Recent applications of the Internet of Things and cyber-physical systems require the integration of many sensing and control tasks into resource-constrained embedded devices. Such tasks can often tolerate a bounded number of timing violations. The concept of weakly hard real-time systems can effectively improve resource efficiency without sacrificing system safety. However, the existing studies have limitations on their practical use due to the restrictions imposed on the task timing behavior, high analysis complexity, and the lack of multicore support. In this article, we propose a new job-class-level fixed-priority preemptive scheduler and its schedulability analysis framework for weakly hard real-time tasks. Our proposed scheduler employs the meet-oriented classification of jobs of a task in order to reduce the worst-case temporal interference imposed on other tasks. Under this approach, each job is associated with a “job-class” that is determined by the number of deadlines previously met (with a bounded number of consecutively missed deadlines). This approach allows decomposing the complex weakly hard schedulability problem into two subproblems that are easier to solve: 1) analyzing the response time of a job with each job-class, which can be done by an extension of the existing task-level analysis and 2) finding possible job-class patterns, which can be modeled as a simple reachability tree. We also present a semipartitioned task allocation method for multicore platforms, which enhances the schedulability of weakly hard tasks under the proposed scheduling framework. Experimental results indicate that our scheduler outperforms the prior work in terms of task schedulability and analysis time complexity. We have also implemented a prototype of a job-class-level scheduler in the Linux kernel running on Raspberry Pi with acceptably small-runtime overhead.

中文翻译：

---

走向实用的弱硬实时系统：作业类级别的调度方法


物联网和网络物理系统的最新应用需要将许多传感和控制任务集成到资源受限的嵌入式设备中。此类任务通常可以容忍有限数量的时序违规。弱硬实时系统的概念可以在不牺牲系统安全的情况下有效提高资源效率。然而，由于任务时序行为的限制、分析复杂度高以及缺乏多核支持，现有研究在实际应用中存在局限性。在本文中，我们提出了一种新的作业类级固定优先级抢占式调度器及其针对弱硬实时任务的可调度性分析框架。我们提出的调度程序采用面向满足的任务作业分类，以减少对其他任务施加的最坏情况时间干扰。在这种方法下，每项工作都与一个“工作类别”相关联，该“工作类别”由之前满足的截止日期数量（连续错过截止日期的数量有限）确定。这种方法允许将复杂的弱硬可调度性问题分解为两个更容易解决的子问题：1）分析每个作业类别的作业响应时间，这可以通过扩展现有的任务级分析来完成，2） ）寻找可能的工作类别模式，可以将其建模为简单的可达性树。我们还提出了一种适用于多核平台的半分区任务分配方法，该方法增强了所提出的调度框架下弱硬任务的可调度性。实验结果表明，我们的调度器在任务可调度性和分析时间复杂度方面优于先前的工作。 我们还在 Raspberry Pi 上运行的 Linux 内核中实现了作业类级别调度程序的原型，运行时开销在可接受的范围内。