Revisiting the kernel's preemption models (part 1)

The main feature of full RT is that it is *deterministic* - things happen at precisely when predicted and expected. Latency or performance is not important and they can be sacrificed for the sake of correctness.

Servers can have a long latency for the sake of throughoutput and desktop users can prefer low latencies. While these deal with different pre-emption modes, they are not about real-timedness. So even in these cases boot-time selection is quite enough.