Versatile and efficient mixed–criticality scheduling for multi-core processors

Abstract : This thesis focuses on the scheduling of mixed-criticality scheduling algorithms for multi-processors. The correctness of the execution of the real-time applications is ensured by a scheduler and is checked during the design phase. The execution platform sizing aims at minimising the number of processors required to ensure this correct scheduling. This sizing is impacted by the safety requirements. Indeed, these requirements tend to overestimate the execution times of the applications to ensure their correct executions. Consequently, the resulting sizing is costly. The mixed-criticality scheduling theory aims at proposing compromises on the guarantees of the execution of the applications to reduce this over-sizing. Several models of mixed-criticality systems offering different compromises have been proposed but all are based on the use of execution modes. Modes are ordered and tasks have non decreasing execution times in each mode. Yet, to reduce the sizing of the execution platform, only the execution of the most critical tasks is ensured. This model is called the discarding model. For simplicity reasons, most of the mixed-criticality scheduling algorithms are limited to this model. Besides, the most efficient scheduling policies for multi-processors entail too many preemptions and migrations to be actually used. Finally, they are rarely generalised to handle different models of mixed-criticality systems. However, the handling of more than two execution modes or of tasks with elastic periods would make such solutions more attractive for the industry. The approach proposed in this thesis is based on the separation of concerns between handling the execution modes and the scheduling of the tasks on the multi-processors. With this approach, we achieve to design an efficient scheduling policy that schedules different models of mixed-criticality systems. It consists in performing the transformation of a mixed-criticality task set into a non mixed-criticality one. We then schedule this task set by using an optimal hard real-time scheduling algorithm that entails few preemptions and migrations: RUN. We first apply our approach on the discarding model with two execution modes. The results show the efficiency of our approach for such model. Then, we demonstrate the versatility of our approach by scheduling systems of the discarding model with more than two execution modes. Finally, by using a method based on the decomposition of task execution, our approach can schedule systems based on elastic tasks.
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Romain Gratia. Versatile and efficient mixed–criticality scheduling for multi-core processors. Other [cs.OH]. Télécom ParisTech, 2017. English. ⟨NNT : 2017ENST0001⟩. ⟨tel-01844389⟩

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