An Efficient Real-Time Multiprocessor Scheduling Algorithm

1998

In a parallelizable task model, a task can be parallelized and the component tasks can be executed concurrently on multiple processors. We use this parallelism in tasks to meet their deadlines and also obtain better processor utilisation compared to non-parallelized tasks. Non-preemptive parallelizable task scheduling combines the advantages of higher schedulability and lower scheduling overhead o ered by the preemptive and non-preemptive task scheduling models, respectively. We propose a new approach to maximize the bene ts from task parallelization. It involves checking the schedulability of periodic tasks (if necessary, by parallelizing them) o-line and run-time scheduling of the schedulable periodic tasks together with dynamically arriving aperiodic tasks. To avoid the run-time anomaly that may occur when the actual computation time of a task is less than its worst case computation time, we propose e cient run-time mechanisms. We have carried out extensive simulation to study the e ectiveness of the proposed approach by comparing the schedulability o ered by it with that of dynamic scheduling using Earliest Deadline First (EDF), and by comparing its storage e ciency with that of the static table-driven approach. We found that the schedulability o ered by parallelizable task scheduling is always higher than that of the EDF algorithm for a wide variety of task parameters and the storage overhead incurred by it is less than 3.6% of the static table-driven approach even under heavy task loads.

Real-Time systems are becoming pervasive. In a Real-Time System the correctness of the system behavior depends not only on the logical results of the computations, but also on the physical instant at which these results are produced. A missed deadline in hard real-time systems is catastrophic and in soft real-time systems it can lead to a significant loss .This work talks about static and dynamic scheduling algorithms for real time task. The problem of real-time scheduling spans a broad spectrum of algorithms from simple uniprocessor to highly sophisticated multiprocessor scheduling algorithms which are priority driven and divided into three classes fixed priority, dynamic priority and hybrid priority. Finally conclusion shows that Instantaneous utilization factor scheduling Algorithm gives better result in uniprocessor scheduling algorithms and Modified Instantaneous utilization factor scheduling Algorithm gives better context switching, response time and CPU utilization as compared to previous scheduling algorithms.

2011

Real-time scheduling is one of the most important aspects of a real-time system design. To achieve a real-time system’s requirement, especially to be fast, multiprocessor systems are used. Generally, multiprocessor real-time scheduling algorithms fall into one the two well-known approaches: Partitioning or Global. The partitioning approach has acceptable overhead for underlying system but can NOT guarantee to provide an optimal schedule. The global approach can provide this guarantee by holding some preconditions and considerable overheads. In this paper, an intermediate hybrid multiprocessor realtime scheduling approach is proposed in which optimality will be reached via the minimum overheads for underlying system. Presenting and analyzing different feasible paradigms for combination of the two existing approaches, the proposed hybrid approach satisfies the two major goals of this combination: optimality and lightweightness. Experimental results show that the hybrid approach outper...

2013 IEEE 34th Real-Time Systems Symposium, 2013

We present HIME, a new EDF-based semi-partitioned scheduling algorithm which allows at most one migrating task per processor. In a system with m processors, this arrangement limits the migrating tasks to at most m/2 and the number of migrations per job to at most m-1. HIME has a utilisation bound of at least 74.9%, and can be configured to achieve 75%, the theoretical limit for semi-partitioned schemes with at most m/2 migrating tasks. Experiments show that the average system utilisation achieved by HIME is about 95%.

2007 International Symposium on Industrial Embedded Systems, 2007

We present an optimal real-time scheduling algorithm for multiprocessors-one that satisfies all task deadlines, when the total utilization demand does not exceed the utilization capacity of the processors. The algorithm called LLREF, is designed based on a novel abstraction for reasoning about task execution behavior on multiprocessors: the Time and Local Execution Time Domain Plane (or T-L plane). LLREF is based on the fluid scheduling model and the fairness notion, and uses the T-L plane to describe fluid schedules without using time quanta, unlike the optimal Pfair algorithm (which uses time quanta). We show that scheduling for multiprocessors can be viewed as repeatedly occurring T-L planes, and feasibly scheduling on a single T-L plane results in the optimal schedule. We analytically establish the optimality of LLREF. Further, we establish that the algorithm has bounded overhead, and this bound is independent of time quanta (unlike Pfair). Our simulation results validate our analysis on the algorithm overhead.

Imprecise computation model is used in dynamic scheduling algorithm having heuristic function to schedule task sets. A task is characterized by ready time, worst case computation time, deadline and resource requirements. A task failing to meet its deadline and resource requirements on time is split into mandatory part and optional part. These sub-tasks of a task can execute concurrently on multiple cores, thus achieving parallelization provided by the multi-core system. Mandatory part produces acceptable results while optional part refines the result further. To study the effectiveness of proposed scheduling algorithm, extensive simulation studies have been carried out. Performance of proposed scheduling algorithm is compared with myopic and improved myopic scheduling algorithm. The simulation studies shows that schedulability of task split myopic algorithm is always higher than myopic and improved myopic algorithm.

MATEC Web of Conferences, 2019

Generally, multiprocessor real-time scheduling algorithm fall into two basic approaches, partitioned and global. The hybrid solution that we proposed applies the partitioned scheduling approach to the task set until all processors have been filled. The remaining tasks are then scheduled using the global scheduling approach. The idea of a hybrid scheduling approach to ameliorate limitations of partitioned and global approaches. Studies have shown that most prior research on hybrid multiprocessor real-time scheduling has been confined to hard and soft real-time tasks. In fact, the implementation of hybrid approach and the performance of such algorithms in comparison to partitioned and global approaches have not been fully answered by previous studies. This paper performs experimental evaluation of our proposed hybrid multiprocessor scheduling approach, R-BOUND-MP-NFRNS and RM-US (m/3m-2) with multiprocessor response time test, with one of the best scheduling approach from partitioned ...

2011

Optimal multiprocessor real-time schedulers incur significant overhead for preemptions and migrations. We present RUN, an efficient scheduler that reduces the multiprocessor problem to a series of uniprocessor problems. RUN significantly outperforms existing optimal algorithms with an upper bound of O(log m) average preemptions per job on m processors (≤ than 3 per job in all of our simulated task sets) and reduces to Partitioned EDF whenever a proper partitioning is found.

Journal of Software, 2010

This paper proposes a hybrid scheduling approach for real-time system on homogeneous multi-core architecture. To make the best of the available parallelism in these systems, first an application is partitioned into some parallel tasks as much as possible. Then the parallel tasks are dispatched to different cores, so as to execute in parallel. In each core, real-time tasks can run concurrently with nonreal-time tasks. The hybrid scheduling approach uses a twolevel scheduling scheme. At the top level, a sporadic server is assigned to each scheduling policy. Each sporadic server is used to schedule the dispatched tasks according to its scheduling policy. At the bottom level, a rate-monotonic OS scheduler is adopted to maintain and schedule the top level sporadic servers. The schedulability test is also considered in this paper. The experimental results show that the hybrid scheme is an efficient scheduling scheme.

Control Engineering Practice, 1997

This paper analyzes the behavior and performance of four dynamic algorithms for multiprocessor scheduling of hard real-time tasks. The well known algorithms are the Earliest Deadline First (EDF) algorithm and the Least Laxity First (LLF) algorithm. An important feature of the original ones is that they are guarantee-oriented. The performance of these algorithms has been measured through simulations which analyze the behavior of the algorithms under two main load hypothesis: static load and dynamic load. Simulation results present practical bounds and a comparative study on the loads that they are able to guarantee, context switches and cpu utilization.