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Re: [Qemu-devel] cpuid problem in upstream qemu with kvm

From: Daniel P. Berrange
Subject: Re: [Qemu-devel] cpuid problem in upstream qemu with kvm
Date: Thu, 7 Jan 2010 12:47:38 +0000
User-agent: Mutt/1.4.1i

On Thu, Jan 07, 2010 at 02:40:34PM +0200, Avi Kivity wrote:
> On 01/07/2010 02:33 PM, Anthony Liguori wrote:
> >
> >There's another option.
> >
> >Make cpuid information part of live migration protocol, and then 
> >support something like -cpu Xeon-3550.  We would remember the exact 
> >cpuid mask we present to the guest and then we could validate that we 
> >can obtain the same mask on the destination.
> Currently, our policy is to only migrate dynamic (from the guest's point 
> of view) state, and specify static state on the command line [1].
> I think your suggestion makes a lot of sense, but I'd like to expand it 
> to move all guest state, whether dynamic or static.  So '-m 1G' would be 
> migrated as well (but not -mem-path).  Similarly, in -drive 
> file=...,if=ide,index=1, everything but file=... would be migrated.
> This has an advantage wrt hotplug: since qemu is responsible for 
> migrating all guest visible information, the migrator is no longer 
> responsible for replaying hotplug events in the exact sequence they 
> happened.

With the introduction of the new -device spport, there's no need to
replay hotplug events in order any more. Instead just use static
PCI addresses when starting the guest, and the same addresses after
migration. You could argue that QEMU should preserve the addressing
automatically during migration, but apps need to do it manually
already to keep addreses stable across power-offs, so doing it manually
across migration too is no extra burden.

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