Recall we always say that we should not give all of our CPU cores to the guests so we do not kill the host. So I had a Windows Preview guest in Fusion Professional 12.2.1. The host is an iMac Pro on (what a coincidence) Monterey 12.2.1 with 8 processor cores. The guest had 2 processor cores and after one of the Dev channel updates could not run. In Activity Monitor I saw the guest vmx was using 100% of CPU. So I gave the guest 8 processor cores, and it still could not run, and the vmx was at 400%.
The Fusion UI lets me set up to 16 processor cores. I have hyper threading so 16 hyperthreads are available, and one would think that if I gave a guest 8 processor cores on an 8 processor core Mac I would see 800% in Activity Monitor not 400%? So I gave the guest 12 processor cores, and confirmed at 9 and above Fusion warns that you are using too many processor cores on your Mac. With 12 cores the guest topped out at 600% and then got some breathing room so I am trying to see if it will update to the next Preview release.
So what is the deal here? Is the Fusion UI seeing hyperthreads as processor cores and offering me 16? The UI did seem to know I only had 8 cores. Does Fusion simply offer 16 cores as a fixed menu option? Then in operation it seems clear that Fusion is using the hyperthreads rather than the cores as my 12 core guest should be killing my host? ?!?
