[ovirt-users] host-passthrough or pcid enable for Westmere and SandyBridge

[Florian Schmid]

Hi,

are there any news on this?

I tried to change /usr/share/libvirt/cpu_map.xml manually and added pcid flag to SandyBridge CPU and restarted HW node, but on VM, nothing changed.
I found the xml file for this VM and I found a strange content:
In /var/run/libvirt/qemu/, there are the XML files of the running VMs ->
...
    <cpu mode='custom' match='exact' check='full'>
      <model fallback='forbid'>SandyBridge</model>
      <topology sockets='16' cores='1' threads='1'/>
      <feature policy='require' name='vmx'/>
      <feature policy='require' name='vme'/>
      <feature policy='disable' name='pcid'/>
      <feature policy='require' name='hypervisor'/>
      <feature policy='require' name='arat'/>
      <feature policy='require' name='xsaveopt'/>
...
-> feature policy='disable' name='pcid'

It was indeed added to XML file, but it looks like it is somehow disabled.

I actually don't know, how to enable it.

On hosts, where cpu_map.xml is not changed, this entry is not there.

We are running version 4.1.7

BR Florian

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----- Ursprüngliche Mail -----
Von: "Eduardo Mayoral" <emayoral at arsys.es>
An: "users" <users at ovirt.org>
Gesendet: Donnerstag, 11. Januar 2018 07:56:56
Betreff: [ovirt-users] host-passthrough or pcid enable for Westmere and	SandyBridge

Hi,

    With the meltdown patches, now it is specially beneficial to have
the pcid feature in the virtual CPUs. See:

https://groups.google.com/forum/#!topic/mechanical-sympathy/L9mHTbeQLNU

    The PCID feature is available in physical "Westmere" (Release date
circa 2010) or newer CPUs.

    However, in libvirt the pcid feature is only avalilable for virtual
CPUs Haswell (Release date circa 2013) or newer. The recomendation is
using Haswell, Broadwell or Skylake based model or host passthrough.
Now, I think "host passthrough" is not an option for oVirt for good
reason so this leaves Haswell, Broadwell or Skylake as options.

    Is it possible to edit /usr/share/libvirt/cpu_map.xml on the compute
nodes to add the pcid feature to the virtual CPU models between Westmere
and Haswell (that would be Westmere and SandyBridge)? Is anyone aware if
something like this is being considered by the libvirt developers?
Actually understanding the implications or doing so is way beyond my
skill level.

    By now you may have guessed that my oVirt clusters use physical
Westmere and SandyBridge CPUs :-/

    Thanks in advance for your help!

-- 

Eduardo Mayoral Jimeno (emayoral at arsys.es)
Administrador de sistemas. Departamento de Plataformas. Arsys internet.
+34 941 620 145 ext. 5153

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