Global multiprocessor scheduling of aperiodic tasks using time-independent priorities

• 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-threshold = 3 - root7 = 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 U-threshold = 3 - root7 approximate to 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-threshold(m), which converges to U-threshold from above as m --> infinity. The results are based on a utilization function u(m)(x) = 2(1-x)/(2+ root2+2x)+x/m. By using this function, the performance of the multiprocessor can in some cases be improved beyond U-threshold(m) by paying the extra overhead of monitoring the individual utilization of the current tasks.

Ämnesord

NATURVETENSKAP  -- Data- och informationsvetenskap -- Programvaruteknik (hsv//swe)

NATURAL SCIENCES  -- Computer and Information Sciences -- Software Engineering (hsv//eng)

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