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Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions |
Date: |
Wed, 10 Jun 2009 21:07:56 +0300 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
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
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, (continued)
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Paul Brook, 2009/06/10
- Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions, Michael S. Tsirkin, 2009/06/11