Re: assign-dev: Purpose of interrupt_work

[Gleb Natapov <gleb@redhat.com>]

On Mon, Oct 12, 2009 at 10:39:09AM +0200, 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).
> 
We can change it to hash for directed irqs (still not O(1)), but for
broadcast irq the loop will be required.

--
			Gleb.