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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.
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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