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

Wu, Feng
2014-11-13T01:32:45Z

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> -----Original Message-----
> From: Zhang, Yang Z
> Sent: Thursday, November 13, 2014 9:21 AM
> To: Wu, Feng; Paolo Bonzini; Alex Williamson
> Cc: gleb@kernel.org; dwmw2@infradead.org; joro@8bytes.org;
> tglx@linutronix.de; mingo@redhat.com; hpa@zytor.com; x86@kernel.org;
> 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
>
> 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).

Yes, this data is VT-d PI vs Non VT-d PI. The CPU side APICv mechanism (including CPU side Posted-Interrtups) is enabled.

Thanks,
Feng

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

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