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Flexible Tardiness Bounds for Sporadic Real-Time Task Systems on Multiprocessors

Summary: Flexible Tardiness Bounds for Sporadic Real-Time Task
Systems on Multiprocessors
UmaMaheswari C. Devi and James H. Anderson
Department of Computer Science
The University of North Carolina at Chapel Hill
October, 2005
The earliest-deadline-first (EDF) scheduling of a sporadic real-time task system on a multiprocessor
may require that the total utilization of the task system, Usum, not exceed (m + 1)/2 on m processors
if every deadline needs to be met. In recent work, we considered the alleviation of this under-utilization
for task systems that can tolerate deadline misses by bounded amounts (i.e., bounded tardiness). We
showed that if Usum m and tasks are not pinned to processors, then the tardiness of each task is
bounded under both preemptive and non-preemptive EDF. The tardiness bounds that we derived are
dependent upon the utilizations and execution costs of the constituent tasks, but are independent of
Usum. Furthermore, any task may incur maximum tardiness. In this paper, we address the issue of
supporting tasks whose tolerance to tardiness is less than that known to be possible under EDF. We
propose a new scheduling policy, called EDF-hl, that is a variant of EDF, and show that under EDF-hl,
any tardiness, including zero tardiness, can be ensured for a limited number of privileged tasks, and that
bounded tardiness can be guaranteed to the remaining tasks if their utilizations are restricted. EDF-hl
reduces to EDF in the absence of privileged tasks. The tardiness bound that we derive is a function


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


Collections: Computer Technologies and Information Sciences