周期性实时任务LLF调度算法改进

摘要

In order to reduce the times of laxity calculation and system scheduling, the least laxity first (LLF) scheduling algorithm for periodic real-time tasks is improved. The LLF queue is introduced into the system processing procedures; when the laxity of tasks is equal, the task with the earliest deadline is close to the top of the queue. Pre-execution time is introduced into task control block (TCB), after the task is scheduled, if there is no more urgent task, the execution task withdraws from the processor at the end of the pre-execution time. Matlab simulation tests show that the improvement of algorithm effectively reduces the times of laxity calculation of periodic real-time tasks and the times of system scheduling, and enhances the utilization of the processor.%为减少松弛度计算和系统调度次数,对周期性实时任务的最低松弛度优先(LLF)调度算法进行了改进.在系统处理过程中引入最低松弛度优先队列,当任务松弛度相同时,开始截止时刻早的任务靠近队首.在任务控制块(TCB)中引入预执行时间,任务被调度以后,如果没有更为紧迫的任务到达,任务执行到预执行时间结束才退出处理器.Matlab仿真试验表明,改进算法有效减少了周期件实时任务的松弛度计算次数和系统调度次数,提高了处理器的利用率.