From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MESGS-0004nq-CH for qemu-devel@nongnu.org; Wed, 10 Jun 2009 14:11:08 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MESGP-0004m7-0E for qemu-devel@nongnu.org; Wed, 10 Jun 2009 14:11:08 -0400 Received: from [199.232.76.173] (port=52696 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MESGO-0004m0-CX for qemu-devel@nongnu.org; Wed, 10 Jun 2009 14:11:04 -0400 Received: from mx2.redhat.com ([66.187.237.31]:57500) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MESGN-0006Z0-TA for qemu-devel@nongnu.org; Wed, 10 Jun 2009 14:11:04 -0400 Date: Wed, 10 Jun 2009 21:07:56 +0300 From: "Michael S. Tsirkin" Subject: Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions Message-ID: <20090610180756.GM28601@redhat.com> References: <200906101746.06740.paul@codesourcery.com> <20090610170306.GL28601@redhat.com> <200906101830.21537.paul@codesourcery.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200906101830.21537.paul@codesourcery.com> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paul Brook Cc: Carsten Otte , kvm@vger.kernel.org, Rusty Russell , qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, Blue Swirl , Christian Borntraeger , Avi Kivity On Wed, Jun 10, 2009 at 06:30:16PM +0100, Paul Brook wrote: > On Wednesday 10 June 2009, Michael S. Tsirkin wrote: > > On Wed, Jun 10, 2009 at 05:46:03PM +0100, Paul Brook wrote: > > > > > If you can't create an identical machine from scratch then I don't > > > > > consider snapshot/migration to be a useful feature. i.e. as soon as > > > > > you shutdown and restart the guest it is liable to break anyway. > > > > > > > > Why is liable to break? > > > > > > A VM booted on an old version of qemu and migrated to a new version will > > > behave differently to a the same VM booted on a new version of qemu. > > > > It will behave identically. That's what the patch does: discover > > how did the device behave on old qemu, and make it behave the same way > > on new qemu. > > You're missing the point. After doing a live migration from old-qemu to new- > qemu, there is no snapshot to load. We need to be able to shutdown the guest, > kill qemu (without saving a snapshot), then start qemu with the exact same > hardware. Yes, I see how this would sometimes be useful. So this feature request would mean that we need a flag to disable msix in virtio net. I think we can agree that hardware can change across reboots. It can with real hardware and it happens without guest doing anything. > If we can't start a new qemu with the same hardware configuration then we > should not be allowing migration or loading of snapshots. > > Paul OK, so I'll add an option in virtio-net to disable msi-x, and such an option will be added in any device with msi-x support. Will that address your concern? -- MST