Browsing by Author "Puaut, Isabelle"
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- An improved preemption delay upper bound for floating non-preemptive regionPublication . Marinho, José; Nélis, Vincent; Petters, Stefan M.; Puaut, IsabelleIn embedded systems, the timing behaviour of the control mechanisms are sometimes of critical importance for the operational safety. These high criticality systems require strict compliance with the offline predicted task execution time. The execution of a task when subject to preemption may vary significantly in comparison to its non-preemptive execution. Hence, when preemptive scheduling is required to operate the workload, preemption delay estimation is of paramount importance. In this paper a preemption delay estimation method for floating non-preemptive scheduling policies is presented. This work builds on [1], extending the model and optimising it considerably. The preemption delay function is subject to a major tightness improvement, considering the WCET analysis context. Moreover more information is provided as well in the form of an extrinsic cache misses function, which enables the method to provide a solution in situations where the non-preemptive regions sizes are small. Finally experimental results from the implementation of the proposed solutions in Heptane are provided for real benchmarks which validate the significance of this work.
- Cache-Persistence-Aware Response-Time Analysis for Fixed-Priority Preemptive SystemsPublication . Rashid, Syed Aftab; Nelissen, Geoffrey; Hardy, Damien; Åkesson, Benny; Puaut, Isabelle; Tovar, EduardoA task can be preempted by several jobs of higher priority tasks during its response time. Assuming the worst-case memory demand for each of these jobs leads to pessimistic worstcase response time (WCRT) estimations. Indeed, there is a big chance that a large portion of the instructions and data associated with the preempting task τj are still available in the cache when τj releases its next jobs. Accounting for this observation allows the pessimism of WCRT analysis to be significantly reduced, which is not considered by existing work. The four main contributions of this paper are: 1) The concept of persistent cache blocks is introduced in the context of WCRT analysis, which allows re-use of cache blocks to be captured, 2) A cache-persistence-aware WCRT analysis for fixed-priority preemptive systems exploiting the PCBs to reduce the WCRT bound, 3) An multi-set extension of the analysis that further improves the WCRT bound, and 4) An evaluation showing that our cache-persistence-aware WCRT analysis results in up to 10% higher schedulability than state-of-the-art approaches.
- Preemption delay analysis for floating non-preemptive region schedulingPublication . Marinho, José; Nélis, Vincent; Petters, Stefan M.; Puaut, IsabelleIn real-time systems, there are two distinct trends for scheduling task sets on unicore systems: non-preemptive and preemptive scheduling. Non-preemptive scheduling is obviously not subject to any preemption delay but its schedulability may be quite poor, whereas fully preemptive scheduling is subject to preemption delay, but benefits from a higher flexibility in the scheduling decisions. The time-delay involved by task preemptions is a major source of pessimism in the analysis of the task Worst-Case Execution Time (WCET) in real-time systems. Preemptive scheduling policies including non-preemptive regions are a hybrid solution between non-preemptive and fully preemptive scheduling paradigms, which enables to conjugate both world's benefits. In this paper, we exploit the connection between the progression of a task in its operations, and the knowledge of the preemption delays as a function of its progression. The pessimism in the preemption delay estimation is then reduced in comparison to state of the art methods, due to the increase in information available in the analysis.