Download or read book Scheduling Sequential Or Parallel Hard Real time Pre emptive Tasks Upon Identical Multiprocessor Platforms written by Pierre Courbin and published by . This book was released on 2013 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The scheduling of tasks on a hard real-time system consists in finding a way to choose, at each time instant, which task should be executed on the processor so that each succeed to complete its work before its deadline. In the uniprocessor case, this problem is already well studied and enables us to do practical applications on real systems (aerospace, stock exchange etc.). Today, multiprocessor platforms are widespread and led to many issues such as the effective use of all processors. In this thesis, we explore the existing approaches to solve this problem. We first study the partitioning approach that reduces this problem to several uniprocessor systems and leverage existing research. For this one, we propose a generic partitioning algorithm whose parameters can be adapted according to different goals. We then study the semi-partitioning approach that allows migrations for a limited number of tasks. We propose a solution with restricted migration that could be implemented rather simply on real systems. We then propose a solution with unrestricted migration which provides better results but is more difficult to implement. Finally, programmers use more and more the concept of parallel tasks that can use multiple processors simultaneously. These tasks are still little studied and we propose a new model to represent them. We study the possible schedulers and define a way to ensure the schedulability of such tasks for two of them.

Download or read book Multiprocessor Scheduling for Real Time Systems written by Sanjoy Baruah and published by Springer. This book was released on 2015-01-02 with total page 234 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive overview of both theoretical and pragmatic aspects of resource-allocation and scheduling in multiprocessor and multicore hard-real-time systems. The authors derive new, abstract models of real-time tasks that capture accurately the salient features of real application systems that are to be implemented on multiprocessor platforms, and identify rules for mapping application systems onto the most appropriate models. New run-time multiprocessor scheduling algorithms are presented, which are demonstrably better than those currently used, both in terms of run-time efficiency and tractability of off-line analysis. Readers will benefit from a new design and analysis framework for multiprocessor real-time systems, which will translate into a significantly enhanced ability to provide formally verified, safety-critical real-time systems at a significantly lower cost.

Download or read book Preemptive Scheduling of Parallel Tasks written by International Business Machines Corporation. Research Division and published by . This book was released on 1995 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: "Consider a system of independent parallel tasks which are to be scheduled on a parallel computer. Preemptive execution of the tasks is allowed as long as there is no task migration between the processors, and all subtasks associated with a task are active at the same time. For each task the number of processors, the execution time and a weight are known. The problem is to find a schedule that minimizes the mean weighted flow time. Recently, a polynomial algorithm has been presented for this NP-hard problem which does not allow preemption and produces solutions within a fixed multiplicative constant (10.45) of the optimal non-preemptive schedule. It has also been shown that when all the tasks require only a single processor preemption does not reduce the cost of the optimal schedule. In this paper we show that when tasks run across multiple processors preemption can produce better solutions. We then describe a new algorithm with a bound of approximately 2.42 and show that this bound is tight for the algorithm. An interesting feature of our method is that it requires that at most two tasks be resident at any time on a given processor."

Download or read book Scheduling for Parallel Processing written by Maciej Drozdowski and published by Springer Science & Business Media. This book was released on 2010-03-14 with total page 395 pages. Available in PDF, EPUB and Kindle. Book excerpt: Overview and Goals This book is dedicated to scheduling for parallel processing. Presenting a research ?eld as broad as this one poses considerable dif?culties. Scheduling for parallel computing is an interdisciplinary subject joining many ?elds of science and te- nology. Thus, to understand the scheduling problems and the methods of solving them it is necessary to know the limitations in related areas. Another dif?culty is that the subject of scheduling parallel computations is immense. Even simple search in bibliographical databases reveals thousands of publications on this topic. The - versity in understanding scheduling problems is so great that it seems impossible to juxtapose them in one scheduling taxonomy. Therefore, most of the papers on scheduling for parallel processing refer to one scheduling problem resulting from one way of perceiving the reality. Only a few publications attempt to arrange this ?eld of knowledge systematically. In this book we will follow two guidelines. One guideline is a distinction - tween scheduling models which comprise a set of scheduling problems solved by dedicated algorithms. Thus, the aim of this book is to present scheduling models for parallel processing, problems de?ned on the grounds of certain scheduling models, and algorithms solving the scheduling problems. Most of the scheduling problems are combinatorial in nature. Therefore, the second guideline is the methodology of computational complexity theory. Inthisbookwepresentfourexamplesofschedulingmodels. Wewillgodeepinto the models, problems, and algorithms so that after acquiring some understanding of them we will attempt to draw conclusions on their mutual relationships.

Download or read book Approximation Algorithms for Multi processor Task Scheduling Problems on Identical Parallel Processors written by Saber Khakpash and published by . This book was released on 2013 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis we present approximation algorithms for some multi-processor task scheduling problems. In a scheduling problem, there is a set of processors P that can be used to process a set of tasks T and the goal is to find a feasible scheduling of the tasks on the processors, while optimizing an objective function. In a multi-processor task scheduling problem, tasks can be executed on several processors simultaneously. In scheduling problems, tasks can be preemptive or non-preemptive. Preemptive tasks can be interrupted during their execution and resumed later with no cost. In contrast, a non-preemptive task cannot be interrupted during its execution. In Chapter 2 we propose polynomial time algorithms using linear programming to solve the preemptive scheduling problems for minimizing the maximum completion time, the maximum latency, and the maximum flow time. In Chapter 3 we consider two non-preemptive scheduling problems: the problem of minimizing the maximum completion time when tasks have minimum degree of parallelism, and problem of minimizing the maximum flow time. In Chapter 4 we consider online scheduling of multi-processor tasks with minimum degree of parallelism. In online scheduling, the scheduler does not have access to the entire input instance initially and the scheduler will have access to tasks' characteristics over time. We show that it is not possible for an online scheduler to find a feasible scheduling for all input instances of the problem. We propose a bicriteria (O(log m),1)-approximation algorithm for the problem.

Download or read book Scheduling Parallel Real time Tasks that Allow Imprecise Results written by Albert Chuang-Shi Yu and published by . This book was released on 1992 with total page 284 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scheduling Tasks with Ready Times and Deadlines to Minimize Average Error written by Wei-Kuan Shih and published by . This book was released on 1989 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Memory Efficient Scheduling for Multicore Real time Systems written by Ahmed Alhammad and published by . This book was released on 2016 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: Modern real-time systems are becoming increasingly complex and requiring significant computational power to meet their demands. Since the increase in uniprocessor speed has slowed down in the last decade, multicore processors are now the preferred way to supply the increased performance demand of real-time systems. A significant amount of work in the real-time community has focused on scheduling solutions for multicore processors for both sequential and parallel real-time tasks. Even though such solutions are able to provide strict timing guarantees on the overall response time of real-time tasks, they rely on the assumption that the worst-case execution time (WCET) of each individual task is known. However, physical shared resources such as main memory and I/O are heavily employed in multicore processors. These resources are limited and therefore subject to contention. In fact, the execution time of one task when run in parallel with other tasks is significantly larger than the execution time of the same task when run in isolation. In addition, the presence of shared resources increases the timing unpredictability due to the conflicts generated by multiple cores. As a result, the adoption of multicore processors for real-time systems is dependent upon solving such sources of unpredictability. In this dissertation, we investigate memory bus contention. In particular, two main problems are associated with memory contention: (1) unpredictable behavior and (2) hindrance of performance. We show how to mitigate these two problems through scheduling. Scheduling is an attractive tool that can be easily integrated into the system without the need for hardware modifications. We adopt an execution model that exposes memory as a resource to the scheduling algorithm. Thus, the theory of real-time multiprocessor scheduling, that has seen significant advances in recent years, can be utilized to schedule both processor cores and memory. Since the real-time workload on multicore processors can be modeled as sequential or parallel tasks, we also study parallel task scheduling by taking memory time into account.

Download or read book Real time Scheduling Algorithms for Precedence Related Tasks on Heterogeneous Multiprocessors written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The problem of real-time scheduling has been very well researched for the single processor case and the identical multiprocessor case. There are a number of efficient algorithms and schedulability tests that enable the system designer to model his/her application as a set of real-time tasks. However, it may very well be the case that the multiprocessor system consists of processors with different speeds and configurations. This heterogeneity makes the scheduling problem much more complex. Real-time scheduling on heterogeneous multiprocessors has not received much attention in the scheduling literature. We propose several algorithms for scheduling a set of precedence related tasks on heterogeneous multiprocessors. In the first section, we propose a reliability driven algorithm for scheduling periodic tasks on heterogeneous systems. We relax the assumption that all the processors in the system are equally reliable. We introduce a new metric called cost of dependability. The periodic tasks are assigned to processors in such a way that the reliability of the system is maximized. We observe that our scheme generate schedules that are consistently more reliable than the schedules generated by algorithms that do not take the reliability of the processors into account. In the second section, we propose a duplication based algorithm for scheduling a set of soft deadline tasks on a system of heterogeneous multiprocessors. We observe that communicating tasks assigned to different processors have to incur a delay by using the inter-processor communication channel. By duplicating any of these two tasks on either assigned processor, we can cut down on that delay. Hence tasks can start (and hence finish) earlier. This leads to a larger number of tasks meeting their deadlines and hence an increase in the guarantee ratio of the real-time application. The next section extends the concept of task duplication to a set of hard deadline tasks. The deadlines are hard in that even a single deadline miss could lead to catastrophic results. By employing task duplication, we observe that a larger number of task sets are able to finish execution before their deadlines. Hence, the success ratio of the application experiences an increment. Based on our simulation results, we observe that our proposed algorithm offers a higher success ratio as compared to the other algorithms that do not use task duplication. It may very well be the case that the real-time application consists of a mix of tasks with hard and soft deadlines. In the next section, we propose an integrated scheme for scheduling a mix of hard and soft deadline tasks on heterogeneous multiprocessors. We observe that our scheme offers a better schedulability as compared to the other algorithms in the literature when sufficient processors are available and when communication is a dominant factor in the system. Moreover, our algorithm is scalable in that the application can be scheduled even if sufficient processors are not available for the initial cluster generation.

Download or read book On line Hard Real time Scheduling of Parallel Tasks on Partitionable Multiprocessors written by Davender Babbar and published by . This book was released on 1994 with total page 418 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Love for Association Fodbold Udg af Dansk Boldspil Union written by and published by . This book was released on 1899 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Multiprocessor Scheduling of Mixed Criticality Parallel Systems written by Guangdong Liu and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Motivated by the increasing trend in embedded systems towards platform integration, there has been an increasing research interest in scheduling mixed-criticality (MC) systems. However, most existing efforts have concentrated on scheduling sequential mixed-criticality tasks and ignored intra-task parallelism. As MC systems are increasingly being implemented on multiprocessor platforms, it is important to take advantage of intra-task parallelism in order to accommodate tasks with higher execution demands and tighter deadlines, such as those used in autonomous vehicles, video processing, radar tracking and robotic systems.

Download or read book Parallel Real time Scheduling for Latency critical Applications written by Jing Li (Computer scientist) and published by . This book was released on 2017 with total page 337 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to provide safety guarantees or quality of service guarantees, many of today's systems consist of latency-critical applications, e.g. applications with timing constraints. The problem of scheduling multiple latency-critical jobs on a multiprocessor or multicore machine has been extensively studied for sequential (non-parallizable) jobs and different system models and different objectives have been considered. However, the computational requirement of a single job is still limited by the capacity of a single core. To provide increasingly complex functionalities of applications and to complete their higher computational demands within the same or even more stringent timing constraints, we must exploit the internal parallelism of jobs, where individual jobs are parallel programs and can potentially utilize more than one core in parallel. However, there is little work considering scheduling multiple parallel jobs that are latency-critical. This dissertation focuses on developing new scheduling strategies, analysis tools, and practical platform design techniques to enable efficient and scalable parallel real-time scheduling for latency-critical applications on multicore systems. In particular, the research is focused on two types of systems: (1) static real-time systems for tasks with deadlines where the temporal properties of the tasks that need to execute is known a priori and the goal is to guarantee the temporal correctness of the tasks prior to their executions; and (2) online systems for latency-critical jobs where multiple jobs arrive over time and the goal to optimize for a performance objective of jobs during the execution. For static real-time systems for parallel tasks, several scheduling strategies, including global earliest deadline first, global rate monotonic and a novel federated scheduling, are proposed, analyzed and implemented. These scheduling strategies have the best known theoretical performance for parallel real-time tasks under any global strategy, any fixed priority scheduling and any scheduling strategy, respectively. In addition, federated scheduling is generalized to systems with multiple criticality levels and systems with stochastic tasks. Both numerical and empirical experiments show that federated scheduling and its variations have good schedulability performance and are efficient in practice. For online systems with multiple latency-critical jobs, different online scheduling strategies are proposed and analyzed for different objectives, including maximizing the number of jobs meeting a target latency, maximizing the profit of jobs, minimizing the maximum latency and minimizing the average latency. For example, a simple First-In-First-Out scheduler is proven to be scalable for minimizing the maximum latency. Based on this theoretical intuition, a more practical work-stealing scheduler is developed, analyzed and implemented. Empirical evaluations indicate that, on both real world and synthetic workloads, this work-stealing implementation performs almost as well as an optimal scheduler.

Download or read book Real time Systems Scheduling 2 written by Maryline Chetto and published by John Wiley & Sons. This book was released on 2014-09-10 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt: Real-time systems are used in a wide range of applications, including control, sensing, multimedia, etc. Scheduling is a central problem for these computing/communication systems since it is responsible for software execution in a timely manner. This book, the second of two volumes on the subject, brings together knowledge on specific topics and discusses the recent advances for some of them. It addresses foundations as well as the latest advances and findings in real-time scheduling, giving comprehensive references to important papers, but the chapters are short and not overloaded with confusing details. Coverage includes scheduling approaches for networks and for energy autonomous systems. Other sophisticated issues, such as feedback control scheduling and probabilistic scheduling, are also addressed. This book can serve as a textbook for courses on the topic in bachelor's degrees and in more advanced master's degree programs. It also provides a reference for computer scientists and engineers involved in the design or the development of Cyber-Physical Systems which require up-to-date real-time scheduling solutions.

Download or read book Scheduling Parallelizable Tasks to Minimize Average Response Time written by International Business Machines Corporation. Research Division and published by . This book was released on 1994 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: "A parallelizable (or malleable) task is one which can be run on an arbitrary number of processors, with a task execution time that depends on the number of processors allotted to it. Consider a system of M independent parallelizable tasks which are to be scheduled without preemption on a parallel computer consisting of P identical processors. For each task, the execution time is a known function of the number of processors allotted to it. The goal is to find (1) for each task i, an allotment of processors [beta][subscript i], and (2) overall, a non-preemptive schedule assigning the tasks to the processors which minimizes the average response time of the tasks. Equivalently, we can minimize the flow time, which is the sum of the completion times of each of the tasks. In this paper we tackle the problem of finding a schedule with minimum average response time in the special case where each task in the system has sublinear speedup. This natural restriction on the task execution time means simply that the efficiency of a task decreases or remains constant as the number of processors allotted to it increases. The scheduling problem with sublinear speedups has been shown to be NP-complete in the strong sense. We therefore focus on finding a polynomial time algorithm whose solution comes within a fixed multiplicative constant of optimal. In particular, we give an algorithm which finds a schedule having a response time that is within 2 times that of the optimal schedule and which runs in O(M(M2 + P)) time."

Download or read book Non preemptive Scheduling of Unequal Execution Time Tasks on Two Identical Processors written by D. Goyal and published by . This book was released on 1977 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scheduling in Real Time Systems written by Francis Cottet and published by Wiley. This book was released on 2002-11-22 with total page 282 pages. Available in PDF, EPUB and Kindle. Book excerpt: * Real-time systems are used in a wide range of applications, including command and control systems, flight control, telecommunication systems, and online purchase payment * Provides an accessible yet comprehensive treatment * of real-time computing and communications systems * Outlines the basics of real-time scheduling and scheduling policies designed for real-time applications * Each chapter contains examples and case studies along with test exercises and solutions