Re: [Xen-users] HVM falls back to qemu emulation while VMX is enabled (Xen 3.1)

[Pim van Riezen <pi+lists@xxxxxxxxxxxx>]

On Oct 7, 2008, at 17:15 , Andrew Lyon wrote:

> On Tue, Oct 7, 2008 at 3:31 PM, Pim van Riezen <pi 
> +lists@xxxxxxxxxxxx> wrote:
> > On Oct 7, 2008, at 16:20 , Andrew Lyon wrote:
> >
> > > > I've briefly tried xen/xend 3.2 on the machine. If I used the
> > > > /boot/xen.gz-3.2 as the hypervisor, /proc/cpuinfo would stop  
> > > > listing vmx
> > > > among the capabilities. Going back to the RedHat version of  
> > > > xen-3.1 and
> > > > xend-3.0, I get them back:
> > > Not that it helps with your problem, but not seeing vmx in
> > > /proc/cpuinfo is normal for newer versions of Xen, after all Linux
> > > cannot use the vmx feature as it is already being used by the Xen
> > > hypervisor, so it is logical that the feature is no longer listed.
> > At least it's good to know there is nothing inherently wrong with  
> > that
> > xen-3.2 hypervisor then, although the end result on that hypervisor  
> > was the
> > same (cpu of the guest got fully emulated, slower than booting GEOS  
> > on my
> > C64).
> >
> > Pi
> I don't think that is possible, afaik Xen can only run Windows through
> HVM, there was a modified build of windows that was paravirtualized
> but it was never released to the public, only some Xen developers at
> cambridge university had access, so you are using vmx/hvm and your
> problem is not that the cpu is being fully emulated, it is something
> else!
Ok, in that case let me restate my question without preconceptions  
about its cause:
I start the guest, it starts eating 100% cpu in xm top. It takes  
forever booting and logging me into a desktop. It's the effect of  
running on a severely underpowered CPU of a 386 class or lower. In  
xentop, Domain-0 also seems to be taking up a lot of cpu, around 70%.  
Running top in Dom0 shows qemu-md taking up that cpu-time.
If qemu-md were running a bochs-style emulation, that is what I'd  
expect to see.
If I start the same guest on the Xeon 5150 machine, I see 0% CPU usage  
in Domain-0 and the guest boots like lightning.
Cheers,
Pi


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