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

[Wu, Feng]

> -----Original Message-----
> From: kvm-owner@xxxxxxxxxxxxxxx [mailto:kvm-owner@xxxxxxxxxxxxxxx] On
> Behalf Of Paolo Bonzini
> Sent: Wednesday, November 12, 2014 5:56 PM
> To: Wu, Feng; Zhang, Yang Z; Alex Williamson
> Cc: gleb@xxxxxxxxxx; dwmw2@xxxxxxxxxxxxx; joro@xxxxxxxxxx;
> tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; hpa@xxxxxxxxx; x86@xxxxxxxxxx;
> 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.

Thanks,
Feng

> 
> Paolo
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Attachment: VT-d PI Performance on KVM.pdf
Description: VT-d PI Performance on KVM.pdf