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Extending rate monotonic analysis with exact cost of preemptions for hard realtime systems
 In ECRTS ’07: Proceedings of the 19th Euromicro Conference on RealTime Systems
, 2007
"... In this paper we study hard realtime systems composed of independent periodic preemptive tasks where we assume that tasks are scheduled by using Liu & Layland’s pioneering model following the Rate Monotonic Analysis (RMA). For such systems, the designer must guarantee that all the deadlines ..."
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In this paper we study hard realtime systems composed of independent periodic preemptive tasks where we assume that tasks are scheduled by using Liu & Layland’s pioneering model following the Rate Monotonic Analysis (RMA). For such systems, the designer must guarantee that all the deadlines of all the tasks are met, otherwise dramatic consequences occur. Certainly, guaranteeing deadlines is not always achievable because the preemption is approximated when using this analysis, and this approximation may lead to a wrong realtime execution whereas the schedulability analysis concluded that the system was schedulable. To cope with this problem the designer usually allows margins which are difcult to assess, and thus in any case lead to a waste of resources. This paper makes multiple contributions. First, we show that, when considering the cost of the preemption during the analysis, the critical instant does not occur upon simultaneous release of all tasks. Second, we provide a technique which counts the exact number of preemptions of each instance for all the tasks of a given system. Finally, we present an RMA extension which takes into account the exact cost due to preemption in the schedulability analysis rather than an approximation, thus yielding a new and stronger schedulability condition which eliminates the waste of resources since margins are not necessary. 1
Scheduling Algorithms for RealTime Systems
, 2005
"... Realtime systems are those whose correctness depends not only on logical results of computations, but also on the time at which the results are produced. This thesis provides a formal definition for realtime systems and includes the following original contributions on realtime scheduling algorith ..."
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Realtime systems are those whose correctness depends not only on logical results of computations, but also on the time at which the results are produced. This thesis provides a formal definition for realtime systems and includes the following original contributions on realtime scheduling algorithms. The first topic studied in the thesis is minimizing the total penalty to be paid in scheduling a set of soft realtime tasks. The problem is NPhard. We prove the properties of any optimal scheduling algorithm. We also derive a number of heuristic algorithms which satisfy the properties obtained. Moreover, we obtain a tight upper bound for the optimal solution to the problem. Numerical results that compare the upper bound with the optimal solution and the heuristic algorithms are provided. In the second part of this thesis, we study the problem of minimizing the number of processors required for scheduling a set of periodic preemptive independent hard realtime tasks. We use a partitioning strategy with an EDF scheduling algorithm on each processor. The problem is NPhard. We derive lower and upper bounds for the number of processors required to satisfy the constraints of the problem. We also compare a number of heuristic algorithms with each other and with the bounds derived in this research. Numerical results demonstrate that our lower bound is very tight. In the third part of the thesis, we study the problem of uplink scheduling in telecommunication systems with two dimensional resources. Our goal is to maximize the total value of the packets sent in uplink subframe such that system constraints and requirements are satisfied. The packets have various QoS requirements and have either soft or hard deadlines. We take two approaches, namely 01 and fractional approaches, to model the problem. Considering the properties of the application, we derive globally optimal solutions in polynomial time for the models. We also present a method to finetune the models. Numerical results are provided to compare the performance of the various optimal algorithms each corresponding to a model. i
Scheduling in Multiprocessor System using Genetic Algorithm
 International Journal of Advanced Science and Technology
, 2012
"... Task scheduling is essential for the suitable operation of multiprocessor systems. The task scheduling is prime significance of multiprocessor parallel systems. In this paper, an efficient method based on genetic algorithms is developed to solve the multiprocessor scheduling problem. The paper also ..."
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Task scheduling is essential for the suitable operation of multiprocessor systems. The task scheduling is prime significance of multiprocessor parallel systems. In this paper, an efficient method based on genetic algorithms is developed to solve the multiprocessor scheduling problem. The paper also aims to provide a comparative study of incorporating heuristics such as ‘Earliest Deadline First (EDF) ’ and ‘Shortest Computation Time First (SCTF) ’ separately with genetic algorithms. We exhibit efficiency of Node duplication Genetic Algorithm (NGA) based technique by comparing against some of the existing deterministic scheduling techniques for minimizing inter processor traffic communication. A comparative study of the results obtained from simulations shows that genetic algorithm can be used to schedule tasks to meet deadlines, in turn to obtain high processor utilization. Performance analysis of NGA is compared with GA, FCFS and List Scheduler. Experimental results show that the NGA is betters than the others. Performance of NGA, GA, List Scheduling, and FCFS is almost 64.1%, 55.55%, 52.08, and 41.033 % respectively.
A Modified Maximum Urgency First Scheduling Algorithm for RealTime Tasks
"... Abstract—This paper presents a modified version of the maximum urgency first scheduling algorithm. The maximum urgency algorithm combines the advantages of fixed and dynamic scheduling to provide the dynamically changing systems with flexible scheduling. This algorithm, however, has a major shortcom ..."
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Abstract—This paper presents a modified version of the maximum urgency first scheduling algorithm. The maximum urgency algorithm combines the advantages of fixed and dynamic scheduling to provide the dynamically changing systems with flexible scheduling. This algorithm, however, has a major shortcoming due to its scheduling mechanism which may cause a critical task to fail. The modified maximum urgency first scheduling algorithm resolves the mentioned problem. In this paper, we propose two possible implementations for this algorithm by using either earliest deadline first or modified least laxity first algorithms for calculating the dynamic priorities. These two approaches are compared together by simulating the two algorithms. The earliest deadline first algorithm as the preferred implementation is then recommended. Afterwards, we make a comparison between our proposed algorithm and maximum urgency first algorithm using simulation and results are presented. It is shown that modified maximum urgency first is superior to maximum urgency first, since it usually has less task preemption and hence, less related overhead. It also leads to less failed noncritical tasks in overloaded situations. Keywords—Modified maximum urgency first, maximum urgency first, realtime systems, scheduling. I.
A Fuzzy Algorithm for Scheduling Periodic Tasks on Multiprocessor Soft RealTime Systems
"... Summary In this paper we consider the use of fuzzy logic in the scheduling of periodic tasks in soft realtime multiprocessor systems. Most researches concerning realtime system scheduling assumes scheduling constraint to be precise. However, in many circumstances the values of these parameters ar ..."
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Summary In this paper we consider the use of fuzzy logic in the scheduling of periodic tasks in soft realtime multiprocessor systems. Most researches concerning realtime system scheduling assumes scheduling constraint to be precise. However, in many circumstances the values of these parameters are vague. The vagueness of parameters suggests that we make use of fuzzy logic to decide in what order the requests should be executed to better utilize the system and as a result reduce the chance of a request being missed. Our main contribution is proposing a fuzzy approach to multiprocessor realtime scheduling in which the scheduling parameters are treated as fuzzy variables. A simulation is also performed and the results are judged against each other. It is concluded that the proposed fuzzy approach is very promising and it has the potential to be considered for future research.
Technical Report No. 2005499 Scheduling Algorithms for RealTime Systems ∗
, 2005
"... The problem of realtime scheduling spans a broad spectrum of algorithms from simple uniprocessor to highly sophisticated multiprocessor scheduling algorithms. In this paper, we study the characteristics and constraints of realtime tasks which should be scheduled to be executed. Analysis methods an ..."
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The problem of realtime scheduling spans a broad spectrum of algorithms from simple uniprocessor to highly sophisticated multiprocessor scheduling algorithms. In this paper, we study the characteristics and constraints of realtime tasks which should be scheduled to be executed. Analysis methods and the concept of optimality criteria, which leads to design appropriate scheduling algorithms, will also be addressed. Then, we study realtime scheduling algorithms for uniprocessor systems, which can be divided into two major classes: offline and online. Online algorithms are partitioned into either static or dynamicpriority based algorithms. We discuss both preemptive and nonpreemptive staticpriority based algorithms. For dynamicpriority based algorithms, we study the two subsets; namely, planning based and best effort scheduling algorithms. Some of the uniprocessor scheduling algorithms are illustrated by examples in the Appendix. Multiprocessor scheduling algorithms is another class of realtime scheduling algorithms which is discussed in the paper as well. We also describe techniques to deal with aperiodic and sporadic tasks, precedence constraints, and priority inversion.
Deadline vs. Laxity as a Decision Parameter in Fuzzy RealTime Scheduling
"... Abstract. Many algorithms have been proposed for scheduling realtime tasks to guarantee the timing requirements of such a system. Each of those algorithms is based on a decision parameter with which the algorithm determines the order of the tasks to be executed. Among those parameters, deadline and ..."
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Abstract. Many algorithms have been proposed for scheduling realtime tasks to guarantee the timing requirements of such a system. Each of those algorithms is based on a decision parameter with which the algorithm determines the order of the tasks to be executed. Among those parameters, deadline and laxity are the most important ones which have been employed in the Earliest Deadline First (EDF) and the Least Laxity First (LLF) algorithms respectively [1]. Furthermore, to include the implicit constraints imposed by real world, such as uncertainty and lack of complete knowledge about the environment, dynamicity in the world, bounded validity time of information and other resource constraints, a few fuzzy approaches have been proposed [2, 3]. It was shown that the fuzzy approaches outperform the nonfuzzy approaches. The main purpose of this paper is to study and compare the behavior of a realtime system when the fuzzy scheduler is based on deadline and when it is based on laxity. The obtained results show that deadline is a better parameter to be considered in fuzzy realtime scheduling. Keywords: Realtime Scheduling, Fuzzy Logic, EDF, LLF I.
IADIS International Conference Applied Computing 2006 A FUZZY ALGORITHM FOR REALTIME SCHEDULING OF SOFT PERIODIC TASKS ON MULTIPROCESSOR SYSTEMS
"... Many scheduling algorithms have been studied to guarantee the time constraints of realtime processes. Scheduling decision of these algorithms is usually based on parameters which are assumed to be crisp. However, in many circumstances the values of these parameters are vague. The vagueness of param ..."
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Many scheduling algorithms have been studied to guarantee the time constraints of realtime processes. Scheduling decision of these algorithms is usually based on parameters which are assumed to be crisp. However, in many circumstances the values of these parameters are vague. The vagueness of parameters suggests that we make use of fuzzy logic to decide in what order the requests should be executed to better utilize the system and as a result reduce the chance of a request being missed. Our main contribution is proposing a fuzzy approach to multiprocessor realtime scheduling in which the scheduling parameters are treated as fuzzy variables. A simulation is also performed and the results are judged against each other. It is concluded that the proposed fuzzy approach is very promising and it has the potential to be considered for future research.
Enhanced Maximum Urgency First Algorithm with Intelligent Laxity for Real Time Systems
"... In this paper Enhanced Maximum Urgency First (EMUF) scheduling algorithm with intelligent laxity has been proposed. This algorithm is a further improvement in MMUF algorithm [1] and is a mixed priority scheduling algorithm which combines the advantages of both fixed and dynamic scheduling for better ..."
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In this paper Enhanced Maximum Urgency First (EMUF) scheduling algorithm with intelligent laxity has been proposed. This algorithm is a further improvement in MMUF algorithm [1] and is a mixed priority scheduling algorithm which combines the advantages of both fixed and dynamic scheduling for better CPU utilization and throughput. The prime objective of this paper is to improve modified maximum urgency first scheduling (MMUF) using intelligent laxity as the dynamic priority. EMUF algorithm is mainly suited for real time systems where meeting of deadlines is an important criterion for scheduling. This proposed algorithm improves the Modified Maximum Urgency First scheduling algorithm for real time tasks proposed by V.Salmani et.al [1] and the experimental analysis shows that the proposed
States Graph Generation from dynamic Priority Time Petri Nets
"... (Communicated by Noômen Jarboui) dynamic Priority Time Petri Nets (dPTPN) is a mathematical formalism dedicated to modeling RealTime System (RTS) and checking its schedulability. The present paper proposes a states graph generation from a reduced dPTPN model in order to deal with the scheduling a ..."
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(Communicated by Noômen Jarboui) dynamic Priority Time Petri Nets (dPTPN) is a mathematical formalism dedicated to modeling RealTime System (RTS) and checking its schedulability. The present paper proposes a states graph generation from a reduced dPTPN model in order to deal with the scheduling analysis. Based on hierarchical modeling, the present model presents only the interaction between all RTS components and excluding their internal behavior. According to this reduction, a new denition of state is given. Hence, all reachable states and edges connecting between them are generated to show a prediction of the RTS scheduling. Thus, the resulting graph gives birth to an open research area in the purpose of checking its properties and deducing the schedulability.