Re: [v3 13/26] KVM: Define a new interface kvm_find_dest_vcpu() for VT-d PI

[Paolo Bonzini <pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 19/12/2014 02:30, Wu, Feng wrote:
>>> How this can work well? All subsequent interrupts are delivered to
>>> one vCPU? It shouldn't be the best solution, need more consideration.
>>
>> Well, it's a hardware limitation.  The alternative (which is easy to
>> implement) is to only do PI for single-CPU interrupts.  This should work
>> well for multiqueue NICs (and of course for UP guests :)), so perhaps
>> it's a good idea to only support that as a first attempt.
>>
>> Paolo
> 
> Paolo, what do you mean by "single-CPU interrupts"? Do you mean we don't
> support lowest priority interrupts for PI? But Linux OS uses lowest priority
> for most of the case? If so, we can hardly get benefit from this feature for
> Linux guest OS.

You can post lowest priority interrupts if they are delivered to a
single CPU, in which case they are effectively fixed priority.

If they are broadcast to multiple CPUs, do not post them.

Paolo