Rate-monotonic scheduling (RMS) is a widely used real-time scheduling technique. This paper proposes RBound, a new admission control for RMS. RBound has two interesting properties. First, it achieves high processor utilization under certain conditions. We show how to obtain these conditions in a multiprocessor environment and propose a multiprocessor scheduling algorithm that achieves a near optimal processor utilization. Second, the framework developed for RBound remains close to the original RMS framework (that is, task dispatching is still done via a fixed-priority scheme based on the task periods). In particular, we show how RBound can be used to guarantee a timely recovery in the presence of faults and still achieve high processor utilization. We also show how RBound can be used to increase the processor utilization when aperiodic tasks are serviced by a priority exchange server or a deferrable server.

Many real-time multiprocessor scheduling techniques have been proposed to guarantee the timely execution of periodic preemptive real-time tasks. However timeliness is usually only guaranteed in the absence of faults, which may be unacceptable for some critical systems. We therefore address the problem of multiprocessor scheduling for preemptive real-time tasks so that the timeliness of the system can be guaranteed even in the presence of faults. This work focuses on global scheduling where tasks can migrate across processors. We consider two varieties of global multiprocessor scheduling: in the frame-based model, an aperiodic task set is scheduled to create a template (frame), and that schedule may be executed periodically. In the periodic model, each task in the set has a separate period, and is executed with no explicitly predetermined schedule. For each model, we show how to guarantee timely execution and recovery in the general case. We also propose solutions that improve upon this general case when all tasks require the same amount of time to recover from a fault.

The authors study GRMS, a global scheduling scheme for rate monotonic tasks on a multiprocessor. Several admission control algorithms for GRMS are presented, both for hard and soft real-time tasks. The average performance of these admission control algorithms is compared with the performance of known partitioning schemes. The result of these comparisons outlines some situations where one scheme is preferable over the other. Partitioning schemes are better suited for hard real-time systems, while a global scheme is preferable for soft real-time systems.