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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
We consider the scheduling of a sporadic real-time task system on an identical multiprocessor. Though Pfair
algorithms are theoretically optimal for such task systems, in practice, their runtime overheads can significantly
reduce the amount of useful work that is accomplished. On the other hand, if all deadlines need to be met,
then every known non-Pfair algorithm requires restrictions on total system utilization that can approach ap-
proximately 50% of the available processing capacity. This may be overkill for soft real-time systems, which
can tolerate occasional or bounded deadline misses (i.e., bounded tardiness). In this paper we derive tardiness
bounds under preemptive and non-preemptive global EDF when the total system utilization is not restricted,
except that it not exceed the available processing capacity. Hence, processor utilization can be improved for
soft real-time systems on multiprocessors. Our tardiness bounds depend on the total system utilization and
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, CNS 0408996, CCF 0541056, and CNS 0615197, and by ARO


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


Collections: Computer Technologies and Information Sciences