[pve-devel] [PATCH] add win81 ostype and use qemu64 cpumodel if kvm64 is defined

Alexandre DERUMIER aderumier at odiso.com
Wed Nov 27 08:51:22 CET 2013


in libvirt: src/cpu/cpu_map.xml

they a are a cpu list definition, with standard cpu but also custom cpu

...
    <model name='cpu64-rhel6'>
      <model name='cpu64-rhel5'/>
      <feature name='cx16'/>
      <feature name='lahf_lm'/>
    </model>

--> this one is the default used by rhev, they have enabled the lahf_lm flag
    https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Host_Configuration_and_Guest_Installation_Guide/ch03s02.html

    Rhev don't support qemu64 or kvm64 cpu type, but only their own custom cpu definition



   another interesting note, why kvm64 model have less flags than qemu64:

    <model name='qemu64'>
      <model name='kvm64'/>
      <!-- These are supported only by TCG.  KVM supports them only if the
           host does.  So we leave them out:

           <feature name='popcnt'/>
           <feature name='lahf_lm'/>
           <feature name='sse4a'/>
           <feature name='abm'/>
      -->
      <feature name='svm'/>
    </model>

according to :
http://en.wikipedia.org/wiki/SSE4

sse4a :  These instructions are not available in Intel processors.
popcnt: Intel implements POPCNT beginning with the Nehalem microarchitecture.AMD calls this pair of instructions Advanced Bit Manipulation (ABM).
abm: same thatn popcnt, but amd only

so theses 3flags make sense

but lahf_lm is supported by amd and intel since a long time.
Don't known why they remove it


----- Mail original ----- 

De: "Alexandre DERUMIER" <aderumier at odiso.com> 
À: "Dietmar Maurer" <dietmar at proxmox.com> 
Cc: pve-devel at pve.proxmox.com 
Envoyé: Mercredi 27 Novembre 2013 08:22:39 
Objet: Re: [pve-devel] [PATCH] add win81 ostype and use qemu64 cpumodel if kvm64 is defined 

>>How does libvirt handle that? 

AFAIK, libvirt don't choose for you the best cpu type for a specific os. 

But maybe ovirt,rhev,openstack are doing it in their code. 
I'll try to have a look at them. 


----- Mail original ----- 

De: "Dietmar Maurer" <dietmar at proxmox.com> 
À: "Alexandre Derumier" <aderumier at odiso.com>, pve-devel at pve.proxmox.com 
Envoyé: Mercredi 27 Novembre 2013 06:54:18 
Objet: RE: [pve-devel] [PATCH] add win81 ostype and use qemu64 cpumodel if kvm64 is defined 

How does libvirt handle that? 

> see 
> http://forum.proxmox.com/threads/16206-Windows-Server-2012-R2-and- 
> 0x0000005D-Error 
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