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An \(\mathsf{EDF}\) -based restricted-migration scheduling algorithm for multiprocessor soft real-time systems

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Abstract

There has been much recent interest in the use of the earliest-deadline-first ( \(\mathsf{EDF}\) ) algorithm for scheduling soft real-time sporadic task systems on identical multiprocessors. In hard real-time systems, a significant disparity exists between \(\mathsf{EDF}\) -based schemes and Pfair scheduling: on M processors, the worst-case schedulable utilization for all known \(\mathsf{EDF}\) variants is approximately M/2, whereas it is M for optimal Pfair algorithms. This is unfortunate because \(\mathsf{EDF}\) -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 \(\mathsf{EDF}\) (i.e. , global \(\mathsf{EDF}\) ) can ensure bounded tardiness for a sporadic task system with no restrictions on total utilization. Unrestricted task migrations in global \(\mathsf{EDF}\) 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 \(\mathsf{EDF-fm}\) , which is based upon \(\mathsf{EDF}\) and treads a middle path, by restricting, but not eliminating, task migrations. Specifically, under \(\mathsf{EDF-fm}\) , 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. \(\mathsf{EDF-fm}\) , like global \(\mathsf{EDF}\) , can ensure bounded tardiness to a sporadic task system as long as the available processing capacity is not exceeded, but, unlike global \(\mathsf{EDF}\) , may require that per-task utilizations be capped. The required cap is quite liberal, hence, \(\mathsf{EDF-fm}\) should enable a wide range of soft real-time applications to be scheduled with no constraints on total utilization.

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Authors and Affiliations

  1. Department of Computer Science, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA

    James H. Anderson, Vasile Bud & UmaMaheswari C. Devi

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  1. James H. Anderson
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  2. Vasile Bud
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  3. UmaMaheswari C. Devi
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Correspondence to UmaMaheswari C. Devi.

Additional information

Work supported by NSF grants CCR 0204312, CNS 0309825, CNS 0408996, and CNS 0615197, and by ARO grant W911NF-06-1-0425. The third author was also supported by an IBM Ph.D. fellowship. A preliminary version of this paper was published in (Andersow, J., et al. in Proceedings of the 17th Euromicro Conference on Real-Time Systems, pp. 199–208, 2005).

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Anderson, J.H., Bud, V. & Devi, U.C. An \(\mathsf{EDF}\) -based restricted-migration scheduling algorithm for multiprocessor soft real-time systems. Real-Time Syst 38, 85–131 (2008). https://doi.org/10.1007/s11241-007-9035-0

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