RE: [PATCH 05/13] KVM: Update IRTE according to guest interrupt configuration changes

Zhang, Yang Z
2014-11-13T01:21:58Z

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Wu, Feng wrote on 2014-11-13:
>
>
> kvm-owner@vger.kernel.org wrote on 2014-11-12:
>> kvm@vger.kernel.org; iommu@lists.linux-foundation.org;
>> linux-kernel@vger.kernel.org
>> Subject: Re: [PATCH 05/13] KVM: Update IRTE according to guest
>> interrupt configuration changes
>>
>>
>>
>> On 12/11/2014 10:19, Wu, Feng wrote:
>>>> You can certainly backport these patches to distros that do not
>>>> have VFIO. But upstream we should work on VFIO first. VFIO has
>>>> feature parity with legacy device assignment, and adding a new
>>>> feature that is not in VFIO would be a bad idea.
>>>>
>>>> By the way, do you have benchmark results for it? We have not been
>>>> able to see any performance improvement for APICv on e.g. netperf.
>>>
>>> Do you mean benchmark results for APICv itself or VT-d Posted-Interrtups?
>>
>> Especially for VT-d posted interrupts---but it'd be great to know
>> which workloads see the biggest speedup from APICv.
>
> We have some draft performance data internally, please see the
> attached. For VT-d PI, I think we can get the biggest performance gain
> if the VCPU is running in non-root mode for most of the time (not in
> HLT state), since external interrupt from assigned devices will be delivered by guest directly in this case.
> That means we can run some cpu intensive workload in the guests.

Have you check that the CPU side posted interrupt is taking effect in w/o VT-D PI case? Per my understanding, the performance gap should be so large if you use CPU side posted interrupt. This data more like the VT-d PI vs non PI(both VT-d and CPU).

>
> Thanks,
> Feng
>
>>
>> Paolo
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Best regards,
Yang

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