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

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Date:	Fri, 09 Jan 2015 15:56:00 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>,
	Feng Wu <feng.wu@...el.com>
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.

Paolo
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