Re: [Qemu-devel] [libvirt] Modern CPU models cannot be used with libvirt

[Anthony Liguori <anthony@codemonkey.ws>]

On 03/25/2012 08:21 AM, Avi Kivity wrote:
> On 03/11/2012 04:12 PM, Anthony Liguori wrote:
>> This discussion isn't about whether QEMU should have a Westmere
>> processor definition.  In fact, I think I already applied that patch.
>>
>> It's a discussion about how we handle this up and down the stack.
>>
>> The question is who should define and manage CPU compatibility.  Right
>> now QEMU does to a certain degree, libvirt discards this and does it's
>> own thing, and VDSM/ovirt-engine assume that we're providing something
>> and has built a UI around it.
>>
>> What I'm proposing we consider: have VDSM manage CPU definitions in
>> order to provide a specific user experience in ovirt-engine.
>>
>> We would continue to have Westmere/etc in QEMU exposed as part of the
>> user configuration.  But I don't think it makes a lot of sense to have
>> to modify QEMU any time a new CPU comes out.
>
> We have to.  New features often come with new MSRs which need to be live
> migrated, and of course the cpu flags as well.  We may push all these to
> qemu data files, but this is still qemu.  We can't let a management tool
> decide that cpu feature X is safe to use on qemu version Y.

I think QEMU should own CPU definitions.  I think a management tool should have 
the choice of whether they are used though because they are a policy IMHO.

It's okay for QEMU to implement some degree of policy as long as a management 
tool can override it with a different policy.

Regards,

Anthony Liguori

>