That page seems to be describing SCHED_FIFO processes, which are already a thing without PREEMPT_RT. Maybe they weren't back in the pre-2.6 days? Anyway, they are usually limited to 95% of total runtime by the sched_rt_runtime_us tunable, to avoid accidental self-DoSing. Maybe that, too, was later invention -- 2.6 is very very old.
The page goes on:
> A patch does exist to enable process to have real-time process access to any process requesting it.
According to the sched(7) man page, this has never been the case: before 2.6.12, the process had to have CAP_SYS_NICE; after, it was limited by policy through RLIMIT_RTPRIO. I guess it's possible that this was not the case for the original out-of-tree patch set.
But it's been there for many years, well before the 2020 edit that added the bulk of the current text on that wiki page.
The page goes on:
> A patch does exist to enable process to have real-time process access to any process requesting it.
According to the sched(7) man page, this has never been the case: before 2.6.12, the process had to have CAP_SYS_NICE; after, it was limited by policy through RLIMIT_RTPRIO. I guess it's possible that this was not the case for the original out-of-tree patch set.
But it's been there for many years, well before the 2020 edit that added the bulk of the current text on that wiki page.