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.
--
Gleb.
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