On Mon, Oct 12, 2009 at 11:07:28AM +0200, Jan Kiszka wrote: > Avi Kivity wrote: > > On 10/12/2009 09:50 AM, Jan Kiszka wrote: > >>> Apic is lockless. For ioapic/pic I used spinlocks initially, but Avi > >>> prefers mutexes. Theoretically it is possible to make them lockless, > >>> but code will be complex and eventually more slow, since more then two > >>> atomic operation will be used on irq injection path. > >>> > >> Well, lockless is another thing. > >> > >> But also converting to spinlocks would indeed add some overhead: > >> irqsave/restore. But I wonder if this isn't worth it, at least when > >> looking at the (supposed to be fast) device passthrough scenario which > >> would be simpler and faster. > >> > > > > I'm worried about disabling irqs for non-device-assignment cases. It > > would be more palatable if ioapic was completely O(1) (there are some > > per-vcpu loops in there, shouldn't be too bad for 16 vcpus, but we want > > to scale). > > Yeah, what a pity. That's likely not solvable in a generic way, given > that the guest finally decided how many VCPUs may listen to a line. > > OK, but dropping interrupt_work from the MSI path is still worthwhile, > and probably more future-proof anyway. Seems appropriate to convert the process context work to threaded interrupt (instead of workqueue). That should help latency. -- 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
