vCPU Over allocation is this a potential problem? 2x Physical CPU Sockets in host but VM has 4x Sockets assigned

[BattleNerd]

Hello All!

Was wondering if I could get your help on a matter that i'm not sure is causing issues on VM performance or if its something I should not be concerned about...

All our hosts are Dual Socket 10x Core ESXi 5.5 hosts.

The VM's in question do things like this:

Its using 4x Sockets, and only 1x Core per Socket.... I would have thought VMWare would not allow a allocation like this, instead at most spreading it to 2x Sockets, and 2x Cores per socket, or 1x Socket with 4x Cores.

Can someone let me know if this is a potential issue, as i'm not able to find much referencing this type of mis-configuration.

Thanks!

[RvdNieuwendijk]

It is no problem assigning 4 CPUs to a virtual machine on a host with only two sockets. The CPUs on the virtual machine are assigned to cores on the physical host. The Cores per Socket is introduced to address problems with operating systems that don't support much physical CPUs. See for more information: Setting the number of cores per CPU in a virtual machine (1010184) | VMware KB

[BattleNerd]

But wouldn't this effect NUMA Topology? If you assign multiple Sockets, will this not create multiple NUMA Nodes? From my understanding you want to create as little NUMA Nodes as possible to help keep all processes from switching between cores, each time it hits a different core it loses what was processed in L1/2 Cache... Would this not affect that? Thanks!