Allocating more cores than physically available leads to instability instead of just bad performance

[Jarrad Whitaker]

When using a Linux guest on Windows 7 x64 host, allocating 4 CPUs to my Linux guests (tested with Debian Testing as of the date of this bug report, and Ubuntu 11.04) leads to the guest either suddenly completely hanging (Ubuntu) or unable to launch any new processes (Debian). I have a dual core i5 with hyperthreading - as such I have the (albiet stupid) option to allocate four CPU cores to a VM. As a new user I did not make the connection that over-allocating was such a bad thing - this wasn't helped by the fact that VirtualBox displayed green for 1-4 CPUs, and red for anything over that.

Two issues that would be nice to have fixed: 1) overallocating, even though bad, should not lead to instability. 2) VirtualBox's UI should provide some indication that the user is overallocating cores. At the moment the green slider region can mislead inattentive users such as myself into thinking it's perfectly OK, and indeed a good thing, to allocate four CPUs on a host with four virtual cores but only two physical cores.

[Frank Mehnert]

There is no "fix" possible. The guest can freak out if certain (virtual) CPUs are not properly scheduled.