Summary: Fair Scheduling of Dynamic Task Systems on
Anand Srinivsan and James H. Anderson
Department of Computer Science, University of North Carolina
Chapel Hill, NC 27599-3175 USA
In dynamic real-time task systems, tasks that are subject to deadlines are al-
lowed to join and leave the system. In previous work, Stoica et al. and Baruah et al.
presented conditions under which such joins and leaves may occur in fair-scheduled
uniprocessor systems without causing missed deadlines. In this paper, we extend
their work by considering fair-scheduled multiprocessors. We show that their con-
ditions are sufficient on M processors, under any deadline-based Pfair scheduling
algorithm, if the utilization of every subset of M - 1 tasks is at most one. Further,
for the general case in which task utilizations are not restricted in this way, we
derive sufficient join/leave conditions for the PD2 Pfair algorithm. We also show
that, in general, these conditions cannot be improved upon without causing missed
Key words: Dynamic task systems, Pfairness, multiprocessor, real-time scheduling
In many real-time systems, the set of runnable tasks may change dynamically.