Execution times and execution jitter analysis of real-time tasks under fixed-priority pre-emptive scheduling

In this paper, we present worst-case and best-case execution times and (absolute) execution jitter analysis of independent, periodically activated, hard real-time tasks that are executed on a single processor under fixed-priority pre-emptive scheduling (FPPS), arbitrary phasing, (absolute) activation jitter, and deadlines at most equal to (worst-case) periods minus activation jitter. We prove that the worst-case and best-case execution time of a task are equal to its worst-case and best-case response time, respectively. We present an upper bound for execution jitter of a task expressed in terms of its best-case and worst-case execution time. We briefly consider execution times and execution jitter in other settings, such as distributed multiprocessor systems with task dependencies, tasks with arbitrary deadlines, and tasks with multiple operating modes. Execution jitter analysis is particularly valuable for real-time control systems to determine the variations in sampling-actuation delays of control tasks.

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