> What if the thread is polling some hardware and gets interrupted right
> when it should be getting some important data before it is overwritten?
Should polling hardware be the task of the kernel, especially if it is so sensitive to timing?
> I think the default should be 'illimited' indeed, and changeable at run
> time via proc or sys, so everyone can make their choice.
If "everyone can make their choice" anyway, why not have the default to be limited to a sensible value so that the choice to betray themselves are made only consciously?
Be reminded that people (distributions) do use SCHED_FIFO, e.g., to play movie in a way that video hopefully sync with audio. It isn't nice if such programs would "normally" be risky of getting their computers hung up.