Re: xen drivers to use virtio?

[Jeremy Fitzhardinge <jeremy@goop.org>]

Anthony Liguori wrote:
> Jeremy Fitzhardinge wrote:
>> Jun Koi wrote:
>>> If I understand correctly, we are going to rewrite some xen drivers in
>>> Linux kernel to use virtio once virtio is stable. Is that true?
>>>   
>>
>> There are no plans to do so.
>
> Actually, they're already there to some degree now that qemu-dm is 
> tracking the upstream QEMU tree.  virtio support has been in the QEMU 
> tree for some time now.  If it's not enabled in qemu-dm by default, it 
> should be trivial to enable.  From Xend's perspective, virtio devices 
> shouldn't be different from either rtl8139, e1000, etc.  It's just 
> another PCI device.
>
> This model makes less sense in the context of stub domains, but if 
> you're running qemu-dm in dom0, you may actually get reasonable 
> performance out of the virtio drivers.
>
> In fact, comparing an HVM domain using virtio with qemu-dm in dom0 
> verses netfront ala PV-on-HVM would make for a very interesting 
> comparison.
>
> And assuming PV-on-HVM isn't in upstream Linux yet (that appears to be 
> the case) and virtio is, it may even be a practical thing to do. 

I have some pvhvm changes sitting here waiting for some testing.  
They're fairly trivial as they completely reuse the existing frontend 
drivers, so its just some stuff to probe for the Xen magic pci device 
and route from the pci interrupt back to event channels.  So I don't 
think there's a lot of code saving either way.

That said, it would be interesting to compare guests using direct pv 
drivers, vs virtio-via-qemu.

    J