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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 12/07/2010 16:52, "Paul Durrant" <paul.durrant@xxxxxxxxxx> wrote:

> Dont' round-robin the callback interrupt.
> 
> Arrange that the event channel callback interrupt always goes to the
> lowest vcpu with a matching local apic. This should, in most cases,
> be VCPU0 (to which all event channels are bound for HVM guests) but
> this cannot be guaranteed.
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> CC: Tim Deegan <tim.deegan@xxxxxxxxxx>

PV drivers should be handling callback on CPU != 0. The example Linux PV
drivers have done that for a very long time indeed. If a workaround is
needed for broken drivers then we need some way to gate it, and we should in
that case force delivery to VCPU0, as we do for some timer interrupts. The
forcing appears to do no harm even if not architecturally correct, and after
all we would be going to these lengths only because delivery to VCPU-not-0
*certainly* doesn't work.

 -- Keir



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