Gleb Natapov wrote: > On Mon, Oct 12, 2009 at 10:16:56AM +0200, 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. >>>> >>> Avi's point in favor of mutex is: they are as fast as spinlocks when >>> congested and allows preemption when held. >> ...but require scheduler activity in case of dev-passthrough, which is >> surely playing in a different league. >> > I'd rather remove dev-passthrough completely than continue adding hack upon hack > upon hack to make is some times kinda sorta work :) Hmm, is this code not needed for the VT-d & Co. case? Or what is the alternative? Jan
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