Summary: Fair Integrated Scheduling of Soft Real-time Tardiness Classes on
UmaMaheswari C. Devi and James H. Anderson
Department of Computer Science, The University of North Carolina, Chapel Hill, NC
Prior work on Pfair scheduling has resulted in three optimal multiprocessor scheduling algorithms, and one algorithm,
EPDF, that is less expensive but not optimal. EPDF is still of interest in soft real-time systems, however, due to its ability to
guarantee bounded tardiness. In particular, it has been shown that a tardiness bound of t quanta is possible under EPDF if all
task weights (i.e., shares or utilizations) are restricted to a value specified as a function of t. In an actual system, however,
different tasks may be subject to different tardiness bounds. If such a system is scheduled under EPDF, then the tardiness
of a task with a higher bound may cause the tardiness bound of a task with a lower bound to be violated; that is, temporal
isolation among the various tardiness classes may not be guaranteed. In this paper, we propose an algortihm based on EPDF
for scheduling task classes with different tardiness bounds on a multiprocessor. Our algorithm provides temporal isolation
among classes, allows the available processing capacity to be fully utilized, and does not require that previously established
per-task weight restrictions be made more stringent.
Work supported by NSF grants CCR 9988327, ITR 0082866, CCR 0204312, and CCR 0309825.
Pfair scheduling, originally introduced by Baruah et al.
, is the only known way of optimally scheduling recurrent
real-time tasks on multiprocessors. Under Pfair schedul-