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Research on Key Technology in Weakly-Hard Real-Time System

Author: WuTong
Tutor: JinShiYao
School: National University of Defense Science and Technology
Course: Computer Science and Technology
Keywords: Real-time systems Weakly hard real-time Scheduling algorithm Dynamic failure Quality of service Fixed-length window constraints Variable-length window constraints CDBS AWCS (KWCS) Feedback mechanism
CLC: TP316.2
Type: PhD thesis
Year: 2008
Downloads: 159
Quote: 3
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With the development of computing technology, the types of real-time applications increasing number of expanding the range of applications of real-time systems, the increasing complexity of the system, especially with the development of network technology to promote the network for real-time applications, such as network multimedia, distance learning, tele-surgery etc., task completion of these applications have time constraints, but such time constraints neither as stringent as hard real-time, unlike the weak real-time as ill-defined, but based on the quality of service requirements. In order to better cope with the task types of real-time systems, complex constraints with instantaneous overload characteristics, the weak hard real-time theory emerged. Weakly hard real theory as a specification, perfect to enrich the theory of real-time systems, unified description of the the original various types of real-time system, hard real-time and soft real-time are actually weakly hard real-time systems, a special case. Weakly hard real-time to meet the needs of the new characteristics of the real-time system. Because of its hard real-time, weak real-time unified, and therefore easier to deal with many types of task scheduling; weakly hard real-time quality of service requirements of the two parameters describing the task, in order to more clearly define and distinguish the quality of service of the task ; system overload by weakly hard real-time scheduling algorithms provide a slow degradation of the quality of service. In this paper, to further enrich the weakly hard real-time constraints specification and weakly hard real-time scheduling algorithm is carried out in-depth research, productive work and innovative made in the following aspects: 1) This paper enriches the weak hard real-time constraints specification proposed (p, k) constraints, and prove the equivalence constraint (m, p), and thus can be exported relationship with the other weakly hard real-time constraints. (M, p) constraints, and (p, k) constraint of the different emphasis, the former projecting the number of consecutive lost deadline, which highlights the user to consider the minimum window. Further, the loss rate (p, k) is defined, and is given by (p, k) lost rate satisfies (p, k) constraints of the necessary conditions to provide a theoretical basis for classification selection algorithm. 2) In this paper, a class cut-based scheduling algorithm for solving variable-length window constraint violation discriminant cropped weak hard real-time scheduling (Cut-Down Based Scheduling constraints based on the (m, p), CDBS ) algorithm. Effective cut through the execution of the task sequence, and the introduction of the concept of the turning point, so that the constraint on the (m, p) satisfies the discriminant complexity is greatly reduced, and has nothing to do with the sequence length. The clipping algorithm correctness proof is given in the text, and its effectiveness is verified by experiment. In this paper, a simple priority allocation strategy, allocate tasks based on the the distance m consecutive losing deadline distance priority scheduling, and the combination of the four states of the task may appear. Finally, the algorithms and EDF, the DWCS, DBP algorithm compares the CDBS algorithm in terms of dynamic loss of efficiency and minimum success rate provides the appropriate compromise, has considerable performance compared with other algorithms. 3) This paper presents an arbitrary window constrained scheduling algorithm, assurance issues, research in services provide fair and carrier case different from the loss rate of the variable-length window. Design constraints based on the (p, k), an arbitrary window constraint scheduling (Any Window Constraint Scheduling, AWCS) algorithm, analyzing AWCS complexity of the algorithm, and in accordance with its sharp increase in complexity not suitable for scheduling re-through load conditions proposed simplified algorithm K window constrained scheduling (K-Window Constraint Scheduling, KWCS) algorithm. The experiment showed that KWCS having the AWCS similar performance and complexity is substantially reduced, and therefore KWCS more suitable for the actual system applications. Fairness and differential analysis of AWCS (KWCS) provide further define the success rate deviates from, and given scheduling algorithm delay upper bound of General said method. Finally, the algorithm and other weak hard real-time scheduling algorithm compares AWCS (KWCS) The results show that re-through overload situations better than the other algorithms, and can make the task of QoS degradation slowly, providing a fair but differentiated services . 4) the practical application of the K window constrained scheduling algorithm rich expansion. Proposed KWCS and DBP, hybrid algorithm, the system over-load conditions is divided into mild over-contained critical over-upload and re-spent upload, dynamic monitoring system of the state, and according to the different overloads take different scheduling policies, and thus solve the KWCS in mild before upload the problem of poor performance in the case; for KWCS algorithm needs to save the history of the state and not conducive to the expansion of issues, proposed classification selection algorithm, based on the (p, k) loss ratio, to be classified on the (p, k) flow, thereby improving the algorithm scalability; proposed multi-hop K the window constraint scheduling (Multihop KWCS, M-KWCS) algorithm, to solve the KWCS application in an end-to-end system. 5) weakly hard real-time scheduling algorithm attempts in the exploration of new application areas. Proposed multiprocessor weakly hard real-time scheduling algorithm to solve the multi-processor, multi-class task scheduling, and consider the resources shared / exclusive access; proposed simple feedback-based hybrid static / dynamic energy saving weakly hard real-time scheduling algorithm for the actual execution time of the task is usually far less than the actual situation of the worst-case execution time of mixed static / dynamic energy saving weakly hard real-time scheduling algorithm to improve the introduction of the division of tasks, estimated task execution time of the feedback mechanism, in order to obtain lower the speed of execution, to achieve better energy-saving effect. The experiments show that, when the average execution time is less than the worst-case execution time is large, the new algorithm is superior to the original algorithm, energy savings up to 60% to 70%, minimum energy savings of about 10%. Inadequacies of the algorithm is that when the average execution time is close to the worst-case execution time, the new algorithm is more energy-consuming than the original algorithm. Finally, the general summary of the full text, and pointed out that the issue needs further study and perfect.

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