On Mon, 2011-12-12 at 13:12 +0000, Michael S. Tsirkin wrote: > On Mon, Dec 12, 2011 at 12:28:27PM +0000, Pawel Moll wrote: > > On Mon, 2011-12-12 at 12:14 +0000, Stefan Hajnoczi wrote: > > > I noticed the virtio-mmio spec has an interrupt status register. On > > > x86 and virtio-pci things are moving towards Message Signalled > > > Interrupts and virtqueues having their own interrupts for better > > > performance and flexibility. Any thoughts on how 1 interrupt per > > > virtqueue works for virtio-mmio? > > > > This could be done by either creating devices with more then one > > interrupt (platform device can take any number of resources) and > > declaring that first queue uses the first one etc. > > We currently support mapping from virtqueues to interrupt > vectors in virtio core. Only virtio pci uses that > but mmio can too. It's better than fixed mapping > IMO as driver can control resources per queue.
I'll keep that in mind. > > > My feeling is that the interrupt details are board-specific and can't > > > be described in virtio-mmio, > > > > It's just the the "design pattern" in the "embedded world" that devices > > usually have one interrupt output, shared between its internal > > functions. And - of course - there is no in-band signalling (like MSI) > > possible - interrupt lines are just "wires" :-) In a boundary case > > scenario we may face a situation when total amount of interrupts for all > > queues may actually exceed amount of interrupt inputs available in the > > interrupt controller... > > > > There may be a half-way solution - one interrupt per device but the > > "active" queue number notified via the interrupt status register (as a > > FIFO) so the driver wouldn't have to enumerate all the queues. > > We could use a queue for this certainly. Hm, yes, I suppose so :-) This would be a "system-level" queue rather than the normal one, but I guess we could do that. > Why do you have so many queues? I assume this a question about the example I gave above? The answer is: I obviously don't :-) This was just to point out that there _may_ be a problem if we wanted to allocate an interrupt per queue. Cheers! Paweł
