The 9th IEEE Real-Time and Embedded Technology and Applications Symposium, 2003. Proceedings.
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Abstract

We provide a constant time schedulability test for a multiprocessor server handling aperiodic tasks. Dhall?s effect is avoided by dividing the tasks in two priority classes based on task utilization: heavy and light. We prove that if the load on the multiprocessor server stays below Uthreshold = 3 - 7 \approx 35.425%, the server can accept incoming aperiodic tasks and guarantee that the deadlines of all accepted tasks will be met. 35.425% utilization is also a threshold for a task to be characterized as heavy. The bound Uthreshold = 3 - 7 \approx 35.425% is easy-to-use, but not sharp if we know the number of processors in the multiprocessor. For a server with m processors, we calculate a formula for the sharp bound Uthreshold(m), which converges to Uthreshold from above as m \rightarrow \infty. The results are based on a utilization function um(x) = 2(1 - x)/(2 + 2+2x) + x/m. By using this function, the performance of the multiprocessor can in some cases be improved beyond Uthreshold(m) by paying the extra overhead of monitoring the individual utilization of the current tasks.
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