Gleb Natapov wrote: > On Mon, Oct 12, 2009 at 09:27:19AM +0200, Jan Kiszka wrote: >> Gleb Natapov wrote: >>> On Mon, Oct 12, 2009 at 09:03:18AM +0200, Jan Kiszka wrote: >>>> Hi, >>>> >>>> I was starring at the IRQ delivery path of assigned devices for a while, >>>> wondering why we have a work queue there. Now, after looking at some >>>> prehistoric versions, I think the reason is that there once was a mutex >>>> involved while we now use RCU. Am I right that we could actually drop >>>> this indirection today? >>>> >>> ioapic/pic path still has mutex. If MSIX is used (like it should) we can >>> drop work queue. >> I see. Wouldn't it be feasible to convert the fast paths of [io]apic to >> spinlocks? >> > 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. Jan
Attachment:
signature.asc
Description: OpenPGP digital signature
