Uniprocessor Static Priority Scheduling with Limited Priority Levels
优先级有限时的单处理器静态优先级调度

In practice, the schedulability of static priority scheduling may be reduced when priority levels of the system are insufficient. If a task set requires more priority levels than the system can support, several tasks must be assigned the same priority level. This causes the priority mapping problem. To solve it, a priority mapping algorithm and necessary and sufficient conditions for analyzing the schedulability of a task after priority mapping are needed. There are three kinds of priority mapping algorithms: decreasing priority assignment algorithm, increasing priority assignment algorithm, and threshold segment mapping algorithm. This paper presents implementation and analyzing conditions of algorithms. Properties of the algorithms are also described and showed. Performance of the algorithms is compared through simulations. Simulation results and conclusions are useful for designing and implementing real-time embedded systems.