Scheduling fixed-priority tasks with preemption threshold
Scheduling fixed-priority tasks with preemption threshold
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DOI：
10.1109/rtcsa.1999.811269
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发表时间：
1999-12
期刊：
影响因子：
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通讯作者：
Yun Wang;M. Saksena
中科院分区：
文献类型：
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作者：
Yun Wang;M. Saksena
在固定优先级调度的背景下，具有非抢先调度的任务集的可行性并不意味着具有先发制度调度的可行性，反之亦然。我们使用Express Logic在其ThreadX实时操作系统中首先引入的先发制阈值的概念来开发一个调度模型，该模型均包含先发制人和非抢先的固定优先级调度。抢先阈值允许任务仅将任务的预先设置为指定的阈值优先级。仍然允许具有高于阈值的优先级的任务抢占。通过这种新的调度模型，我们表明与先发制人和非剥夺计划模型相比，调度性得到了提高。我们使用Level-I繁忙时期的概念开发了计算最坏情况响应时间的方程式。提出了有关广义模型的一些有用结果，并根据这些结果设计了用于优先级和优先阈值的最佳分配算法。
In the context of fixed-priority scheduling, feasibility of a task set with non-preemptive scheduling does not imply the feasibility with preemptive scheduling and vice versa. We use the notion of preemption threshold, first introduced by Express Logic, in their ThreadX real-time operating system, to develop a scheduling model that subsumes both preemptive and non-preemptive fixed priority scheduling. Preemption threshold allows a task to only disable preemption of tasks up to a specified threshold priority. Tasks having priorities higher than the threshold are still allowed to preempt. With this new scheduling model, we show that schedulability is improved as compared to both the preemptive and nonpreemptive scheduling models. We develop the equations for computing the worst-case response times, using the concept of level-i busy period. Some useful results about the generalized model are presented and an algorithm for optimal assignment of priority and preemption threshold is designed based on these results.