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Exact Speedup Factors and Sub-Optimality for Non-Preemptive Scheduling


Rob Davis , Abhilash Thekkilakattil, Oliver Gettings , Radu Dobrin, Sasikumar Punnekkat, Jian-Jia Chen

Publication Type:

Journal article


Real-Time Systems


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 xed priority non-preemptive scheduling. Speci cally, we derive the exact processor speed-up factor required to guarantee the feasibility under FP-NP (i.e. schedulablability 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 xed 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.


author = {Rob Davis and Abhilash Thekkilakattil and Oliver Gettings and Radu Dobrin and Sasikumar Punnekkat and Jian-Jia Chen},
title = {Exact Speedup Factors and Sub-Optimality for Non-Preemptive Scheduling},
volume = {54},
pages = {1--39},
month = {October},
year = {2017},
journal = {Real-Time Systems},
url = {}