Games run in a tight loop, they don’t (typically) yield execution. If you don’t have preemption, a game will use 100% of all the resources all the time, if given the chance.
Even for non-rendering systems those still usually run at game tick-rates since running those full-tilt can starve adjacent cores depending on false sharing, cache misses, bus bandwidth limits and the like.
I can't think of a single title I worked on that did what you describe, embedded stuff for sure but that's a whole different class that is likely not even running a kernel.
Do no syscalls. Timer tick. Kernel takes over and does whatever as well.
No_HZ_FULL, isolated cpu cores, interrupts on some other core and you can spin using 100% cpu forever on a core. Do games do anything like this?
I haven't heard of it being done with PC games. I doubt the environment would be predictable enough. On consoles tho..?
From what I recall we mostly did it for predictability so that things that may go long wouldn't interrupt deadline sensitive things(audio, physics, etc).