Joint scheduling of distributed complex periodic and hard aperiodic tasks in statically scheduled systems

In this paper we present algorithms for the joint scheduling of periodic and aperiodic tasks in statically scheduled distributed real-time systems. Periodic tasks are precedence constrained, distributed, and communicating over the nodes of the systems. Both soft and hard aperiodic tasks are handled. After a static schedule has been created in a first step, the algorithms determine the amount and distribution of unused resources and leeway in it. These are then used to incorporate aperiodic tasks into the schedule by shifting the periodic tasks' execution, without violating their feasibility. Run-time mechanisms are simple and require only little memory. Processors and communication nodes can be utilized fully. The algorithm performs on optimal online guarantee algorithm for hard aperiodic tasks of O(N). An extensive simulation study exhibits very high guarantee ratios for various load and deadline scenarios, which underlines the efficiency of our method.