This is why the distinction between soft and hard realtime exists. Linux-rt makes linux actually decent at soft realtime. PREEMPT_RT usually results on measure

This is why the distinction between soft and hard realtime exists. Linux-rt makes linux actually decent at soft realtime. PREEMPT_RT usually results on measured peak latency for realtime tasks (SCHED_RR/SCHED_FIFO) on the order of a few hundred usec. Standard Linux lets latency go to tens of milliseconds, easily verifiable by running cyclictest from rt-tests for a few hours while using the computer. Needless to say, this is unacceptable for many user cases, including pro audio, videoconference and even gaming. In contrast, AmigaOS's exec.library had no trouble yielding solid sub-millisecond behaviour in 1985, on a relatively slow 7MHz 68000. No amount of patching Linux can give you hard realtime, as it is about hard guarantees, backed up by proofs built from formal verification, which Linux is excluded from due to its sheer size. There's a few RTOSs that are formally verified, but I only know one that provides process isolation via the usual supervisor vs user CPU modes virtualization model: seL4.