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[Xen-devel] Re: [PATCH] libxc: remove CPUID core information mangling

To: Andre Przywara <andre.przywara@xxxxxxx>, Nitin Kamble <nitin.a.kamble@xxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] libxc: remove CPUID core information mangling
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 25 Aug 2010 13:42:17 +0100
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 25/08/2010 13:04, "Andre Przywara" <andre.przywara@xxxxxxx> wrote:

> Hi,
> c/s 18560:782599274bf9ae8857c55856c9c7fdf082967808 introduced CPUID
> mangling resulting in a doubled number of cores/processor exposed to the
> guest. According to comments in this patch the rationale behind this is
> to match the APIC numbering used by Xen.
> In my understanding the CPUID leafs dealing with number of cores always
> talk about logical numbers and not APIC IDs. So we don't need to adjust
> the CPUID readout to match the APIC ID enumeration scheme.
> If there were any serious reasons resulting in the old patch I'd love to
> hear them.
> The attached patch fixes this and solves an issue I saw with certain
> NUMA guest configurations.

I think you shouldn't change handling of 80000008:ECX[15:12] since that does
explicitly refer to APIC ID arrangement. The rest of your changes could be
correct as far as I can tell from the reference manuals.

The intent by the way was to pass through host cores-per-package info so
that software licenses based on #packages would operate correctly in a
virtualised environment. It's pretty hacky though indeed.

 -- Keir

> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>

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