I don't think it needs to be system pre-emptable. If we reserve 1 core for the OS then the user can always interact with the system. The OS can tell them "App

I don't think it needs to be system pre-emptable. If we reserve 1 core for the OS then the user can always interact with the system. The OS can tell them "App X has pegged the 15 userland cores. Do you wish to kill it?". In practice, I'm not sure how relevant pre-empting is any more. Software is much better behaved than it used to and I rarely see these runaway processes anymore. And when they do it's usually pegging a single core at 100% while other processes share the remaining core.