[Xen-devel] Re: [Qemu-devel] [PATCH V12 05/17] xen: Add xenfv machine

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 12 Apr 2011, Jan Kiszka wrote:
> Well, either you have a use for the VCPU state (how do you do migration
> in Xen without it?), or you should probably teach QEMU in a careful &
> clean way to run its device model without VCPUs - and without any
> TCG-related memory consumption. For the latter, you would likely receive
> kudos from KVM people as well.
>
> BTW, if you happen to support that crazy vmport under Xen, not updating
> the VCPU state will break your neck. Also, lacking VCPUs prevent the
> usage of analysis and debugging features of QEMU (monitor, gdbstub).

We don't use the vcpu state in qemu because qemu takes care of device
emulation only; under xen the vcpu state is saved and restored by the
hypervisor.
We are currently using the number of vcpus just to know how many event
channels we have to bind to receive and send io notifications.
Thus your suggestion of teaching qemu to run without vcpus is probably
the right thing to do here.

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