Re: [Xen-users] 'lowest common denominator' cpuid feature set

[Keith Coleman <list.keith@xxxxxxxxxxx>]

On Tue, Nov 17, 2009 at 5:56 PM, James Harper
<james.harper@xxxxxxxxxxxxxxxx> wrote:
> I want to be able to test live migration... I have an intel box and an
> amd box, so live migration between them won't 'just work'. From what
> I've read though, I should be able to use cpuid to turn off all the cpu
> features which might be different between them. Is this do-able? I'm
> willing to accept any resulting loss of performance etc.
>

James,

You can use localhost as the migration target to eliminate CPU and
shared storage requirements.

It's possible to mask cpu features resulting in a generic vcpu that
should run on intel or amd. The following excerpt is taken from the
xen sample config file xmexample.hvm:

>From the xmexample.hvm
#  Downgrade the cpuid to make a better compatibility for migration :
# Look like a generic 686 :
# cpuid = [ '0:eax=0x3,ebx=0x0,ecx=0x0,edx=0x0',
#           '1:eax=0x06b1,
#              ecx=xxxxxxxxxxx0000xx00xxx0000000xx0,
#              edx=xxx00000xxxxxxx0xxxxxxxxx0xxxxxx',
#           '4:eax=0x3,ebx=0x0,ecx=0x0,edx=0x0',
#  '0x80000000:eax=0x3,ebx=0x0,ecx=0x0,edx=0x0']
#  with the highest leaf
#  - CPUID.0[EAX] : Set the highest leaf
#  - CPUID.1[EAX] : 686
#  - CPUID.1[ECX] : Mask some features
#  - CPUID.1[EDX] : Mask some features
#  - CPUID.4 : Reply like the highest leaf, in our case CPUID.3
#  - CPUID.0x80000000 : No extension we are on a Pentium III, reply like the
#  highest leaf (CPUID.3).



Keith Coleman

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