On Thursday 11 March 2010, Avi Kivity wrote: > >> 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. > > Well, we could, but it seems to make things more complicated? A card > with shared memory, and another card with an interrupt interconnect? Yes, I agree that it's more complicated if you have a specific application in mind that needs one of each, and most use cases that want shared memory also need an interrupt mechanism, but it's not always the case: - You could use ext2 with -o xip on a private mapping of a shared host file in order to share the page cache. This does not need any interrupts. - If you have more than two parties sharing the segment, there are different ways to communicate, e.g. always send an interrupt to all others, or have dedicated point-to-point connections. There is also some complexity in trying to cover all possible cases in one driver. I have to say that I also really like the idea of futex over shared memory, which could potentially make this all a lot simpler. I don't know how this would best be implemented on the host though. Arnd -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
