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RE: [Xen-devel] A simple question of CPU emulation in Xen

  • To: "hotmaim" <tinnycloud@xxxxxxxxxxx>
  • From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
  • Date: Mon, 16 May 2011 11:46:26 +1000
  • Cc: xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Sun, 15 May 2011 18:47:01 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcwTH7IHRgI2bkyiRpmd8mrUIXcvnQASv5cg
  • Thread-topic: [Xen-devel] A simple question of CPU emulation in Xen

> 在 2011-5-14,7:41,"James Harper" <james.harper@xxxxxxxxxxxxxxxx> 写道:
> >> Hi :
> >>
> >>     I have a simple question on CPU emulation in Xen.
> >>
> >>    Currently, inside guest, we can see that the CPU information
> > incluing
> >> types and frequency is exactly
> >> same as physical CPU. Is it possible for Xen(or qemu) to emulate a
> > different
> >> type of CPU. That is inside
> >> guest, we see a different CPU types?
> >>
> >>    If it is possible, could someone elighten me where to start.
> >>
> >
> > Do you want to emulate a completely different platform (eg PPC / alpha /
> > Sparc) or just pretend the cpu is a slightly different flavours (eg
> > running a late model Xeon CPU but emulate a P2)?
> >
> Thanks, exactly what I want.
> since cpus are shared along All VMs, so In guest, youn will get lower score if
> we make tests
> with Xeon.  While higher score is it is pretend to be P2.
> > In a lot of cases you can do the latter by changing some CPUID values in
> > the DomU config to mask the CPU features so the guest thinks it is
> > running on an older model.
> Could i have the configuration u refer to? In hvm file?
> Thanks

I did something like this to give my DomU the lowest common feature set between 
my AMD and Intel based servers for live migration:

cpuid = [ '0:eax=0x3,ebx=0x0,ecx=0x0,edx=0x0',

But I haven't tried it in a while so I can't tell if it still works as it 
should. I do know that Silverlight won't install with the above because it 
requires some feature that I've masked out.

There are some other examples in the example configs I think.


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