Re: irq_guest_eoi_timer interaction with MSI

["Jan Beulich" <jbeulich@novell.com>]

>>> Keir Fraser <keir.fraser@eu.citrix.com> 13.11.08 16:06 >>>
>On 13/11/08 14:53, "Jan Beulich" <jbeulich@novell.com> wrote:
>
>> Avoiding the EOI query is certainly a secondary issue. What I was asking
>> was rather a means for the guest to know whether Xen started that EOI
>> timer, so that it could indicate to Xen to terminate it and unmask the
>> respective IRQ. This shouldn't require always using PHYSDEVOP_eoi, and
>> from an abstract point of view also would belong there, but rather in
>> unmask_evtchn(). Since it would be an obvious thing that if you unmask
>> an event channel, you also want the underlying PIRQ unmasked, this
>> could be a compatible addition to the existing EVTCHNOP_unmask. The
>> only thing missing is a way for the guest to know when to actually use
>> the hypercall based unmasking - that's what I wanted to add a vector
>> for.
>
>PHYSDEVOP_eoi and unmask happen at the same time for pirqs. The fact that we
>only need this new mechanism for pirqs, and that we already have a gated
>hypercall for pirq eoi (and can gate it further if need be) is an argument
>for hanging this off PHYSDEVOP_eoi imo.

But then there'd be a hypercall for each MSI instance, most of the time
without any real need. With a high interrupt rate I'm afraid this does
matter.

Jan