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

[Paolo Bonzini]

On 18/12/2014 15:49, Zhang, Yang Z wrote:
>>> Here, we introduce a similar way with 'apic_arb_prio' to handle
>>> guest lowest priority interrtups when VT-d PI is used. Here is
>>> the ideas: - Each vCPU has a counter 'round_robin_counter'. -
>>> When guests sets an interrupts to lowest priority, we choose the
>>> vCPU with smallest 'round_robin_counter' as the destination, then
>>> increase it.
> 
> 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

> Also, I think you should take the apic_arb_prio into consider since
> the priority is for the whole vCPU not for one interrupt.
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