio_sync() change merged :-) -- Jens Axboe