The biggest problem is that context switching overhead becomes the main "work" being done, rather than the actual work of the threads, for some core count n (wh

The biggest problem is that context switching overhead becomes the main "work" being done, rather than the actual work of the threads, for some core count n (which depends on workload). You can already saturate an entire core just copying data from a NIC. Of course, enter BPF and all that jazz. Plus it doesn't play as nice with BIG.little multiprocessing (AMP - asymmetric multiprocessing). edit: I should note I am not advocating getting rid of preemption entirely, because it is needed for at least one processor, but having a fixed quantum causing a context switch on application CPUs is highly disruptive, both from the operation itself, and from blowing the cache all the time. Incidentally, one of the main reason for green threads.