Non-preemptive Earliest Deadline First Research Articles

Energy-Aware Nonpreemptive Scheduling of Mixed-Criticality Real-Time Task Systems

Energy-aware real-time scheduling for mixed-criticality (MC) systems with different criticality levels has drawn many researchers’ attentions. However, most of the studies focus on the preemptive MC task model and few studies consider the nonpreemptive MC task model, in which all jobs cannot be preempted until completion. In this article, we address the energy minimization problem for MC systems with nonpreemptive dynamic priority scheduling. First, we develop schedulability test of nonpreemptive earliest deadline first (NP-EDF) in single processor MC systems. Second, we extend the results to nonpreemptive earliest deadline first with virtual deadline (NP-EDFVD), which is the first attempt for nonpreemptive dynamic priority scheduling in single processor MC systems. Third, the energy-aware nonpreemptive scheduling algorithm (EANPS) based on NP-EDFVD is proposed to solve the energy minimization problem for MC systems with nonpreemptive dynamic priority scheduling. Finally, an industrial use-case and extensive simulations are used to validate the performance of the proposed algorithm, and the experimental results show that the EANPS algorithm consumes average 25.72% less energy than that of NP-EDFVD.

Limited Non-Preemptive EDF Scheduling for a Real-Time System with Symmetry Multiprocessors

In a real-time system, a series of jobs invoked by each task should finish its execution before its deadline, and EDF (Earliest Deadline First) is one of the most popular scheduling algorithms to meet such timing constraints of a set of given tasks. However, EDF is known to be ineffective in meeting timing constraints for non-preemptive tasks (which disallow any preemption) when the system does not know the future job release patterns of the tasks. In this paper, we develop a scheduling algorithm for a real-time system with a symmetry multiprocessor platform, which requires only limited information about the future job release patterns of a set of non-preemptive tasks, called LCEDF. We then derive its schedulability analysis that provides timing guarantees of the non-preemptive task set on a symmetry multiprocessor platform. Via simulations, we demonstrate the proposed schedulability analysis for LCEDF significantly improves the schedulability performance in meeting timing constraints of a set of non-preemptive tasks up to 20.16%, compared to vanilla non-preemptive EDF.

Non-Preemptive Scheduling for Mixed-Criticality Real-Time Multiprocessor Systems

Real-time scheduling for Mixed-Criticality (MC) systems has received a growing attention as real-time embedded systems accommodate various tasks with different levels of criticality. While many studies have addressed how to guarantee timing requirements for MC systems with uniprocessor and multiprocessors, most of them have focused on supporting preemptive tasks. On the other hand, there have been few studies to address non-preemptive scheduling especially for MC multiprocessor platforms, in which the jobs under execution cannot be preempted by other jobs. In this paper, we develop schedulability tests for non-preemptive scheduling, which is the first attempt for MC multiprocessor systems. To this end, we first generalize an existing NP-EDF (Non-Preemptive Earliest Deadline First) schedulability test developed for single-criticality multiprocessor systems, towards for MC multiprocessor systems. For the generalization, we introduce new timing guarantee techniques for the system transition between two different criticalities, which is one of the key features in MC systems. We next extend the proposed NP-EDF schedulability test towards NP-EDFVD (NP-EDF with Virtual Deadlines) that is specialized for MC systems, and pose a virtual deadline assignment problem. We develop an optimal virtual deadline assignment policy using a control knob of the system-level deadline-reduction parameter and then a suboptimal one for the task-level parameter. Our simulation results demonstrate that the NP-EDFVD schedulability test with the proposed virtual deadline assignment policies finds a number of additional schedulable task sets, which are not schedulable by the NP-EDF schedulability test.

Assessment of nested-parallel task model under real-time scheduling on multi-core processors

Real-time applications contain numerous time-bound parallel tasks with enormous computations. Parallel models, not the sequential models, have the capability to handle intra-task parallelism and accomplish such tasks in a specific time or before. Previous researchers presented the task models for parallel tasks, but not for the nested-parallel tasks. This paper deals with the real-time scheduling of periodic nested-parallel tasks having an implicit deadline on multi-core processors. Initially, an nested-parallel task model is developed. Next, a novel task disintegration technique is studied where the MAM's ratio is defined to categorise the segments. It is theoretically proved that the discussed disintegration technique achieved a speedup factor of 4.30 and 3.40 when the tasks, after disintegration, are scheduled under partitioned deadline monotonic (DM) and global earliest deadline first (EDF) scheduling, respectively. Further, considering the overhead factor (β) for non-preemptive global EDF scheduling, disintegration technique is analysed and achieved a speedup factor of 3.73 (for β = 1). The proposed disintegration technique is assessed through the simulations thereby indicating the adequacy of derived speedup factors.

Performance Optimization Based on Analytical Modeling in a Real-Time System with Constrained Time/Utility Functions

We consider a single-processor firm real-time (FRT) system with exponential interarrival and execution times for jobs with relative deadlines following a general distribution. The scheduling policy of the system is first-come first-served (FCFS) and the capacity of the system is arbitrary. This system is subject to an arbitrary-shaped time/utility function (TUF), which determines the accrued utility of each job according to its completion time. It is considered that the system power consumption at different working states is predetermined for each processor speed. We have proposed an exact analytical method for the calculation of specific performance and power-related measures of the system. The resulting analytical formulations for the performance measures are functions of the processor speed and system capacity. These measures are optimized through appropriate selections of the speed using derivatives and the capacity employing numerical search methods. Some experimental results are presented for different unimodal TUFs in systems with deterministic and exponential relative deadlines. For the latter distribution, the results are compared against similar results obtained through simulation for the nonpreemptive earliest-deadline-first (NP-EDF) scheduling policy. The comparisons show that FCFS is superior to NP-EDF for some measures and TUFs.

Fine-Tuning MAC-Level Protocols for Optimized Real-Time QoS

In distributed real-time systems, meeting the real-time constraints is mandatory, but the satisfaction of other application-dependent criteria is most generally required as well. In particular, networked control systems (NCS) are known to be sensitive to communication delays such as frame response time jitters. Well-known medium access control (MAC) algorithms such as non-preemptive deadline monotonic (NP-DM) or non-preemptive earliest deadline first (NP-EDF) are efficient in terms of bandwidth usage, but they may perform poorly regarding other application-dependent performance criteria. This paper highlights a class of online scheduling policies targeted at scheduling frames at the MAC level, and it provides a schedulability analysis that is valid for all policies within the considered class. As it will be shown, these algorithms are implementable on COTS components (e.g., Controller Area Network controllers) and offer good trade-offs between feasibility and the satisfaction of other application-dependent criteria such as the response time jitter.

An approximation analysis of nonpreemptive EDF scheduling

Due to recent advances in multimedia technology, a real-time capability is needed to a certain extent even in information systems, in addition to control systems. In general, information systems are classified as soft real-time systems, which keep operating even if a deadline is missed. In soft real-time systems, it is more important to provide statistical guarantees (probabilistic analysis) than absolute guarantees (deadline guarantees). In current real-time systems, real-time scheduling such as EDF (Earliest Deadline First) is used to meet timing constraints. EDF scheduling simply assigns higher priorities in the order of earlier deadlines. It can be applied to aperiodic tasks without prior knowledge of their starting times. In this paper, it is assumed that each attribute of the task follows a probabilistic distribution. The system performance when a nonpreemptive EDF scheduling is applied is then mathematically analyzed. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 89(2): 13–23, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20177

A quasi-static retrieval scheme for interactive VOD servers

Video-on-demand (VOD) servers need to be efficiently designed in order to support a large number of users viewing the same or different videos at different rates. In this paper, we propose a simple quasi-static retrieval scheme that may be used for this purpose when interactive disk-array based video servers are used. We assume presence of no buffer at the server and hence, all retrieved segments are immediately transmitted to the appropriate users. Such a retrieval scheme employs a macro-slot assigner and a disk scheduler. Macro-slots define a duration of time in a service round within which one video segment needs to be retrieved for a user. Having assigned macro-slots to users, the disk scheduler uses the non-preemptive earliest deadline first (N-EDF) algorithm to determine a valid schedule for segment retrieval. In order to increase the number of users that can be served by the system, the number of disk seeks in a service round needs to be decreased. This is done in the Scan-N-EDF algorithm by appropriately grouping retrievals and using the scan algorithm within each group. For a given video segment size, the amount of buffer required at each user's set-top box is reduced to two video segments. Guarantees are provided for the avoidance of video starvation as well as buffer overflow at each user's set-top box.