Most Proxmox VMs running on louvre and beaubourg do NOT have the NUMA option enabled.
All hypervisor are NUMA machines, with at least 2 different NUMA nodes each.
It is important to enable the Proxmox NUMA option in order to keep virtual CPU cores pinned on real hardware cores and reduce inter-die coherency traffic as much as possible.
The new PCID Proxmox flag also needs to be enabled for all VMs. Without it, Proxmox will not manage Process Context IDentifiers as described in http://linuxeco.com/?p=77
This feature was previously uninteresting but is now critical for performance if some Intel hardware bug (Meltdown, etc...) mitigations are enabled.