Re: [Xen-devel] [PATCH] Dont' round-robin the callback interrupt

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 12/07/2010 17:36, "Paul Durrant" <Paul.Durrant@xxxxxxxxxx> wrote:

>   When we connect our platform driver interrupt, Windows is at liberty to
> allocate vectors on as many or as few cpus as it wishes. I've seen cases where
> it will *not* allocate us a vector on vcpu 0, so we cannot force vcpu 0. Older
> frontends assume vcpu 0, but should function ok if the interrupt does not move
> around.
>   However, that's not the motivation for this patch. In the windows code, we
> only bind event channels to vcpu 0 since we cannot get callback interrupts on
> multiple vcpus simultaneously, since the interrupt is level sensitive. Thus
> round-robining is wasteful in terms of kicking certain data structures between
> caches (assuming a reasonably constant vcpu -> pcpu mapping).

Surely that argument can be made for any interrupt that is set up to
round-robin among multiple CPUs? Obviously in the PV drivers case the
event-channel IRQ is probably the only significant source of round-robin
interrupts. But I don't see that it's special in any other way.

 -- Keir



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