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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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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