Sockets vs Cores vs vCPUs

[Muhammad.Hesham]

Hello,

I'm a little bit confused when it comes to the terms Sockets, Cores, vCPUs in Proxmox. I checked older forums but they only helped confuse me more xD

So as far as I understand Socket defines the number of processors I have (For example: 2x AMD Ryzen™ 5 PRO 3600 means I have 2 sockets), Cores defines the number of threads not the number of physical cores (so in Proxmox I can assign up to 12 cores to a VM not just 6 in case of 1x AMD Ryzen™ 5 PRO 3600) and vCPU is the result of the multiplication of the Sockets by the Cores (For example: If I assign 2 sockets and 2 c.

Did I get that right or am I misunderstanding something?

 

[waltar]

Quiet ok but as sockets for virtual machines even use virtual sockets performance is always better if you select at creation time just 1 socket and a number of cores to your wish (but not to much as it doesn't is really useful and better for the virt host to serve the vm's, same for memory).

 

[nashbrydges]

My typical approach is to always set sockets = 1 and Cores = X (whatever I want but always less than or equal to the core count of 1 CPU. If you schedule more resources than that single CPU, you take a hit on performance because of the NUMA scheduling between the CPUs. Similarly for RAM, it will be managed by both CPUs so 50% for 1 CPU and 50% for the other and assign VM RAM accordingly (again, I try to avoid the performance hit for cross CPU scheduling). I let the CPU scheduling take care of the rest.