On Thursday 11 March 2010, Avi Kivity wrote:
A totally different option that avoids this whole problem would
be to separate the signalling from the shared memory, making the
PCI shared memory device a trivial device with a single memory BAR,
and using something a higher-level concept like a virtio based
serial line for the actual signalling.
That would be much slower. The current scheme allows for an
ioeventfd/irqfd short circuit which allows one guest to interrupt
another without involving their qemus at all.
Yes, the serial line approach would be much slower, but my point
was that we can do signaling over "something else", which could
well be something building on irqfd.