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20
FixedPriority EndToEnd Scheduling In Distributed RealTime Systems
, 1997
"... In recent years more and more realtime applications run on multiprocessor or distributed systems. In such systems, a task may execute sequentially on many different processors. Such a task can be viewed as a linear chain of subtasks, each of which represents a segment of the task that executes on o ..."
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Cited by 40 (0 self)
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In recent years more and more realtime applications run on multiprocessor or distributed systems. In such systems, a task may execute sequentially on many different processors. Such a task can be viewed as a linear chain of subtasks, each of which represents a segment of the task that executes on one of those processors. The response time of the task is measured from the release of its first subtask to the completion of its last subtask and is called the endtoend response time. A task is schedulable if its endtoend response time is never greater than the specified endtoend relative deadline. This thesis deals with the problem of scheduling periodic tasks to meet their endtoend deadlines. Specifically, the thesis focuses on fixedpriority scheduling algorithms, where each subtask is assigned a fixed priority and is scheduled preemptively. According to this approach, three related problems need to be solved. Priority Assignment : How we assign the priorities to subtasks so that...
Improving scalability of task allocation and scheduling in large distributed realtime systems using shared buffers
 in Proceedings of the 9th Realtime/Embedded Technology and Applications Symposium (RTAS
, 2003
"... Scheduling precedenceconstrained tasks in a distributed realtime system is an NPhard problem. As a result, the task allocation and scheduling algorithms that use these heuristics do not scale when applied to large distributed systems. In this paper, we propose a novel approach that eliminates int ..."
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Cited by 30 (1 self)
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Scheduling precedenceconstrained tasks in a distributed realtime system is an NPhard problem. As a result, the task allocation and scheduling algorithms that use these heuristics do not scale when applied to large distributed systems. In this paper, we propose a novel approach that eliminates intertask dependencies using shared buffers between dependent tasks. The system correctness, with respect to datadependency, is ensured by having each dependent task poll the shared buffers at a fixed rate. Tasks can, therefore, be allocated and scheduled independently of their predecessors. To meet the timing constraints of the original dependenttask system, we have developed a method to iteratively derive the polling rates based on endtoend deadline constraints. The overheads associated with the shared buffers and the polling mechanism are minimized by clustering tasks according to their communication and timing constraints. Our simulation results with the task allocation based on a simple firstfit bin packing algorithm showed that the proposed approach scales almost linearly with the system size, and clustering tasks greatly reduces the polling overhead. 1
OffLine and OnLine CallScheduling in Stars and Trees
 in Proceedings of the 23rd International Workshop on GraphTheoretic Concepts in Computer Science, WG ‘97, LNCS1335, SpringerVerlag
, 1997
"... . Given a communication network and a set of call requests, the goal is to find a minimum makespan schedule for the calls such that the sum of the bandwidth requirements of simultaneously active calls using the same link does not exceed the capacity of that link. In this paper the callschedulin ..."
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Cited by 11 (2 self)
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. Given a communication network and a set of call requests, the goal is to find a minimum makespan schedule for the calls such that the sum of the bandwidth requirements of simultaneously active calls using the same link does not exceed the capacity of that link. In this paper the callscheduling problem is studied for star and tree networks. Lower and upper bounds on the worstcase performance of ListScheduling (LS) and variants of it are obtained for callscheduling with arbitrary bandwidth requirements and either unit call durations or arbitrary call durations. LS does not require advance knowledge of call durations and, hence, is an online algorithm. It has performance ratio (competitive ratio) at most 5 in star networks. A variant of LS for calls with unit durations is shown to have performance ratio at most 2 2 3 . In tree networks with n nodes, a variant of LS for calls with unit durations has performance ratio at most 6, and a variant for calls with arbitrary d...
Task Graph Performance Bounds Through Comparison Methods
, 2001
"... When a parallel computation is represented in a formalism that imposes seriesparallel structure on its task graph, it becomes amenable to automated analysis and scheduling. Unfortunately, its execution time will usually also increase as precedence constraints are added to ensure seriesparallel str ..."
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Cited by 6 (1 self)
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When a parallel computation is represented in a formalism that imposes seriesparallel structure on its task graph, it becomes amenable to automated analysis and scheduling. Unfortunately, its execution time will usually also increase as precedence constraints are added to ensure seriesparallel structure. Bounding the slowdown ratio would allow an informed tradeoff between the benefits of a restrictive formalism and its cost in loss of performance. This dissertation deals with seriesparallelising task graphs by adding precedence constraints to a task graph, to make the resulting task graph seriesparallel. The weak bounded slowdown conjecture for seriesparallelising task graphs is introduced. This states that the slowdown is bounded if information about the workload can be used to guide the selection of which precedence constraints to add. A theory of best seriesparallelisations is developed to investigate this conjecture. Partial evidence is presented that the weak slowdown bound is likely to be 4/3, and this bound is shown to be tight.
Timing analysis for resource access interference on adaptive resource arbiters
 in RealTime and Embedded Technology and Applications Symposium (RTAS), 2011 17th IEEE. IEEE
"... Abstract—Modern multiprocessor and multicore architectures adopt shared resources to meet increased performance requirements. Adaptive arbiters, such as FlexRay, have been adopted to grant access to shared resources. While increasing the performance, timing analysis is more challenging with this kin ..."
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Cited by 6 (2 self)
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Abstract—Modern multiprocessor and multicore architectures adopt shared resources to meet increased performance requirements. Adaptive arbiters, such as FlexRay, have been adopted to grant access to shared resources. While increasing the performance, timing analysis is more challenging with this kind of arbiter. This paper considers realtime tasks that are composed of superblocks, while superblocks themselves are composed of phases. Phases are characterized by their worstcase computation time on their processing element and their worstcase number of access requests to a shared resource. Resource accesses, such as access to caches or scratchpad memory, are synchronous and cause the processing element to stall until the access is served. Based on dynamic programming, we develop an algorithm that safely derives an upperbound of the worstcase response time of a phase. The worstcase response time of a task can then be determined for both sequential or timetriggered execution of superblocks. Experimental results are conducted for a realworld application. KeywordsWorstcase timing analysis, shared resource access, realtime embedded systems, FlexRay protocol. I.
Timed automata model for componentbased realtime systems
 In Proceedings of the 2010 17th IEEE International Conference and Workshops on the Engineering of ComputerBased Systems, ECBS ’10
, 2010
"... Abstract—One of the key challenges in modern realtime embedded systems is safe composition of different software components. Formal verification techniques provide the means for designtime analysis of these systems. This paper introduces an approach based on timed automata for analysis of such com ..."
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Abstract—One of the key challenges in modern realtime embedded systems is safe composition of different software components. Formal verification techniques provide the means for designtime analysis of these systems. This paper introduces an approach based on timed automata for analysis of such componentbased realtime embedded systems. The goal of our research is to provide a method for treating the schedulability problem of such systems on multicore platforms. Since the components are developed, analyzed and tested independent of each other, the impact of one component on the others does not depend on its internal structure. Therefore, we reduce the problem of proving the schedulability of the composed system to proving the schedulability of each component on the resource partition allocated to it based on the interface of the component. The proposed verification method is demonstrated on a H.264 decoder case study. Keywordsrealtime scheduling; model checking; components I.
Minimizing the makespan for a UET bipartite graph on a single processor with an integer precedence delay
, 2001
"... We consider a set of tasks of unit execution times and a bipartite precedence delays graph with a positive precedence delay d : an arc (i; j) of this graph means that j can be executed at least d time units after the completion time of i. The problem is to sequence the tasks in order to minimize ..."
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Cited by 1 (0 self)
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We consider a set of tasks of unit execution times and a bipartite precedence delays graph with a positive precedence delay d : an arc (i; j) of this graph means that j can be executed at least d time units after the completion time of i. The problem is to sequence the tasks in order to minimize the makespan. Firstly, we prove that the associated decision problem is NPcomplete. Then, we provide a non trivial polynomial time algorithm if the degree of every tasks from one of the two sets is 2. Lastly, we give an approximation algorithm with ratio 3 2 . 1
Scheduling to Minimize the Makespan on Identical Parallel Machines: An LPBased Algorithm
, 1998
"... Polyhedral Combinatorics approaches have turned out to be successful computational tools in many hard Combinatorial Optimization problems. We present an approximation algorithm based on linear programming formulations with binary decision variables which are a kind of assignment variables for the cl ..."
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Polyhedral Combinatorics approaches have turned out to be successful computational tools in many hard Combinatorial Optimization problems. We present an approximation algorithm based on linear programming formulations with binary decision variables which are a kind of assignment variables for the classical deterministic scheduling problem of minimizing the makespan on identical machines. The problem is known to be NPhard in the strong sense. The structure of the corresponding polytope is analyzed, and the strong cutting planes are identified. Computational results show that, in all tested cases, the problem can be solved exactly.
Timing Analysis for Resource Access Interference on Adaptive Resource Arbiters
"... Abstract—Modern multiprocessor and multicore architectures adopt shared resources to meet increased performance requirements. Adaptive arbiters, such as FlexRay, have been adopted to grant access to shared resources. While increasing the performance, timing analysis is more challenging with this k ..."
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Abstract—Modern multiprocessor and multicore architectures adopt shared resources to meet increased performance requirements. Adaptive arbiters, such as FlexRay, have been adopted to grant access to shared resources. While increasing the performance, timing analysis is more challenging with this kind of arbiter. This paper considers realtime tasks that are composed of superblocks, while superblocks themselves are composed of phases. Phases are characterized by their worstcase computation time on their processing element and their worstcase number of access requests to a shared resource. Resource accesses, such as access to caches or scratchpad memory, are synchronous and cause the processing element to stall until the access is served. Based on dynamic programming, we develop an algorithm that safely derives an upperbound of the worstcase response time of a phase. The worstcase response time of a task can then be determined for both sequential or timetriggered execution of superblocks. Experimental results are conducted for a realworld application. Keywords—Worstcase timing analysis, shared resource access, realtime embedded systems, FlexRay protocol. I.