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Re: [libvirt] inquiry, get native capabilities of the host



Hi,

On Thu, May 12, 2011 at 15:39:44 -0700, Dong-In David Kang wrote:
>  I'm interested in getting native capabilities of host CPU using libvirt.
> I've looked at .../src/cpu/cpu_map.xml.
> And it does describe native capabilities of host CPU very well. 
> But, libvirt always returns a subset of the native capabilities which is far different from the feature lists in the xml file.
> (I'm testing with <model name='Westmere'>.)
> The sponsor of my project is interested is high-performance computing. 
> And knowing native feature of the host CPU that can also be available to a virtual machine is very important for performance reason.
> 
>  I couldn't find how to get the native features of the host that is described in .../src/cpu/cpu_map.xml.
> Is there a way or libvirt API to get the native capabilities of host CPU that is well described in .../src/cpu/cpu_map.xml?

I'm not sure I totally understand what you are looking for. Is the issue you
have that virsh capabilities tells you something like this:

  <cpu>
    <arch>x86_64</arch>
    <model>Westmere</model>
    <vendor>Intel</vendor>
    <topology sockets='1' cores='2' threads='2'/>
    <feature name='rdtscp'/>
    <feature name='xtpr'/>
    <feature name='tm2'/>
    <feature name='est'/>
    <feature name='vmx'/>
    <feature name='ds_cpl'/>
    <feature name='monitor'/>
    <feature name='pbe'/>
    <feature name='tm'/>
    <feature name='ht'/>
    <feature name='ss'/>
    <feature name='acpi'/>
    <feature name='ds'/>
    <feature name='vme'/>
  </cpu>

while in cpu_map.xml mentions much more features for Westmere model? If so,
than the answer is quite simple. The thing is that the CPU description is
additive, that is the above XML snippet says that host CPU supports all
features that are defined by Westmere CPU model in cpu_map.xml *plus* the
features that are explicitly listed in the above <cpu> element. So if you
expand the model, you get a full list of features supported by the host CPU:

  <!-- from Nehalem which Westmere is derived from -->
  <feature name='sse2'/>
  <feature name='sse'/>
  <feature name='fxsr'/>
  <feature name='mmx'/>
  <feature name='pat'/>
  <feature name='cmov'/>
  <feature name='pge'/>
  <feature name='sep'/>
  <feature name='apic'/>
  <feature name='cx8'/>
  <feature name='mce'/>
  <feature name='pae'/>
  <feature name='msr'/>
  <feature name='tsc'/>
  <feature name='pse'/>
  <feature name='de'/>
  <feature name='fpu'/>
  <feature name='mtrr'/>
  <feature name='clflush'/>
  <feature name='mca'/>
  <feature name='pse36'/>
  <feature name='pni'/>
  <feature name='cx16'/>
  <feature name='ssse3'/>
  <feature name='sse4.1'/>
  <feature name='sse4.2'/>
  <feature name='popcnt'/>
  <feature name='lm'/>
  <feature name='syscall'/>
  <feature name='nx'/>
  <feature name='lahf_lm'/>

  <!-- from Westmere -->
  <feature name='aes'/>

  <!-- explicitly listed -->
  <feature name='rdtscp'/>
  <feature name='xtpr'/>
  <feature name='tm2'/>
  <feature name='est'/>
  <feature name='vmx'/>
  <feature name='ds_cpl'/>
  <feature name='monitor'/>
  <feature name='pbe'/>
  <feature name='tm'/>
  <feature name='ht'/>
  <feature name='ss'/>
  <feature name='acpi'/>
  <feature name='ds'/>
  <feature name='vme'/>

Jirka


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