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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 12/07/2010 18:17, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:

>>   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.

Further, the correct semantics for LowestPrio delivery was implemented by
Juergen Gross at Fujitsu for a reason. Cc'ing him. I suspect he will say
that relaxing the delivery semantics will cause something he cares about to
break.

 -- Keir



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