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. Jan
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