linux-kernel - RE: [v3 13/26] KVM: Define a new interface kvm_find_dest

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Date:	Tue, 13 Jan 2015 00:27:59 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Kr?má? <rkrcmar@...hat.com>
CC:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"gleb@...nel.org" <gleb@...nel.org>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"joro@...tes.org" <joro@...tes.org>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"jiang.liu@...ux.intel.com" <jiang.liu@...ux.intel.com>,
	"eric.auger@...aro.org" <eric.auger@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [v3 13/26] KVM: Define a new interface kvm_find_dest_vcpu() for
 VT-d PI



> -----Original Message-----
> From: Paolo Bonzini [mailto:pbonzini@...hat.com]
> Sent: Friday, January 09, 2015 10:56 PM
> To: Radim Krčmář; Wu, Feng
> Cc: tglx@...utronix.de; mingo@...hat.com; hpa@...or.com; x86@...nel.org;
> gleb@...nel.org; dwmw2@...radead.org; joro@...tes.org;
> alex.williamson@...hat.com; jiang.liu@...ux.intel.com; eric.auger@...aro.org;
> linux-kernel@...r.kernel.org; iommu@...ts.linux-foundation.org;
> kvm@...r.kernel.org
> Subject: Re: [v3 13/26] KVM: Define a new interface kvm_find_dest_vcpu() for
> VT-d PI
> 
> 
> 
> On 09/01/2015 15:54, Radim Krčmář wrote:
> > There are two points relevant to this patch in new KVM's implementation,
> > ("KVM: x86: amend APIC lowest priority arbitration",
> >  https://lkml.org/lkml/2015/1/9/362)
> >
> > 1) lowest priority depends on TPR
> > 2) there is no need for balancing
> >
> > (1) has to be considered with PI as well.
> 
> The chipset doesn't support it. :(
> 
> > I kept (2) to avoid whining from people building on that behaviour, but
> > lowest priority backed by PI could be transparent without it.
> >
> > Patch below removes the balancing, but I am not sure this is a price we
> > allowed ourselves to pay ... what are your opinions?
> 
> I wouldn't mind, but it requires a lot of benchmarking.

In fact, the real hardware may do lowest priority in round robin way, the new
hardware even doesn't consider the TPR for lowest priority interrupts delivery.

As discussed with Paolo before, I will submit a patch to support lowest priority for PI
after this series is merged.

Thanks,
Feng

> 
> Paolo