本文基于随机模型研究了软实时系统中任务的可调度性特征，提出了期望可调度性的概念．期望可调度性是与实时任务到达时间t相关的，因此，提出的方法能研究任务子集在任意给定时间间隔的可调度性特征．本文给出了期望可调度性的条件，如果任务的持续时问满足该条件，则实时任务具有期望可调度性．基于理论结果的数值分析与模拟结果是一致的，这表明当软实时系统的负载率小于69％（某些确定性模型提供的）时，实时任务总是期望可调度的．这一结果也表明基于随机模型的期望可调度性方法能为软实时系统的任务可调度性分析提供一个更大的阈值和更好的适应性．%By studying the characteristics of the taskschedulability of stochastic tasks in a soft realtime system, we develop the expected schedulability conceptually. The expected schedulability is closely related with the arrival time of a real task; hence the proposed method can be applied to investigate the schedulability of a subset of tasks in any given timeinterval. The condition for expected schedulability is given. If the duration of a real task satisfies this condition, it is schedulable. Because simulation results show a good agreement with analytical ones, we confirm that the real tasks are always schedulable when the loading factor of the soft realtime system is smaller than 69%（as for some deterministic model）. This indicates that the proposed method of expected schedulability based on the stochastic model can provide a large threshold value and a better adaptability for soft realtime systems.
展开▼
