[Qemu-devel] Re: [PATCH 2/2] virtio: enable msi-x for console+balloon

[Gerd Hoffmann]

On 12/07/09 10:37, Michael S. Tsirkin wrote:
> Sorry, I missed this the first time this was posted, and I see this in
> staging now. Gerd, could you please explain the motivation for this
> patch?
>
> I assumed console/baloon interrupts are not performance critical, so
> would we not be better off using a shared interrupt for these,
> reserving MSI vectors for where performance matters?

The motivation was to move them away from the ioapic, to reduce irq 
sharing of *other* devices which are connected to the ioapic too (i.e. 
usb, e1000, lsi, ...)

I'm aware that these are not performance-critical.  I've even tried to 
use 'vectors=1' because of that.  I expected that would make them use 
MSI-X, but a single IRQ line only.  Didn't work though.  Intentional?

cheers,
  Gerd