> I will agree that it increases the unpredictability of execution time, > and if I wanted to guarantee I could meet deadlines I'd turn it off.
Turning it off may indeed improve predictability of execution time in some cases. Especially if the various active threads have different real-time priorities. For non-real-time threads, turning it off would just replace the hardware's scheduler unpredictability with that of the OS. For really hard real-time, of course, you still have many other sources of unpredictability: the cache(s), the TLB, the branch prediction, ... Stefan