An EDF-based restricted-migration scheduling algorithm for multiprocessor soft real-time systems
There has been much recent interest in the use of the earliest-deadline-first ( {expression} ) algorithm for scheduling soft real-time sporadic task systems on identical multiprocessors. In hard real-time systems, a significant disparity exists between {expression} -based schemes and Pfair schedulin...
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Veröffentlicht in: | Real-time systems 2008-02, Vol.38 (2), p.85-131 |
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Sprache: | eng |
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Zusammenfassung: | There has been much recent interest in the use of the earliest-deadline-first ( {expression} ) algorithm for scheduling soft real-time sporadic task systems on identical multiprocessors. In hard real-time systems, a significant disparity exists between {expression} -based schemes and Pfair scheduling: on M processors, the worst-case schedulable utilization for all known {expression} variants is approximately M/2, whereas it is M for optimal Pfair algorithms. This is unfortunate because {expression} -based algorithms entail lower scheduling and task-migration overheads. However, such a disparity in schedulability can be alleviated by easing the requirement that all deadlines be met, which may be sufficient for soft real-time systems. In particular, in recent work, we have shown that if task migrations are not restricted, then {expression} (i.e. , global {expression} ) can ensure bounded tardiness for a sporadic task system with no restrictions on total utilization. Unrestricted task migrations in global {expression} may be unappealing for some systems, but if migrations are forbidden entirely, then bounded tardiness cannot be guaranteed. In this paper, we address the issue of striking a balance between task migrations and system utilization by proposing an algorithm called {expression}, which is based upon {expression} and treads a middle path, by restricting, but not eliminating, task migrations. Specifically, under {expression}, the ability to migrate is required for at most M-1 tasks, and it is sufficient that every such task migrate between two processors and at job boundaries only. {expression}, like global {expression}, can ensure bounded tardiness to a sporadic task system as long as the available processing capacity is not exceeded, but, unlike global {expression}, may require that per-task utilizations be capped. The required cap is quite liberal, hence, {expression} should enable a wide range of soft real-time applications to be scheduled with no constraints on total utilization. |
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ISSN: | 0922-6443 |
DOI: | 10.1007/s11241-007-9035-0 |