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

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Date:	Thu, 13 Nov 2014 01:30:54 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	"Zhang, Yang Z" <yang.z.zhang@...el.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Alex Williamson <alex.williamson@...hat.com>
CC:	"gleb@...nel.org" <gleb@...nel.org>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"joro@...tes.org" <joro@...tes.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [PATCH 05/13] KVM: Update IRTE according to guest interrupt
 configuration changes



> -----Original Message-----
> From: Zhang, Yang Z
> Sent: Thursday, November 13, 2014 9:21 AM
> To: Wu, Feng; Paolo Bonzini; Alex Williamson
> Cc: gleb@...nel.org; dwmw2@...radead.org; joro@...tes.org;
> tglx@...utronix.de; mingo@...hat.com; hpa@...or.com; x86@...nel.org;
> kvm@...r.kernel.org; iommu@...ts.linux-foundation.org;
> linux-kernel@...r.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@...r.kernel.org wrote on 2014-11-12:
> >> kvm@...r.kernel.org; iommu@...ts.linux-foundation.org;
> >> linux-kernel@...r.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
> >> --
> >> To unsubscribe from this list: send the line "unsubscribe kvm" in the
> >> body of a message to majordomo@...r.kernel.org More majordomo info at
> >> http://vger.kernel.org/majordomo-info.html
> 
> 
> Best regards,
> Yang
>