基于时限单调算法的混合任务实时调度算法的研究与设计

Research and Design of a Deadline Monotonic Based Hybrid Tasks Real-time Static Priority Scheduling Algorithm

周期任务与非周期任务的混合调度是实时调度研究的一个重要方向。针对现代嵌入式实时系统的任务特性,和经典实时调度算法只调度周期任务的特点,提出一种新的静态优先级调度算法——混合任务时限单调算法(Periodic and Aperiodic Deadline Monotonic,PADM)。该方法结合时限单调(DM)算法和先来先服务(FCFS)算法,将非周期任务量化为周期任务,且非周期任务在其裕度为零时优先级最高。通过理论分析和具体实验比较,在任务集轻载情况下,PADM算法尽可能地保证周期任务的完成率和非周期任务的时限,同时所带来的额外开销小,计算复杂度低,实现方便,是一种有效的混合任务调度算法。

Hybrid scheduling of hard periodic and soft scheduling. We present a new static priority scheduling aperiodic task is a key issue of real-time algorithm PADM （Periodic and Aperiodic Deadline Monotonic） for this issue, which is based on the property of modem embedded real-time system and the characteristic of only scheduling for a period task of the classical real-time scheduling algorithm. The algorithm employs DM （Deadline Monotonic） and FCFS （First Come First Served） to quantify an aperiodic task into a period task, and the priority of an aperiodic task is the highest when its laxity is zero. Our experiments show that PADM can guarantee the finish rate of a periodic task and the time deadline of an aperiodic task when task load is light. It also has less overhead and lower computing complexity . It is easy to be implemented. PADM is therefore an effective hybrid tasks scheduling algorithm.