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

[Zhang, Yang Z]

Wu, Feng wrote on 2014-11-13:
> 
> 
> kvm-owner@xxxxxxxxxxxxxxx wrote on 2014-11-12:
>> kvm@xxxxxxxxxxxxxxx; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; 
>> linux-kernel@xxxxxxxxxxxxxxx
>> 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