Exact speedup factors for linear-time schedulability tests for fixed-priority preemptive and non-preemptive scheduling

Brüggen, Georg von der; Chen, Jian-Jia; Davis, Robert I.; Huang, Wen-Hung

doi:10.1016/j.ipl.2016.08.001

Cited by 5 publications

(5 citation statements)

References 17 publications

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“…We note that it has recently been shown (von der Bruggen et al 2016) that the results comparing FP-P v. EDF-P, and FP-NP v. EDF-NP given in Table 1, which assume optimal priority assignment and exact schedulability tests, continue to hold when Deadline Monotonic priority assignment and simple, sufficient, linear-time schedulability tests are employed for fixed priority scheduling. Thus in these cases, in terms of the speedupfactors required, there is no penalty in using Deadline Monotonic priority assignment 5 and simple linear-time schedulability tests.…”

Section: Discussionmentioning

confidence: 82%

“…We note that speedup factors can lack the power to discriminate between the performance of different scheduling algorithms and schedulability tests even though their performance may be very different when viewed from the perspective of empirical evaluation (von der Bruggen et al 2016). The interested reader is referred to recent work by Chen et al (2017) for a full discussion of the pros and cons of using speedup factors and other resource augmentation metrics.…”

Section: S1mentioning

confidence: 98%

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Exact speedup factors and sub-optimality for non-preemptive scheduling

et al. 2017

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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 suboptimality 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.Preliminary publication: This paper extends initial research into speedup factors for preemptive versus non-preemptive uniprocessor scheduling published in RTSS 2015 (Davis et al. 2015c). The main extension is the proof of the exact speedup factor required to guarantee the FP-P feasibility of any FP-NP feasible constrained-deadline task set. Real-Time Syst (2018) 54:208-246 209 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 viceversa. 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.

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Section: Discussionmentioning

confidence: 82%

Section: S1mentioning

confidence: 98%

Exact speedup factors and sub-optimality for non-preemptive scheduling

et al. 2017

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“…that can be no greater than the bound determined under abstraction approximation. Similarly, in the arbitrary-deadline case, the upper bound of 2, holds even when the priority assignment policy used is deadline monotonic, a parameter restriction that is not optimal in this case, and a simple linear time schedulability test is used, again leading to a greatly simplified proof [69] for the upper bound with an exact test and optimal priority ordering.…”

Section: Parameter Relaxation Versus Parameter Restrictionmentioning

confidence: 99%

On the Trade-offs between Generalization and Specialization in Real-Time Systems

Brüggen

Burns

Chen

et al. 2022

2022 IEEE 28th International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA)

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While academia favours general research that is applicable to a large class of systems, this paper highlights the necessity of research into specific scenarios and aims to increase its acceptance in the real-time systems community. We argue that such research is not only motivated by greater applicability to industry, but that specialization can also provide valuable information from a purely academic perspective. In addition, the trade-offs between generalization and specialization are examined, considering not only theoretical performance, but also the impact on essential non-functional properties that are important for industry, namely composability, robustness, extensibility, and parametric simplicity.• Special Cases: When are special cases useful? Why is the exploration of special cases important and valuable?• General Cases: When are general cases useful? What should be considered when evaluating the quality of solutions and analyses for general cases? We motivate, and provide evidence for, a series of observations that distil the key differences between a focus on special rather than 1 This work covers a broad spectrum of topics related to real-time systems. We assume that the reader is familiar with basic concepts from the realtime systems literature, and therefore, to increase the reading flow, we do not introduce them in detail. Less common concepts and terminology related to a specific sub-problem are introduced in the appropriate section of the paper. A glossary of common real-time systems terminology can be found at https://site.ieee.org/tcrts/education/terminology-and-notation/.

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“…Under FP-P, ratemonotonic (RM-P) priority assignment is optimal [23] for implicit-deadline task sets. Under FP-NP, we explore RM-NP, which has been proved to have a resource augmentation bound of 1.76322 against the optimal workload-conserving 1 non-preemptive scheduling in [30,31]. By using RM-P and RM-NP, we know that all tasks in T x have higher priorities than all tasks in T if x < .…”

Section: System Modelmentioning

confidence: 99%

“…However, non-preemptive scheduling can still be applicable if the execution times of the tasks are short enough. For quantitive comparisons between preemptive and non-preemptive scheduling strategies based on resource augmentation factors, the recent results can be found in [13,30]. Moreover, von der Brüggen et al [31] and Andersson and Tovar [1] presented utilization-based analyses by incorporating the ratio of the blocking time, due to non-preemptive scheduling, to the execution time of a task.…”

Section: Introductionmentioning

confidence: 99%

Parametric utilization bounds for implicit-deadline periodic tasks in automotive systems

Brüggen

Ueter

Chen

et al. 2017

Proceedings of the 25th International Conference on Real-Time Networks and Systems

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Fixed-priority scheduling has been widely used in safetycritical applications. This paper explores the parametric utilization bounds for implicit-deadline periodic tasks in automotive uniprocessor systems, where the period of a task is either 1, 2, 5, 10, 20, 50, 100, 200, or 1000 milliseconds. We prove a parametric utilization bound of 90%+z for such automotive task systems under rate-monotonic preemptive scheduling (RM-P), where z is a parameter de ned by the input task set with 0 ≤ z ≤ 10%. Moreover, we explain how to perform an exact schedulability test for an automotive task set under RM-P by validating only three conditions. Furthermore, we extend our analyses to rate-monotonic non-preemptive scheduling (RM-NP). We show that very reasonable utilization values can still be achieved under RM-NP if the execution time of all tasks is below 1 millisecond. The analyses presented here are compatible with angle-synchronous tasks by applying the related arrival curves. It is shown in the evaluations that scheduling those angle-synchronous tasks according to their minimum inter-arrival time instead of assigning them to the highest priority can drastically increase the acceptance ratio in some settings.

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Exact speedup factors for linear-time schedulability tests for fixed-priority preemptive and non-preemptive scheduling

Cited by 5 publications

References 17 publications

Exact speedup factors and sub-optimality for non-preemptive scheduling

Exact speedup factors and sub-optimality for non-preemptive scheduling

On the Trade-offs between Generalization and Specialization in Real-Time Systems

Parametric utilization bounds for implicit-deadline periodic tasks in automotive systems

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