SCHEDULING ALGORITHMS OF REAL TIME SYSTEM AN OVERVIEW

Scheduling of real time tasks are very important aspect in systems as processes should complete its task at a specific time. There is a need of high energy efficiency and low response time in large data stream so for this energy efficient resources and optimized frameworks are needed. Both hard real time and mixed critically systems are targeted. Soft deadline can be handled while hard deadlines are difficult to cater. Different algorithms are used to schedule tasks like rate monotonic, earliest deadline first, deadline monotonic etc.

International Journal of Smart Home, 2015

Now a days Jobs are Scheduled in a single processor or more than one processor, a real time job is scheduled or executed based on requirements, An Successful task in embedded system ought to have constrained asset necessities: Memory, execution time and power utilization, these necessity are not generally simple to fulfil in real-time embedded system with hard task deadlines. In this paper we explore the effective time utilization, without influencing the deadline requirements of typical hard real time task ,there are no limitation on the new results each task can be periodic or sporadic ,with relative deadline which can be less than ,equivalent to or greater than its period, it is too fast , best-effort ,effective real time scheduling algorithm for a wide variety of job parameters.

IEEE Transactions on Parallel and Distributed Systems, 1998

Many time-critical applications require predictable performance and tasks in these applications have deadlines to be met. In this paper, we propose an efficient algorithm for nonpreemptive scheduling of dynamically arriving real-time tasks (aperiodic tasks) in multiprocessor systems. A real-time task is characterized by its deadline, resource requirements, and worst case computation time on p processors, where p is the degree of parallelization of the task. We use this parallelism in tasks to meet their deadlines and, thus, obtain better schedulability compared to nonparallelizable task scheduling algorithms. To study the effectiveness of the proposed scheduling algorithm, we have conducted extensive simulation studies and compared its performance with the myopic [8] scheduling algorithm. The simulation studies show that the schedulability of the proposed algorithm is always higher than that of the myopic algorithm for a wide variety of task parameters.

2002

Real-time systems play an important role in our modern society. They are used in critical control systems that rely on timely response and computed results to function properly. This paper summarizes to an extent the state of real-time systems in the area of scheduling. A vast amount of work that has been done in the area of real-time scheduling by both the operations research and the computer science communities. While concerning ourselves with the scheduling requirements and methodologies of a real-time application, we observe that it is fundamentally different from a non time-constrained time-sharing application. The difference arises in the methods used for scheduling the tasks and the system support that is necessary for such an implementation. In this paper, we will consider the various issues that typify real-time scheduling. We discuss two major algorithms that forms a baseline for all scheduling approaches and we present a real-time implementation of such a system. Real-tim...

2003

In this report we present an annotated bibliography of research work relating to real-time scheduling of tasks. Special emphasis is placed on the different off-line and on-line schedulability testing algorithms for hard, firm and soft real-time tasks. Each proposed algorithm is presented and analyzed in terms of asymptotic time and space complexity. Algorithms are critically examined, when there is sufficient information, with respect to pragmatic issues and hidden overheads in implementation. Both fixed-priority and dynamic-priority methods are presented and analyzed.

Scheduling algorithms allow one to decide which threads are given to resource from moment to moment. Various process scheduling algorithms exist and this paper focuses on the scheduling algorithms used for scheduling processes in a multiprogramming system namely First-Come-First-Served (FCFS), Round Robin (RR), Shortest Job First (SJF), Shortest Remaining Time First (SRTF) and Lottery scheduling. Each algorithm has been discussed and a comparison was made on the basis of eight (8) parameters significant in processes scheduling. In fact, compared to other papers, this research made use of more parameters for the analysis. These parameters include CPU utilization, throughput, waiting time, response time, fairness, starvation, predictability and preemption. From this analysis, we showed that there is actually no scheduling algorithm satisfying the conditions of an ideal algorithm and concluded that further studies which improve current scheduling algorithms need to be done.

Most currently existing optimal real-time multiprocessor scheduling algorithms follow the fairness rule, in which all tasks are forced to make progress in their executions proportional to their utilization, to ensure the optimality of the algorithm. However, obeying the fairness rule results in large number of task preemptions and migrations and these highly affect the practicability of the algorithm. In this paper, we present an efficient real-time multiprocessor scheduling algorithm in which the fairness rule is completely relaxed and a semi-greedy algorithm is introduced. In the simulation, the proposed algorithm showed promising results in terms of number of task preemptions and migrations that are very few compared to the current state of the art real-time multiprocessor scheduling algorithms. Although the algorithm can sometimes miss a very few deadlines, we assume that these deadline misses can be tolerated in view of the great reduction of task preemptions and migrations.

2016

In this review paper we are going to introduce the scheduling in the Distributed real-time system. Real-time system is a sort of plan in which we need to perform the task in certain timeframe with a precise result. Whereas in the general system there is no specified deadline. Actually Scheduling means execution of the task according to their properties and scheduling is performed on different processors, one is Uniprocessor and other is Multiprocessor and it can also be performed on the Distributed system. To schedule real-time task in distributed and multiprocessor system consists of two sub problems: Task allocation to processor and scheduling task on single processors. Task assignment can either be static or dynamic. We will discuss different task allocation algorithm for successful execution of the task.

International Journal of Computer Applications, 2015

In this paper, main scheduling algorithms for hard real-time systems (RTSs) have been investigated that include both uni and multi processors schemes. It provides the summary of schedulability analysis and well-known attributes. This paper composed of two parts; first part surveyed the basic hard RTS scheduling algorithms that guarantee the on-time completion of the tasks. Second part contains the different heuristic and partitioned approaches for some specific factors of real-time systems such as energy consumption, dependability, performance, scheduling feasibility and utilization of memory resource. Finally, the analysis and evaluation of the mentioned methods are shown based on the schedulability of task sets and efficiency.

2005

Multiprocessor architecture becomes common on realtime systems as the workload of real-time systems increases. Recently new deadline-based (EDF-based) multiprocessor scheduling algorithms are devised, and comparative studies on the performance of these algorithms are necessary. In this paper, we compare EDZL, a hybrid of EDF and LLF, with other deadline-based scheduling algorithms such as EDF, EDF-US[m/(2m−1)], and fpEDF. We show EDZL schedules all task sets schedulable by EDF. The experimental results show that the number of preemptions of EDZL is comparable to that of EDF and the schedulable utilization bound of EDZL is higher than those of other algorithms we consider.