Static priority scheduling of aperiodic real-time tasks

Abstract

We investigate deadline meeting properties of the well-known (preemptive) static priority scheduling (SPS) algorithm, which is widespreadly used in commercial real-time operating system kernels. A discrete-time single server queueing system employing SPS for scheduling probabilistically arriving tasks at L priority levels is considered for this purpose. Model parameters are arrival and execution-time distribution A𝓁(z), L𝓁(z) and a (constant) deadline T𝓁∈ 𝒯L per level l. By means of a combinatorial technique (which does not require stable-state assumptions), we determine the probability distribution of the (random-)time the system operates without violating any task's deadline. This distribution is asymptotically exponential with parameter λ 𝒯 L , which decreases exponentially with the deadlines 𝒯L; simple asymptotic expressions for λ 𝒯 L and all associated quantities (probabilities, moments,…) for large 𝒯L are provided. Our numerical examples suggest that real-time systems based on SPS operate reasonably well only if computing performance is (more than) adequate. © 1997 John Wiley & Sons, Inc. Random Struct. Alg., 10, 257–303 (1997)