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A Utilization Bound for Aperiodic Tasks and Priority Driven Scheduling
March 2004 (vol. 53 no. 3)
pp. 334-350

Abstract—Real-time scheduling theory offers constant-time schedulability tests for periodic and sporadic tasks based on utilization bounds. Unfortunately, the periodicity or the minimal interarrival-time assumptions underlying these bounds make them inapplicable to a vast range of aperiodic workloads such as those seen by network routers, Web servers, and event-driven systems. This paper makes several important contributions toward real-time scheduling theory and schedulability analysis. We derive the first known bound for schedulability of aperiodic tasks. The bound is based on a utilization-like metric we call synthetic utilization, which allows implementing constant-time schedulability tests at admission control time. We prove that the synthetic utilization bound for deadline-monotonic scheduling of aperiodic tasks is {\frac 1 {1 + \sqrt {1/2}}}. We also show that no other time-independent scheduling policy can have a higher schedulability bound. Similarly, we show that EDF has a bound of 1 and that no dynamic-priority policy has a higher bound. We assess the performance of the derived bound and conclude that it is very efficient in hit-ratio maximization.

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Index Terms:
Real-time scheduling, schedulability analysis, utilization bounds, aperiodic tasks.
Citation:
Tarek F. Abdelzaher, Vivek Sharma, Chenyang Lu, "A Utilization Bound for Aperiodic Tasks and Priority Driven Scheduling," IEEE Transactions on Computers, vol. 53, no. 3, pp. 334-350, March 2004, doi:10.1109/TC.2004.1261839
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