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Tardiness Bounds under Global EDF Scheduling on a Multiprocessor

Summary: Tardiness Bounds under Global EDF Scheduling on a
UmaMaheswari C. Devi and James H. Anderson
Department of Computer Science
The University of North Carolina at Chapel Hill
This paper considers the scheduling of soft real-time sporadic task systems under global EDF on an iden-
tical multiprocessor. Though Pfair scheduling is theoretically optimal for hard real-time task systems on
multiprocessors, it can incur significant run-time overhead. Hence, other scheduling algorithms that are not
optimal, including EDF, have continued to receive considerable attention. However, prior research on such
algorithms has focussed mostly on hard real-time systems, where, to ensure that all deadlines are met, ap-
proximately 50% of the available processing capacity will have to be sacrificed in the worst case. This may
be overkill for soft real-time systems that can tolerate deadline misses by bounded amounts (i.e., bounded
tardiness). In this paper, we derive tardiness bounds under preemptive and non-preemptive global EDF on
multiprocessors when the total utilization of a task system is not restricted and may equal the number of pro-
cessors. Our tardiness bounds depend on per-task utilizations and execution costs -- the lower these values,
the lower the tardiness bounds. As a final remark, we note that global EDF may be superior to partitioned
EDF for multiprocessor-based soft real-time systems in that the latter does not offer any scope to improve
system utilization even if bounded tardiness can be tolerated.
Work supported by NSF grants CCR 0204312, CNS 0309825, and CNS 0408996. The first author was also supported by an IBM


Source: Anderson, James - Department of Computer Science, University of North Carolina at Chapel Hill


Collections: Computer Technologies and Information Sciences