Re: [Qemu-devel] Re: [PATCH v2 9/9] Add -kvm option

[Anthony Liguori]

Avi Kivity wrote:
> On 10/08/2009 04:23 PM, Anthony Liguori wrote:
> > > > What I'd like to see in the interim is a kvm specific machine type 
> > > > that's defaulted to if kvm is enabled.  I think this would be 
> > > > useful not only for enabling things like in-kernel apic, but also 
> > > > for selecting a default cpu model.
> > >
> > > We should make a distinction between guest-visible changes and 
> > > accelerators like kvm-irqchip and vhost.
> >
> > They are different device models that happen to implement the same 
> > guest-visible device. 
>
> I think this separation is artificial.  From both the guest's view and 
> the user's view, there's no difference between qemu ioapic and kvm 
> ioapic (modulo bugs).  To me this indicates they're the same device.

That's not always been true historically.  For instance, the in-kernel 
pit does interrupt catchup whereas the userspace pit does not.

> We'll have the same problem with vhost-net, only there the duplication 
> will be much greater if we split the implementation.

I'd rather not treat vhost-net like a device model and instead treat it 
like a -net backend.  If we can bounce requests through userspace (and 
we can), we should be able to use it for any device model.  In the case 
of virtio-net, we should be able to short-circuit things such that we 
don't have to go through userspace.  It's admittedly very hairy without 
a point-to-point net abstraction.

Regards,

Anthony Liguori