Total Bandwidth Server Research Articles

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

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.

A Migration Aware Scheduling Technique for Real-Time Aperiodic Tasks Over Multiprocessor Systems

Multi-processor systems consist of more than one processor and are mostly used for computationally intensive applications. Real-time systems are those systems that require completing execution of tasks within a pre-defined deadline. Traditionally, multiprocessor systems are given attention in periodic models, where tasks are executed at regular intervals of time. Gradually, as maturity in a multiprocessor design had increased; their usage has become very common for real-time systems to execute both periodic and aperiodic tasks. As the priority of an aperiodic task is usually but not essentially greater than the priority of a periodic task, they must be completed within the deadline. There is a lot of research works on multiprocessor systems with scheduling of periodic tasks, but the task scheduling is relatively remained unexplored for a mixed workload of both periodic and aperiodic tasks. Moreover, higher energy consumption is another main issue in multiprocessor systems. Although it could be reduced by using the energy-aware scheduling technique, the response time of aperiodic tasks still increases. In the literature, various techniques were suggested to decrease the energy consumption of these systems. However, the study on reducing the response time of aperiodic tasks is limited. In this paper, we propose a scheduling technique that: 1) executes aperiodic tasks at full speed and migrates periodic tasks to other processors if their deadline is earlier than aperiodic tasks-reduces the response time and 2) executes aperiodic tasks with lower speed by identifying appropriate processor speed without affecting the response time-reduces energy consumption. Through simulations, we demonstrate the efficiency of the proposed algorithm and we show that our algorithm also outperforms the well-known total bandwidth server algorithm.

Enhanced virtual release advancing algorithm for real-time task scheduling

ABSTRACTIn real-time task scheduling, response time and time complexity are two of important requirements that draw many attentions. Virtual release advancing (VRA) [Tanaka, K. (2015, June). Virtual release advancing for earlier deadlines. ACM SIGBED Review, 12(3), 28–31] is an effective technique for shorter response times in the Earliest Deadline First scheduling [Liu, C. L., & Layland, J. W. (1973). Scheduling algorithms for multiprogramming in a hard-real-time environment. Journal of the Association for Computing Machinery, 20(1), 46–61], but not adaptive to precise systems due to its high time complexity. In order to mitigate the time complexity, a new technique, called enhanced VRA, is presented in this paper. Applied to the Total Bandwidth Server context, the enhanced technique significantly improves the time complexity while guaranteeing the responsiveness and schedulability. The technique is implemented on an ITRON real-time operating system running on an ARM Cortex-A9 processing core with a field programmable gate array. With supporting of accelerator hardware, the new algorithm shows that the maximum additional runtime overhead per tick is reduced by up to 30% compared with that of the original (software) VRA.

Virtual release advancing for earlier deadlines

Giving tasks more urgent deadlines leads to shorter response times in EDF-based scheduling. This paper describes a technique that gives earlier deadlines by virtually advancing release times in the Total Bandwidth Server (TBS) context. This technique improves aperiodic tasks' responsiveness while it guarantees the schedulability of the system. Simulations show the technique outperforms TBS and its enhanced one.

A Hierarchical Scheme for Open System Environments Review

This paper focus on hierarchical scheduling for real-time applications for open embedded system environments constructed by the total bandwidth server, according to its algorithms, when a job at the head of the server's ready queue completes, the server budget is replenished immediately if the ready queue is not empty. This paper gives some examples to the solutions proposed by Deng et al for a two-level hierarchical scheduling model in which the global level of the system is earliest deadline first, and the local scheduler could be any algorithm. The scheduling algorithms and schedulability analysis for the tasks are reviewed in an open system where the applications could be modeled as executing on a slow processor.

Schedulability Criteria and Analysis for Dynamic and Flexible Resource Management

The Flexible Resource Manager (FRM) is a dynamic resource management approach that allows a better utilization of the available resources. However, it necessitates an atomic reconfiguration process that must not violate hard timing constraints. This paper exploits the deadline assignment rule of the Total Bandwidth Server (TBS) to schedule reconfiguration, and it formally shows that there exists a minimum task period for which atomicity and schedulability can be guaranteed. With this solution, real-time system engineers have the tools at hand to design their tasks to exploit the benefits of the FRM with hard real-time constraints.11This work was developed in the course of the Collaborative Research Center 614 - Self-Optimizing Concepts and Structures in Mechanical Engineering - Paderborn University, and was published on its behalf and funded by the Deutsche Forschungsgemeinschaft.

Feedback-Controlled Server for Scheduling Aperiodic Tasks

This paper proposes a scheduling scheme using feedback control to reduce the response time of aperiodic tasks with soft real-time constraints. We design an algorithm based on the proposed scheduling scheme and Total Bandwidth Server (TBS) that is a conventional server technique for scheduling aperiodic tasks. We then describe the feedback controller of the algorithm and give the control parameter tuning methods. The simulation study demonstrates that the algorithm can reduce the mean response time up to 26% compared to TBS in exchange for slight deadline misses. Keywords—Real-Time Systems, Aperiodic Task Scheduling, Feedback-Control Scheduling, Total Bandwidth Server

Optimal deadline assignment for scheduling soft aperiodic tasks in hard real-time environments

We present a novel scheduling approach for servicing soft aperiodic requests in a hard real time environment, where a set of hard periodic tasks is scheduled using the Earliest Deadline First algorithm. The main characteristic of the proposed algorithm is that it achieves full processor utilization and optimal aperiodic responsiveness, still guaranteeing the execution of the periodic tasks. Another interesting feature of the proposed algorithm is that it can easily be tuned to balance performance versus complexity for adapting it to different application requirements. Schedulability issues, performance results, and implementation complexity of the algorithm are discussed and compared with other methods, such as Background, the Total Bandwidth Server, and the Slack Stealer. Resource reclaiming and extensions to more general cases are also considered. Extensive simulations show that a substantial improvement can be achieved with a little increase of complexity, ranging from the performance of the Total Bandwidth Server up to the optimal behavior.