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The 9th IEEE Real-Time and Embedded Technology and Applications Symposium, 2003. Proceedings. (2003)
Toronto, Canada
May 27, 2003 to May 30, 2003
ISSN: 1080-1812
ISBN: 0-7695-1956-3
pp: 170
Lars Lundberg , Blekinge Institute of Technology
H?kan Lennerstad , Blekinge Institute of Technology
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 U<sub>threshold</sub> = 3 - \[\sqrt 7 \] \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.<div></div> The bound U<sub>threshold</sub> = 3 - \[\sqrt 7 \] \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 U<sub>threshold</sub>(m), which converges to U<sub>threshold</sub> from above as m \rightarrow \infty.<div></div> The results are based on a utilization function u<sub>m</sub>(x) = 2(1 - x)/(2 + \[\sqrt {2 + 2x} \]) + x/m. By using this function, the performance of the multiprocessor can in some cases be improved beyond U<sub>threshold</sub>(m) by paying the extra overhead of monitoring the individual utilization of the current tasks.

H. Lennerstad and L. Lundberg, "Global Multiprocessor Scheduling of Aperiodic Tasks using Time-Independent Priorities," The 9th IEEE Real-Time and Embedded Technology and Applications Symposium, 2003. Proceedings.(RTAS), Toronto, Canada, 2003, pp. 170.
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