scholarly journals Online Slack-Stealing Scheduling with Modified laEDF in Real-Time Systems

Electronics ◽  
2019 ◽  
Vol 8 (11) ◽  
pp. 1286 ◽  
Author(s):  
Wonbo Jeon ◽  
Wonsop Kim ◽  
Heoncheol Lee ◽  
Cheol-Hoon Lee
Keyword(s):  
Response Time ◽  
Real Time ◽  
Execution Time ◽  
Computation Method ◽  
Periodic Tasks ◽  
Worst Case ◽  
Dynamic Priority ◽  
Look Ahead ◽  
Aperiodic Tasks ◽  
Hard Real Time

In hard real-time task systems where periodic and aperiodic tasks coexist, the object of task scheduling is to reduce the response time of the aperiodic tasks while meeting the deadline of periodic tasks. Total bandwidth server (TBS) and advanced TBS (ATBS) are used in dynamic priority systems. However, these methods are not optimal solutions because they use the worst-case execution time (WCET) or the estimation value of the actual execution time of the aperiodic tasks. This paper presents an online slack-stealing algorithm called SSML that can make significant response time reducing by modification of look-ahead earliest deadline first (laEDF) algorithm as the slack computation method. While the conventional slack-stealing method has a disadvantage that the slack amount of each frame must be calculated in advance, SSML calculates the slack when aperiodic tasks arrive. Our simulation results show that SSML outperforms the existing TBS based algorithms when the periodic task utilization is higher than 60%. Compared to ATBS with virtual release advancing (VRA), the proposed algorithm can reduce the response time up to about 75%. The performance advantage becomes much larger as the utilization increases. Moreover, it shows a small performance variation of response time for various task environments.

Scheduling of Aperiodic Tasks on Multicore Systems

2020 ◽  
pp. 14-35
Author(s):  
Shruti Jadon ◽  
Rama Shankar Yadav
Keyword(s):  
Response Time ◽  
Real Time ◽  
Multicore Systems ◽  
Multicore Processor ◽  
Periodic Tasks ◽  
Aperiodic Tasks ◽  
Multicore System ◽  
Hard Real Time ◽  
Work Done ◽  
Aperiodic Task

For a hard real-time multicore system, the two important issues that are required to be addressed are feasibility of a task set and balancing of load amongst the cores of the multicore systems. Most of the previous work done considers the scheduling of periodic tasks on a multicore system. This chapter deals with scheduling of aperiodic tasks on a multicore system in a hard real-time environment. In this regard, a multicore total bandwidth server (MTBS) is proposed which schedules the aperiodic tasks with already guaranteed periodic tasks amongst the cores of the multicore processor. The proposed MTBS algorithm works by computing a virtual deadline for every aperiodic task that is arriving to the system. Apart from schedulability of aperiodic tasks, the MTBS approach also focuses on reducing the response time of aperiodic tasks. The simulation studies of MTBS were carried out to find the effectiveness of the proposed approach, and it is also compared with the existing strategies.

scholarly journals Dynamic approach to minimize overhead and response time in scheduling periodic real-time tasks

2021 ◽  
Vol 8 (4) ◽  
pp. 75-81
Author(s):  
Ahmed A. Alsheikhy ◽  
Keyword(s):  
Response Time ◽  
Real Time ◽  
Periodic Tasks ◽  
Dynamic Priority ◽  
New Novel ◽  
Context Switching ◽  
Novel Approach ◽  
Efficiency And Effectiveness ◽  
Time Systems ◽  
The Given

In real-time systems, a task or a set of tasks needs to be executed and completed successfully within a predefined time. Those systems require a scheduling technique or a set of scheduling methods to distribute the given task or the set of tasks among different processors or on a processor. In this paper, a new novel scheduling approach to minimize the overhead from context switching between several periodic tasks is presented. This method speeds up a required response time while ensuring that all tasks meet their deadline times and there is no deadline miss occurred. It is a dynamic-priority technique that works either on a uniprocessor or several processors. In particular, it is proposed to be applied on multiprocessor environments since many applications run on several processors. Various examples are presented within this paper to demonstrate its optimality and efficiency. In addition, several comparison experiments with an earlier version of this approach were performed to demonstrate its efficiency and effectiveness too. Those experiments showed that this novel approach sped up the execution time from 15% to nearly around 46%. In addition, it proved that it reduced the number of a context switch between tasks from 12% to around 50% as shown from simulation tests. Furthermore, this approach delivered all tasks/jobs successfully and ensured there was no deadline miss happened.

scholarly journals Scheduling an aperiodic flow within a real-time system using Fairness properties

2014 ◽  
Vol Volume 18, 2014 ◽  
Author(s):  
Annie Choquet-Geniet ◽  
Sadouanouan MALO
Keyword(s):  
Real Time ◽  
Acceptance Test ◽  
Periodic Tasks ◽  
Real Time System ◽  
Model Driven ◽  
Aperiodic Tasks ◽  
International Audience ◽  
Hard Real Time ◽  
Model Driven Approach ◽  
Time Systems

International audience We consider hard real-time systems composed of periodic tasks and of an aperiodic flow. Each task, either periodic or aperiodic, has a firm deadline. An aperiodic task is accepted within the system only if it can be completed before its deadline, without causing temporal failures for the periodic tasks or for the previously accepted aperiodic tasks. We propose an acceptance test, linear in the number of pending accepted aperiodic tasks. This protocol can be used provided the idle slots left by the periodic tasks are fairly distributed. We then propose a model-driven approach, based on Petri nets, to produce schedules with a fair distribution of the idle slots for systems of non independent periodic tasks. Nous considérons des systèmes temps-réel composés de tâches périodiques et d’un fluxapériodique. Toutes les tâches, périodiques comme apériodiques, sont soumises à des échéancesstrictes. Une tâche apériodique n’est acceptée que si elle ne remet pas en cause le respect deséchéances par les tâches périodiques et par les tâches apériodiques déjà acceptées. Nous proposonsun protocole d’acceptation des tâches apériodiques de complexité linéaire en le nombre de tâchesapériodiques acceptées présentes dans le système. Ce protocle est utilisable dès lors que les tempscreux sont répartis de manière équitable. Nous proposons donc une approche modèle, à base deréseaux de Petri, pour produire des séquences où les temps creux sont équitablement répartis, pourdes systèmes de tâches interdépendantes.

An Overview of Worst-Case Execution Time Estimation for Embedded Programs

2014 ◽  
Vol 651-653 ◽  
pp. 624-629
Author(s):  
Liang Liang Kong ◽  
Lin Xiang Shi ◽  
Lin Chen
Keyword(s):  
Embedded Systems ◽  
Real Time ◽  
Execution Time ◽  
Time Estimation ◽  
Worst Case ◽  
Performance Metric ◽  
Worst Case Execution Time ◽  
Hard Real Time ◽  
Time Systems

Most embedded systems are real-time systems, so real-time is an important performance metric for embedded systems. The worst-case execution time (WCET) estimation for embedded programs could satisfy the requirement of hard real-time evaluation, so it is widely used in embedded systems evaluation. Based on sufficient survey on the progress of WCET estimation around the world, it proposes a new classification of WCET estimation. After introducing the principle of WCET estimation, it mainly demonstrates various types of technologies to estimate WCET and classifies them into two main streams, namely, static and dynamic WCET estimations. Finally, it shows the development of WCET analysis tools.

New Optimal Preemptively Scheduling for Real-Time Reconfigurable Sporadic Tasks Based on Earliest Deadline First Algorithm

2012 ◽  
Vol 4 (2) ◽  
pp. 65-81 ◽  
Author(s):  
Hamza Gharsellaoui ◽  
Mohamed Khalgui ◽  
Samir Ben Ahmed
Keyword(s):  
Response Time ◽  
Real Time ◽  
Dynamic Scheduling ◽  
Optimal Algorithm ◽  
Real Life ◽  
Sporadic Tasks ◽  
Periodic Tasks ◽  
Worst Case ◽  
Utilization Factor ◽  
Earliest Deadline

This paper examines the problem of scheduling the mixed workload of both sporadic (on-line) and periodic (off-line) tasks on uniprocessor in a hard real-time environment. The authors introduce an optimal earliest deadline scheduling algorithm to optimize response time while ensuring that all periodic tasks meet their deadlines and to accept as many sporadic tasks. A necessary and sufficient schedulability test is presented, and an efficient O(n+m) guarantee algorithm is proposed. This optimal algorithm results in dynamic scheduling solutions. They are presented by a proposed intelligent agent-based architecture where a software agent is used to evaluate the response time, to calculate the processor utilization factor and also to verify the satisfaction of real-time deadlines. The agent dynamically provides technical solutions for users where the system becomes unfeasible by sending sporadic tasks to idle times, by modifying the deadlines of tasks, the worst case execution times (WCETs), the activation time, by tolerating some non critical tasks according to the (m, n) firm and a reasonable cost, or in the worst case by removing some non hard (soft) tasks according to predefined heuristic. The authors implement the agent to support these services which are applied to extensive experiments with real-life design examples in order to demonstrate the effectiveness and the excellent performance of the new optimal algorithm in normal and overload conditions.

The Algorithms of Dynamic Servers for Scheduling Aperiodic Real-Time Tasks – A Review

2014 ◽  
Vol 945-949 ◽  
pp. 3380-3383
Author(s):  
Feng Xiang Zhang
Keyword(s):  
Embedded Systems ◽  
Real Time ◽  
Schedulability Analysis ◽  
Periodic Tasks ◽  
Dynamic Algorithms ◽  
Fixed Priority ◽  
Aperiodic Tasks ◽  
Hard Real Time

This paper focus on the dynamic server algorithms, and the servers are used for scheduling soft aperiodic tasks. Many types of servers and their schedulability analysis are reviewed, these properties can be used for constructing hierarchical embedded systems, where the soft aperiodic tasks and the hard real-time tasks can be scheduled in the same system. The aperiodic tasks in the server are not preemptable, and they are executed in a first-come first-served (FCFS) manner. If it is not specified, there is only one server in the system, and rest of the processes in the system are ordinary periodic tasks. The servers could be scheduled by fixed priority or dynamic algorithms.

scholarly journals Phasing of Periodic Tasks Distributed over Real-time Fieldbus

2017 ◽  
Vol 12 (5) ◽  
pp. 645 ◽  
Author(s):  
Sang-Hun Lee ◽  
Hyun-Wook Jin ◽  
Kanghee Kim ◽  
Sangil Lee
Keyword(s):  
Real Time ◽  
Search Time ◽  
Periodic Tasks ◽  
Worst Case ◽  
Real Time System ◽  
Delay Bound ◽  
End To End Delay ◽  
Global Clock ◽  
End To End ◽  
Hard Real Time

In designing a distributed hard real-time system, it is important to reduce the end-to-end delay of each real-time message in order to ensure quick responses to external inputs and a high degree of synchronization among cooperating actuators. In order to provide a real-time guarantee for each message, the related literature has focused on the analysis of end-to-end delays based on worst-case task phasing. However, such analyses are too pessimistic because they do not assume a global clock. With the assumption that task phases can be managed by using a global clock provided by emerging real-time fieldbuses, such as EtherCAT, we can try to calculate the optimal task phasing that yields the minimal worst-case end-to-end delay. In this study, we propose a heuristic to manage the phase offsets in the distributed tasks to reduce the theoretical end-to-end delay bound. The proposed heuristic reduces the search time for a solution by identifying time intervals where actual communication occurs among inter-dependent tasks. Furthermore, to analyze the distribution of endto- end delays in different phases, we implemented a simulation tool. The simulation results showed that the proposed heuristic can reduce worst-case end-to-end delay as well as jitter in end-to-end delays.

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