Some years ago I was working with VMware Server 1.0 on Windows 2003. I had 2 servers with VMware Server, one of them has one Hyper-threaded Intel CPU, and the other one has the same Intel CPU but with HT disabled.
I had a Virtual Machine running a 16 bit application, which took all the available CPU cycles. When this VM ran on the non-HT server, the Windows host reported 100% CPU usage. When the VM ran on the HT-enabled server, host CPU usage was 50%, and task manager showed the VM taking all the cycles from a half-processor and the other half-processor almost idle.
Assuming that CPUs were equal, my understanding is that the VM got more CPU power running on the non-HT server than running on the HT-enabled server (because HT divided by 2 the CPU, and assigned just a half CPU to the VM).
My question is, what happens with HT on ESX?
When I assign a vCPU to a VM, it will use just a half core in a Hyper-threaded server, but a full core on a HT-disabled server? (assuming no other VMs competing for resources).
Thanks and best regards.