Adaptive Hierarchical Scheduling Framework for TiRTOS

Adaptive Hierarchical Scheduling Framework for TiRTOS

Hesham Hussien, Eman Shaaban, Said Ghoniemy
DOI: 10.4018/IJERTCS.2019010107
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The complexity of embedded real-time systems has increased, and most applications have large diversity in execution times of their tasks. Therefore, most traditional scheduling techniques do not satisfy requirements of such applications. This article proposes an adaptive hierarchical scheduling framework for a set of independent concurrent applications composing of soft and hard real time tasks, that run on a single processor. It ensures temporal partitioning between independent applications with budget adaption feature, where CPU time of each application is periodically and dynamically assigned. Implemented in the kernel of TI-RTOS on a resource constrained platform, experiments show that proposed scheme provides good performance for multiple applications with dynamic tasks under overload conditions. Compared with traditional priority scheduler originally implemented in TI-RTOS and EDF scheduler, it achieves low miss ratio with minimal overhead while yielding temporal partitioning.
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The research reviewed here can be traced back over the last few years, where distinguished researches and projects have demonstrated the effectiveness of hierarchical scheduling techniques of periodic tasks in RTOS.

It was initially proposed by researchers in (Deng, & Liu, (1997, December)), where they proposed a two level hierarchical scheduling framework considering the maximum task execution time (WCET), and it was proved to be resources wasting.

In (Davis, & Burns, (2005, December)), authors applied a fixed priority preemptive scheduling in HSF global and local levels considering sporadic, periodic and deferrable servers (Inam, Mäki-Turja, Sjödin, Ashjaei, & Afshar, (2011, September)) in their work. It guaranteed that tasks in highest levels would meet their deadlines while lowest level tasks may suffer from deadlines misses since it was based on (WCET) in their calculations. Hence critical tasks are assigned to high levels to ensure meeting their deadlines. In (Zhang, & Burns, (2007, December)), authors proposed an analysis of hierarchical EDF preemptive scheduling, depending on the earliest deadline first (EDF) scheduler introduced by (Liu & Layland, 1973). They presented a schedulability test for different hard real time application tasks when the local scheduler is EDF and the global scheduler is EDF or fixed priority. EDF scheduling is proved to have a better performance than fixed-priority scheduling in terms of deadline miss. However, it is difficult to ensure that critical tasks will meet their deadlines as it depends on the tasks deadlines which varing over the run time.

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