Unable to increase number of Processors from 32 CPUs although host has 80 cores.

[nikhil_parihar]

I've updated the virtualBox and it's the latest one (6.1.16).
There are 40 physical cores (80 by hyperthreading) on host machine but in the "settings" section of a VM (oracle linux 7.3) there's maximum limit of only 32 CPUs and I want to assign 44 CPUs to the VM.
so why it's not showing the total number of processors available (40 or 80)?? is there any limitation on number of processors Vbox can assign to any VM??

[mpack]

First, threads are not cores. A core is a piece of discrete silicon, not just an additional instruction pipeline. You have 40 cores.

Second, yes 32 cores is the VirtualBox limit, as it clearly states in the manual:

• Processor(s): Sets the number of virtual CPU cores the guest OSes can see. Oracle VM
VirtualBox supports symmetrical multiprocessing (SMP) and can present up to 32 virtual
CPU cores to each virtual machine.

Btw, the same section also states clearly the position regarding cores.

You should not configure virtual machines to use more CPU cores than are available physi-
cally. This includes real cores, with no hyperthreads.

Also note: adding cores to a VM does not necessarily make it work faster. In fact the opposite is usually true: any core assigned to a VM creates a context switching overhead. If that investment is not being repaid, i.e. if the core is standing idle, then it is nothing but overhead and the VM will be slower. Most users find 2 cores to be ideal.

A physical PC does not get slower if superfluous cores are added, because it isn't a VM: it doesn't have to switch contexts with a host. The extra cores aren't helping anything, but neither are they harming anything.

[mpack]

p.s. I'm taking your word for it that you at least have 40 real cores, though that would still be quite a monster. What is it, dual Xeons? I wouldn't trust any AMD claim about core count after they deliberately muddied the definition.