Performance-cores vs Efficient-cores

[Fathi]

Hi,
The latest intel i7 processors seem to be capped at 8 Performance-cores while paying more money gives you more Efficient-cores.
1) Should we ? I mean, is there really any benefit for PVE to increase the number of Efficient-cores ? I feel that price could go exponentially while performance go logarithmiccaly when following the latest i7 CPUs.
2) How does PVE handle this dissimetry of cores (ones with HT and the others without) ?
TIA.
Fathi B.N.

 

[_gabriel]

currently you need to "pin" P cores or E cores to VMs as you need.
Myself, I disable E cores from BIOS.
btw, Server grade CPU do not have E cores.

 

[VictorSTS]

Support for Intel P/E cores was introduced in Linux kernel aroud 5.18 AFAIR with different improvements being applied on recent kernels too via Intel thread director. Not fully sure about which features are included in Proxmox kernel.

You can always use Proxmox CPU Affinity feature to pin the QEMU cpu threads to given cores, so you can decide which VM will be run on which core(s).

 

[Fathi]

So one could reserve the E cores for PVE itself and provision the P cores to VMs and containers.
By the way, what is the ration, when having enough cpus and a lot of vms, of the cores to reserve to pve and the ones to provision to vms ? I read somewhere that pve needs 4Gb ram and 4 cpus for itself; is this independent of the number of vms/containers running or does it increase with the resources allocated to vms ?

 

[VictorSTS]

Unless your VMs do really load the host too much, there's no need to "reserve" CPUs for the host itself. The host does need some CPU and how much depends on many factors: if theres cluster, type of storage(s), how many data and how often backups are run, other software running on host like VPN, monitoring, etc, etc.

The kernel should be smart enough to schedule all tasks on it's own. I suggest that you simply try without messing around with cpu pinning for neither VMs or the host, run benchmarks, try your workloads, etc, as many tasks can be run perfectly fine on an E core.