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Issue No. 09 - September (2008 vol. 57)
ISSN: 0018-9340
pp: 1261-1276
Robert I. Davis , University of York, York
Attila Zabos , University of York, York
Alan Burns , University of York, York
Efficient exact schedulability tests are required both for on-line admission of applications to dynamic systems and as an integral part of design tools for complex distributed real-time systems. This paper addresses performance issues with exact Response Time Analysis (RTA) for fixed priority pre-emptive systems. Initial values are introduced that improve the efficiency of the standard RTA algorithm (i) when exact response times are required, and (ii) when only exact schedulability need be determined. The paper also explores modifications to the standard RTA algorithm, including; the use of a response time upper bound to determine when exact analysis is needed, incremental computation aimed at faster convergence, and checking tasks in reverse priority order to identify unschedulable tasksets early. The various initial values and algorithm implementations are compared by means of experiments on a PC recording the number of iterations required, and execution time measurements on a real-time embedded microprocessor. Recommendations are provided for engineers tasked with the problem of implementing exact schedulability tests, as part of on-line acceptance tests and spare capacity allocation algorithms, or as part of off-line system design tools.
Multiprocessing/multiprogramming/multitasking, Scheduling, Real-time systems and embedded systems

A. Zabos, A. Burns and R. I. Davis, "Efficient Exact Schedulability Tests for Fixed Priority Real-Time Systems," in IEEE Transactions on Computers, vol. 57, no. , pp. 1261-1276, 2008.
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