libvirt users - Aug 2011 - CPU Model detection with virsh capabilities

Hello everybody,

I am a new user discovering libvirt with KVM software. During my first 
VM creation, I saw an issue with virsh that I can't understand.

I wanted to emulate another CPU than the classical qemu32 using virsh. 
So I used the virsh capabilites command to detect how is detected my CPU 
host which is an Intel Xeon E5410 and my problem is that this CPU is 
detected only with the cpumodel "pentium3".

But if use the kvm -cpu ? command, it returns me the following 
capabilities :

$ kvm -cpu ?
x86           qemu64
x86           phenom
x86         core2duo
x86            kvm64
x86           qemu32
x86          coreduo
x86              486
x86          pentium
x86         pentium2
x86         pentium3
x86           athlon
x86             n270

Moreover, if i decide to use the pentium3 cpumodel for my KVM VM, the 
CentOS freeze during its loading.

My libvirt and kvm are the following on a Debian Squeeeze :

$ virsh version
Compiled against library: libvir 0.8.3
Using library: libvir 0.8.3
Using API: QEMU 0.8.3
Running hypervisor: QEMU 0.12.5

Does anybody already had the same issue or am I doing anything wrong ?

Thanks for your answers

Regards,
Olivier BONHOMME

Le 02/08/2011 10:51, Olivier BONHOMME a ?crit :
> Hello everybody,
>
> I am a new user discovering libvirt with KVM software. During my first
> VM creation, I saw an issue with virsh that I can't understand.
>
> I wanted to emulate another CPU than the classical qemu32 using virsh.
> So I used the virsh capabilites command to detect how is detected my CPU
> host which is an Intel Xeon E5410 and my problem is that this CPU is
> detected only with the cpumodel "pentium3".
>
> But if use the kvm -cpu ? command, it returns me the following
> capabilities :
>
> $ kvm -cpu ?
> x86 qemu64
> x86 phenom
> x86 core2duo
> x86 kvm64
> x86 qemu32
> x86 coreduo
> x86 486
> x86 pentium
> x86 pentium2
> x86 pentium3
> x86 athlon
> x86 n270
>
> Moreover, if i decide to use the pentium3 cpumodel for my KVM VM, the
> CentOS freeze during its loading.
>
> My libvirt and kvm are the following on a Debian Squeeeze :
>
> $ virsh version
> Compiled against library: libvir 0.8.3
> Using library: libvir 0.8.3
> Using API: QEMU 0.8.3
> Running hypervisor: QEMU 0.12.5
>
> Does anybody already had the same issue or am I doing anything wrong ?
>
Hello again,

I am still locked with that issued about capabilities detection. I tried 
to look on the doc but can't find anything. Does anybody has an entry 
point for that or should it be considered as a bug ?

Thanks again

Regards,
Olivier BONHOMME

Hi,
> I wanted to emulate another CPU than the classical qemu32 using virsh. 
> So I used the virsh capabilites command to detect how is detected my CPU 
> host which is an Intel Xeon E5410 and my problem is that this CPU is 
> detected only with the cpumodel "pentium3".
Libvirt detects host CPU feature-wise. It knows several models and features
they provide (look at /usr/share/libvirt/cpu_map.xml) and selects a model that
implements most of the features of host CPU and there are no features in the
model that host CPU doesn't support. The reason why your CPU is not detected
as more advanced model is most likely that your host CPU doesn't support
some
features included in such models. Can you send us full copy of the <cpu>
element and its children from virsh capabilities?

You can also learn more about configuring guest CPUs with libvirt at
http://berrange.com/posts/2010/02/15/guest-cpu-model-configuration-in-libvirt-with-qemukvm/

Jirka

On Mon, Sep 12, 2011 at 16:33:53 +0200, Olivier BONHOMME
wrote:
> Hello,
> 
> Thanks for your answer. My virsh capabilities is the following :
> 
>      <cpu>
>        <arch>x86_64</arch>
>        <model>pentium3</model>
>        <vendor>Intel</vendor>
>        <topology sockets='1' cores='4'
threads='1'/>
>        <feature name='lahf_lm'/>
>        <feature name='lm'/>
>        <feature name='syscall'/>
>        <feature name='sse4.1'/>
>        <feature name='dca'/>
>        <feature name='xtpr'/>
>        <feature name='cx16'/>
>        <feature name='ssse3'/>
>        <feature name='tm2'/>
>        <feature name='est'/>
>        <feature name='vmx'/>
>        <feature name='ds_cpl'/>
>        <feature name='monitor'/>
>        <feature name='pni'/>
>        <feature name='pbe'/>
>        <feature name='tm'/>
>        <feature name='ht'/>
>        <feature name='ss'/>
>        <feature name='sse2'/>
>        <feature name='acpi'/>
>        <feature name='ds'/>
>        <feature name='clflush'/>
>        <feature name='apic'/>
>      </cpu>
> 
> About what you say, I totally agree. It's just I am very surprised that
> an Intel Xeon E5430 is detected just as a pentium3
That's because your CPU doesn't support nx feature, which is included in
all
models better than pentium3.

Jirka