Apparently the timeslice of the SCHED_RR process varies with nice level
the same way that it does for SCHED_OTHER. So while niceness doesn't
affect the priority of a SCHED_RR task, it does impact how much cpu it gets.
SUSv3 indicates, "Any processes or threads using SCHED_FIFO or SCHED_RR
shall be unaffected by a call to setpriority()."
The code in set_user_nice() has a comment that leads me to believe the
current behaviour is accidental (although I think the "not" in the last
line isn't meant to be there):
/*
* The RT priorities are set via sched_setscheduler(), but we still
* allow the 'normal' nice value to be set - but as expected
* it wont have any effect on scheduling until the task is
* not SCHED_NORMAL/SCHED_BATCH:
*/
It appears that the desired behaviour is to allow setting the nice level
of a realtime task, but to not have it affect anything until (and
unless) it drops that realtime status. Is this correct?
Chris
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