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- Afshar, Sara
(författare)
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Lock-Based Resource Sharing for Real-Time Multiprocessors
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Embedded systems are widely used in the industry and are typically resource constrained, i.e., resources such as processors, I/O devices, shared buffers or shared memory might be limited in the system. Hence, techniques that can enable an efficient usage of processor bandwidths in such systems are of great importance. Locked-based resource sharing protocols are proposed as a solution to overcome resource limitation by allowing the available resources in the system to be safely shared. In recent years, due to a dramatic enhancement in the functionality of systems, a shift from single-core processors to multi-core processors has become inevitable from an industrial perspective to tackle the raised challenges due to increased system complexity. However, the resource sharing protocols are not fully mature for multi-core processors. The two classical multi-core processor resource sharing protocols, spin-based and suspension-based protocols, although providing mutually exclusive access to resources, can introduce long blocking delays to tasks, which may be unacceptable for many industrial applications. In this thesis we enhance the performance of resource sharing protocols for partitioned scheduling, which is the de-facto scheduling standard for industrial real-time multi-core processor systems such as in AUTOSAR, in terms of timing and memory requirements. A new scheduling approach uses a resource efficient hybrid approach combining both partitioned and global scheduling where the partitioned scheduling is used to schedule the major number of tasks in the system. In such a scheduling approach applications with critical task sets use partitioned scheduling to achieve higher level of predictability. Then the unused bandwidth on each core that is remained from partitioning is used to schedule less critical task sets using global scheduling to achieve higher system utilization. These scheduling schema however lacks a proper resource sharing protocol since the existing protocols designed for partitioned and global scheduling cannot be directly applied due to the complex hybrid structure of these scheduling frameworks. In this thesis we propose a resource sharing solution for such a complex structure. Further, we provide the blocking bounds incurred to tasks under the proposed protocols and enhance the schedulability analysis, which is an essential requirement for real-time systems, with the provided blocking bounds.
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| 2. |
- Marković, Filip, 1992-
(författare)
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Preemption-Delay Aware Schedulability Analysis of Real-Time Systems
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Schedulability analysis of real-time systems under preemptive scheduling may often lead to false-negative results, deeming a schedulable taskset being unschedulable. This is the case due to the inherent over-approximation of many time-related parameters such as task execution time, system delays, etc., but also, in the context of preemptive scheduling, a significant over-approximation arises from accounting for task preemptions and corresponding preemption-related delays. To reduce false-negative schedulability results, it is highly important to as accurately as possible approximate preemption-related delays. Also, it is important to obtain safe approximations, which means that compared to the approximated delay, no higher corresponding delay can occur at runtime since such case may lead to false-positive schedulability results that can critically impact the analysed system. Therefore, the overall goal of this thesis is:To improve the accuracy of schedulability analyses to identify schedulable tasksets in real-time systems under fixed-priority preemptive scheduling, by accounting for tight and safe approximations of preemption-related delays.We contribute to the domain of timing analysis for single-core real-time systems under preemptive scheduling by proposing two novel cache-aware schedulability analyses: one for fully-preemptive tasks, and one for tasks with fixed preemption points. Also, we propose a novel method for deriving safe and tight upper bounds on cache-related preemption delay of tasks with fixed preemption points. Finally, we contribute to the domain of multi-core partitioned hard real-time systems by proposing a novel partitioning criterion for worst-fit decreasing partitioning, and by investigating the effectiveness of different partitioning strategies to provide task allocation which does not jeopardize the schedulability of a taskset in the context of preemptive~scheduling.
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