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[Xen-devel] Re: [Patch] Add VMX memory-mapped Local APIC access optimiza

To: "Cui, Dexuan" <dexuan.cui@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [Patch] Add VMX memory-mapped Local APIC access optimization
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Thu, 22 Mar 2007 08:37:10 +0000
Cc: "Mallick, Asit K" <asit.k.mallick@xxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
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Is there documentation describing this VMX extension? And what about
availability of silicon?

 -- Keir

On 21/3/07 02:08, "Cui, Dexuan" <dexuan.cui@xxxxxxxxx> wrote:

> Some operating systems access the local APIC TPR very frequently, and we
> handle that using software-based local APIC virtualization in Xen today.
> Such virtualization incurs a number of VM exits from the memory-access
> instructions against the APIC page in the guest.
> The attached patch enables the TPR shadow feature that provides APIC TPR
> virtualization in hardware. Our tests indicate it can significantly
> boost the performance of such guests including 32-bit Windows XP/2003.
> Moreover, with the patch, local APIC accesses other than TPR in guests
> are intercepted directly as APIC_ACCESS VM exits rather than PAGE_FAULT
> VM exits; this can lower the emulation cost of such accesses.
> Signed-off-by: Dexuan Cui <dexuan.cui@xxxxxxxxx>

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