Processor configuration is misleading

[byron.hawkins]

The processor allocation section of the VM Settings dialog is misleading. Throughout the Settings dialog, the range of the sliders matches the quantity of the corresponding resource that is available on the host. For example, my host has 12G ram, and the "RAM" slider offers the respective range of 4MB to 12288MB. But the "CPUs" slider offers a range of 1 to 16 CPUs for my single-socket i7 host. It appears to the VirtualBox user that a selection of n CPUs will allocate n hardware threads to the VM. But my machine does not have 16 hardware threads, it only has 8. Attempting to run any VM with more than 8 "CPUs" cause a massive load on my actual 8 hardware threads, because it is nearly impossible for the hardware to accommodate such a heavy load. I would also suspect that even selecting as many as 6 "CPUs" would not perform well, because the guest will think it has 6 cores, which is quite different than the 6 hardware threads on 3 cores which are actually available. A quick search of the VirtualBox forum shows that many people are confused about what is being allocated when n "CPUs" are selected, and their VMs are performing very badly as a result. I recommend limiting the "CPUs" slider range to the number of physical cores in the host. If it is really necessary for users to be able to virtualize processors that don't exist, this allocation can be made possible through the command-line interface using language that makes evident the actual behavior of such a VM; for example, "VBoxManage cpu-overload +6" would allocate 6 more cores than the host can actually provide.

[Frank Mehnert]

As of VBox 4.3.0, the GUI uses the physical cores on the host.