Scheduling of low-priority background processes

[Thomas Koeller]

Dear kernel wizards,

first of all, I wish to apologize in case I am asking a questions that has already been discussed much on this list. I am not a subscriber
(so please CC. me if you respond to this mail) and by browsing the list archive I did not immediatly find any discussion about my topic.
So here is my question:

Some operating systems I have been working with had a scheduling policy different from what I find in Linux, where all regular processes
execute at priiority zero, the lowest one possible. I am talking of real-time priorities here, of course, not nice values. On those systems,
you could assign a scheduling priority lower than the one nomally used by interactive processes to CPU-hogging, numbercrunching
tasks. These tasks would then use up any CPU time left over by interactive processes without otherwise interfering with them. I always
found this feature very useful (think of SETI@home!).

It appears to me that this feature could easily be integrated into Linux, by just