Davis, Robert Ian orcid.org/0000-0002-5772-0928, Thekkilakattil, Abhilash, Gettings, Oliver et al. (3 more authors) (2017) Exact Speedup Factors and Sub-Optimality for Non-Preemptive Scheduling. Real-Time Systems. pp. 1-39. ISSN 1573-1383
Abstract
Fixed priority scheduling is used in many real-time systems; however, both preemptive and non-preemptive variants (FP-P and FP-NP) are known to be sub-optimal when compared to an optimal uniprocessor scheduling algorithm such as preemptive earliest deadline first (EDF-P). In this paper, we investigate the sub-optimality of fixed priority non-preemptive scheduling. Specifically, we derive the exact processor speed-up factor required to guarantee the feasibility under FP-NP (i.e. schedulability assuming an optimal priority assignment) of any task set that is feasible under EDF-P. As a consequence of this work, we also derive a lower bound on the sub-optimality of non-preemptive EDF (EDF-NP). As this lower bound matches a recently published upper bound for the same quantity, it closes the exact sub-optimality for EDF-NP. It is known that neither preemptive, nor non-preemptive fixed priority scheduling dominates the other, in other words, there are task sets that are feasible on a processor of unit speed under FP-P that are not feasible under FP-NP and vice-versa. Hence comparing these two algorithms, there are non-trivial speedup factors in both directions. We derive the exact speed-up factor required to guarantee the FP-NP feasibility of any FP-P feasible task set. Further, we derive the exact speed-up factor required to guarantee FP-P feasibility of any constrained-deadline FP-NP feasible task set.
Metadata
Authors/Creators: |
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Copyright, Publisher and Additional Information: | © The Author(s) 2017. | ||||||
Keywords: | Real-time, Uniprocessor , Resource augmentation, Speedup factor, Sub-optimality, Non-preemptive scheduling, Preemptive scheduling, EDF , Fixed priority | ||||||
Dates: |
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Institution: | The University of York | ||||||
Academic Units: | The University of York > Faculty of Sciences (York) > Computer Science (York) | ||||||
Funding Information: |
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Depositing User: | Pure (York) | ||||||
Date Deposited: | 04 Jan 2018 17:10 | ||||||
Last Modified: | 06 Dec 2023 12:12 | ||||||
Published Version: | https://doi.org/10.1007/s11241-017-9294-3 | ||||||
Status: | Published | ||||||
Refereed: | Yes | ||||||
Identification Number: | https://doi.org/10.1007/s11241-017-9294-3 |