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    SubjectRE: [v3 13/26] KVM: Define a new interface kvm_find_dest_vcpu() for VT-d PI
    Date
    Wu, Feng wrote on 2014-12-19:
    >
    >
    > Paolo Bonzini wrote on 2014-12-19:
    >> jiang.liu@linux.intel.com
    >> Cc: eric.auger@linaro.org; linux-kernel@vger.kernel.org;
    >> iommu@lists.linux-foundation.org; kvm@vger.kernel.org
    >> Subject: Re: [v3 13/26] KVM: Define a new interface
    >> kvm_find_dest_vcpu() for VT-d PI
    >>
    >>
    >>
    >> 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
    >
    > Paolo, what do you mean by "single-CPU interrupts"? Do you mean we

    It should be same idea as I mentioned on another thread: deliver the interrupt to a single CPU(maybe the first matched VCPU?)

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


    Best regards,
    Yang




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