A Necessary Test for Fixed-Priority Real-Time Multiprocessor Systems based on Lazy-adversary Simulation

Abstract

Many embedded systems have real-time requirements which are sometimes hard and must be guaranteed at design time, although most embedded systems have soft deadlines in the sense that they can be missed without any catastrophe being caused by that. Scheduling simulations can be used as a necessary but not sufficient schedulability test that is useful for both hard and soft real-time systems. They help to assess the pessimism of formal analysis applied to hard real-time systems and they can be used as test-case generators during the design of soft real-time systems. In this paper, we present a new adversary simulator for multiprocessors with global task queue and fixed-priority scheduling. We consider sporadic tasks with constrained deadlines (D ≤ T). An adversary simulator uses the non-determinism in the arrivals of sporadic tasks to stress the system scheduler with valid arrival patterns. The simulator proposed in this paper applies a lazy approach that delays the arrival of high-priority tasks in order to form gangs that will preclude the execution of a victim task. We show that the new lazy-adversary simulator presented in this paper outperforms the previously existing necessary schedulability tests.