Weird CPU separation question for Ryzen

[nagi]

Hi,

 

weird question: is there a way for the KVM layer to make it seem to a Windows VM as if the physically single CPU was actually 2 roughly half-sized physical CPUs?

So basically take a single 8-core CPU, (take 1 off for the virtualization layer,) and pass what appears to be a separate 3 and 4 core CPU to the Windows 7 Pro VM?

 

The question arose while I was erading up on Ryzen, because the current R7 CPUs are basically 2 separate CPUs (each called a CCX, separate cache, same system memory) on the same PCB.

[scorcho99]

I've wondered this question myself. I know esxi you can (optionally) flag specific cores to be used, and I think the concept of cpu pinning used with KVM should be able to do this here as well. In theory if you only need a quad in the VM you can eliminate the CCX crosstalk within that VM at least.

[nagi]

Yeah, I know it is possible to only assign e.g.: the second to a VM, my question is more about assigning the rest of the cores of the other CCX as a seemingly separate physical CPU, as the hypervisor certainly does not need  a whole 4-core CCX, and the extra cores - if utilized correctly - would certainly be welcome.

[1812]

What I think you are asking about is Cgroups: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Resource_Management_Guide/ch01.html

 

and https://libvirt.org/cgroups.html

 

This is the closest I've come to finding anything about it on unRaid: