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Unified overhead-aware schedulability analysis for slot-based task-splitting

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Abstract

Hard real- time multiprocessor scheduling has seen, in recent years, the flourishing of semi-partitioned scheduling algorithms. This category of scheduling schemes combines elements of partitioned and global scheduling for the purposes of achieving efficient utilization of the system’s processing resources with strong schedulability guarantees and with low dispatching overheads. The sub-class of slot-based “task-splitting” scheduling algorithms, in particular, offers very good trade-offs between schedulability guarantees (in the form of high utilization bounds) and the number of preemptions/migrations involved. However, so far there did not exist unified scheduling theory for such algorithms; each one was formulated in its own accompanying analysis. This article changes this fragmented landscape by formulating a more unified schedulability theory covering the two state-of-the-art slot-based semi-partitioned algorithms, S-EKG and NPS-F (both fixed job-priority based). This new theory is based on exact schedulability tests, thus also overcoming many sources of pessimism in existing analysis. In turn, since schedulability testing guides the task assignment under the schemes in consideration, we also formulate an improved task assignment procedure. As the other main contribution of this article, and as a response to the fact that many unrealistic assumptions, present in the original theory, tend to undermine the theoretical potential of such scheduling schemes, we identified and modelled into the new analysis all overheads incurred by the algorithms in consideration. The outcome is a new overhead-aware schedulability analysis that permits increased efficiency and reliability. The merits of this new theory are evaluated by an extensive set of experiments.

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Notes

  1. We use the term multiprocessor rather than multicore, because a lot of that work applies not only to multicore but also to other multiprocessor systems.

  2. Specifically, we only cover the main variant of NPS-F, which splits tasks between no more than two processors.

  3. We focus on S-EKG and not in EDF-SS, because latter is a version of the former that explores different bin-packing heuristics for assigning task-to-processors.

  4. Approaches exist for considerably reducing the length of the testing interval \(t\) (George et al. 1996; Spuri 1996; Ripoll et al. 1996; Hoang et al. 2006) in order to speed up the schedulability test, but would have required some amendments, in the presence of the scheduling overheads considered.

  5. That proof assumed implicit-deadline tasks; proof for arbitrary deadlines has not yet been published. In any case, in this work, we set \(\Omega \) accordingly.

  6. Available online at http://gmplib.org/

  7. The bursty periodic arrival model was introduced in Audsley et al. 1993.

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Acknowledgments

This work was partially supported by National Funds through FCT (Portuguese Foundation for Science and Technology) and by ERDF (European Regional Development Fund) through COMPETE (Operational Programme ‘Thematic Factors of Competitiveness’), within project(s) FCOMP-01-0124-FEDER-037281 (CISTER), FCOMP-01-0124-FEDER-020447 (REGAIN); by FCT and the EU ARTEMIS JU funding, within project ARTEMIS/0003/2012, JU grant number 333053 (CONCERTO); by the European Union, under the Seventh Framework Programme (FP7/2007-2013), grant agreement number 611016 (P-SOCRATES), by FCT and ESF (European Social Fund) through POPH (Portuguese Human Potential Operational Program), under PhD grant SFRH/BD/46199/2008.

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Authors and Affiliations

  1. Polytechnic Institute of Porto, CISTER/INESC-TEC, ISEP, 4200-072 , Porto, Portugal

    Paulo Baltarejo Sousa, Konstantinos Bletsas, Eduardo Tovar & Benny Åkesson

  2. ISR-Porto, FEUP, University of Porto, Porto, Portugal

    Pedro Souto

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  1. Paulo Baltarejo Sousa
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  2. Konstantinos Bletsas
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  3. Eduardo Tovar
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  4. Pedro Souto
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  5. Benny Åkesson
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Correspondence to Paulo Baltarejo Sousa.

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Sousa, P.B., Bletsas, K., Tovar, E. et al. Unified overhead-aware schedulability analysis for slot-based task-splitting. Real-Time Syst 50, 680–735 (2014). https://doi.org/10.1007/s11241-014-9204-x

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