CPU contention is one of the least noticeable overload situations on a computer because schedulers have hidden it well since forever. Even if your video playba

CPU contention is one of the least noticeable overload situations on a computer because schedulers have hidden it well since forever. Even if your video playback and your benchmark are at the same nice-value, the scheduler notices that the benchmark is using lots more CPU, so it gets effectively "niced" compared to the video playback, which then gets the CPU whenever it's runnable. If someone swapped out your RAM for something less than the working set of the programs you have running -- you would notice. Also, if it were an I/O benchmark instead of a CPU benchmark -- you would notice. (Yes, there are I/O schedulers now, that help somewhat.) I/O and memory are not as trivial for a kernel to "make room" in by kicking out other programs.