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

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Message-ID: <A9667DDFB95DB7438FA9D7D576C3D87E0ABE5A68@SHSMSX104.ccr.corp.intel.com>
Date:	Thu, 13 Nov 2014 01:21:16 +0000
From:	"Zhang, Yang Z" <yang.z.zhang@...el.com>
To:	"Wu, Feng" <feng.wu@...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>
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).

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