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

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Message-ID: <A9667DDFB95DB7438FA9D7D576C3D87E0AC048A2@SHSMSX104.ccr.corp.intel.com>
Date:	Thu, 18 Dec 2014 14:49:22 +0000
From:	"Zhang, Yang Z" <yang.z.zhang@...el.com>
To:	"Wu, Feng" <feng.wu@...el.com>,
	"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>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"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>
CC:	"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

Feng Wu wrote on 2014-12-12:
> This patch defines a new interface kvm_find_dest_vcpu for
> VT-d PI, which can returns the destination vCPU of the
> interrupt for guests.
> 
> Since VT-d PI cannot handle broadcast/multicast interrupt,
> Here we only handle Fixed and Lowest priority interrupts.
> 
> The current method of handling guest lowest priority interrtups
> is to use a counter 'apic_arb_prio' for each vCPU, we choose the
> vCPU with smallest 'apic_arb_prio' and then increase it by 1.
> However, for VT-d PI, we cannot re-use this, since we no longer
> have control to 'apic_arb_prio' with posted interrupt direct
> delivery by Hardware.
> 
> Here, we introduce a similar way with 'apic_arb_prio' to handle guest
> lowest priority interrtups when VT-d PI is used. Here is the ideas: -
> Each vCPU has a counter 'round_robin_counter'. - When guests sets an
> interrupts to lowest priority, we choose the vCPU with smallest
> 'round_robin_counter' as the destination, then increase it.
 
How this can work well? All subsequent interrupts are delivered to one vCPU? It shouldn't be the best solution, need more consideration. Also, I think you should take the apic_arb_prio into consider since the priority is for the whole vCPU not for one interrupt.

Best regards,
Yang


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