On the periodic behavior of real-time schedulers on identical multiprocessor platforms

This paper is proposing a general periodicity result concerning any deterministic and memoryless scheduling algorithm (including non-work-conserving algorithms), for any context, on identical multiprocessor platforms. By context we mean the hardware architecture (uniprocessor, multicore), as well as task constraints like critical sections, precedence constraints, self-suspension, etc. Since the result is based only on the releases and deadlines, it is independent from any other parameter. Note that we do not claim that the given interval is minimal, but it is an upper bound for any cycle of any feasible schedule provided by any deterministic and memoryless scheduler

Restart-Based Fault-Tolerance: System Design and Schedulability Analysis

Embedded systems in safety-critical environments are continuously required to deliver more performance and functionality, while expected to provide verified safety guarantees. Nonetheless, platform-wide software verification (required for safety) is often expensive. Therefore, design methods that enable utilization of components such as real-time operating systems (RTOS), without requiring their correctness to guarantee safety, is necessary. In this paper, we propose a design approach to deploy safe-by-design embedded systems. To attain this goal, we rely on a small core of verified software to handle faults in applications and RTOS and recover from them while ensuring that timing constraints of safety-critical tasks are always satisfied. Faults are detected by monitoring the application timing and fault-recovery is achieved via full platform restart and software reload, enabled by the short restart time of embedded systems. Schedulability analysis is used to ensure that the timing constraints of critical plant control tasks are always satisfied in spite of faults and consequent restarts. We derive schedulability results for four restart-tolerant task models. We use a simulator to evaluate and compare the performance of the considered scheduling models

Schedulability of Rate Monotonic Algorithm using Improved Time Demand Analysis for Multiprocessor Environment

Real-Time Monotonic algorithm (RMA) is a widely used static priority scheduling algorithm. For application of RMA at various systems, it is essential to determine the system’s feasibility first. The various existing algorithms perform the analysis by reducing the scheduling points in a given task set. In this paper we propose a schedubility test algorithm, which reduces the number of tasks to be analyzed instead of reducing the scheduling points of a given task. This significantly reduces the number of iterations taken to compute feasibility. This algorithm can be used along with the existing algorithms to effectively reduce the high complexities encountered in processing large task sets. We also extend our algorithm to multiprocessor environment and compare number of iterations with different number of processors. This paper then compares the proposed algorithm with existing algorithm. The expected results show that the proposed algorithm performs better than the existing algorithms

Review of different approaches for optimal performance of multi-processors

We reviewed the literature used for optimal performance of multi-processor, we study different approaches in this paper. They include rate monotonic, deadline monotonic, and Earliest deadline first Algorithm. These approaches are basically used for real time scheduling systems .The problem of inconsistencies occurring in these algorithms such as those tasks whose task period is less but if not executed does not matter and whenever they are scheduled under rate monotonic scheduling algorithm the time consumed by CPU in scheduling the tasks is spent unnecessarily

Scheduling Techniques for Operating Systems for Medical and IoT Devices: A Review

Software and Hardware synthesis are the major subtasks in the implementation of hardware/software systems. Increasing trend is to build SoCs/NoC/Embedded System for Implantable Medical Devices (IMD) and Internet of Things (IoT) devices, which includes multiple Microprocessors and Signal Processors, allowing designing complex hardware and software systems, yet flexible with respect to the delivered performance and executed application. An important technique, which affect the macroscopic system implementation characteristics is the scheduling of hardware operations, program instructions and software processes. This paper presents a survey of the various scheduling strategies in process scheduling. Process Scheduling has to take into account the real-time constraints. Processes are characterized by their timing constraints, periodicity, precedence and data dependency, pre-emptivity, priority etc. The affect of these characteristics on scheduling decisions has been described in this paper

Time Triggered Scheduling Analysis for Real-Time Applications on Multicore Platforms

REACTION 2014. 3rd International Workshop on Real-time and Distributed Computing in Emerging Applications. Rome, Italy. December 2nd, 2014.Scheduling of real-time applications for multicore platforms has become an important research topic. For analyzing the timing satisfactions of real-time tasks, most researches in the literature assume independent tasks. However, industrial applications are usually with fully tangled dependencies among the tasks. Independence of the tasks provides a very nice abstraction, whereas dependent structures due to the tangled executions of the tasks are closer to the real systems. This paper studies the scheduling policies and the schedulabil-ity analysis based on independent tasks by hiding the execution dependencies with additional timing parameters. Our scheduling policy relates to the well-known periodic task model, but in contrast, tasks are able to communicate with each other. A feasible task set requires an analysis for each core and the communication infrastructure, which can be performed indi-vidually by decoupling computation from communication in a distributed system. By using a Time-Triggered Constant Phase (TTCP) scheduler, each task receives certain time-slots in the hyper-period of the task set, which ensures a time-predictable communication impact. In this paper, we provide several algorithms to derive the time-slot for each task. Further, we found a fast heuristic algorithm to calculate the time-slot for each task, which is capable to reach a core utilization of 90% by considering typical industrial applications. Finally, experiments show the effectiveness of our heuristic and the performance in different settings.Publicad

Schedulability, Response Time Analysis and New Models of P-FRP Systems

Functional Reactive Programming (FRP) is a declarative approach for modeling and building reactive systems. FRP has been shown to be an expressive formalism for building applications of computer graphics, computer vision, robotics, etc. Priority-based FRP (P-FRP) is a formalism that allows preemption of executing programs and guarantees real-time response. Since functional programs cannot maintain state and mutable data, changes made by programs that are preempted have to be rolled back. Hence in P-FRP, a higher priority task can preempt the execution of a lower priority task, but the preempted lower priority task will have to restart after the higher priority task has completed execution. This execution paradigm is called Abort-and-Restart (AR). Current real-time research is focused on preemptive of non-preemptive models of execution and several state-of-the-art methods have been developed to analyze the real-time guarantees of these models. Unfortunately, due to its transactional nature where preempted tasks are aborted and have to restart, the execution semantics of P-FRP does not fit into the standard definitions of preemptive or non-preemptive execution, and the research on the standard preemptive and non-preemptive may not applicable for the P-FRP AR model. Out of many research areas that P-FRP may demands, we focus on task scheduling which includes task and system modeling, priority assignment, schedulability analysis, response time analysis, improved P-FRP AR models, algorithms and corresponding software. In this work, we review existing results on P-FRP task scheduling and then present our research contributions: (1) a tighter feasibility test interval regarding the task release offsets as well as a linked list based algorithm and implementation for scheduling simulation; (2) P-FRP with software transactional memory-lazy conflict detection (STM-LCD); (3) a non-work-conserving scheduling model called Deferred Start; (4) a multi-mode P-FRP task model; (5) SimSo-PFRP, the P-FRP extension of SimSo - a SimPy-based, highly extensible and user friendly task generator and task scheduling simulator.Computer Science, Department o

Accelerated Simply Periodic Task Sets for RM Scheduling

International audienceThe article examines rate-monotonic scheduling (RMS). The focus is on efficient schedulability tests of high sensitivity.Accelerated simply periodic task sets (ASPTSs) are constructed by shortening task periods in order to obtain a transformed – simply periodic – task set where each period is an integer divisor of all longer periods. The article presents a new heuristic for partitioned multiprocessor (MP) scheduling based on Specialization with respect to r (Sr) and Distance-Constrained Tasks (DCT) which use ASPTSs first described by Han and Tyan [9, 10]. They have al- ready shown the advantage of Sr and DCT over the Liu/Layland (LL) and the Burchard (Bu) bound in terms of sensitivity. First, the article compares Sr and DCT as well with other uniprocessor scheduling criteria, both theoretically and empirically. Next, these tests are applied to MP scheduling. Theory is followed by a case study and an empirical investigation with randomised task sets. Related approaches are thoroughly examined and summarised in a scheme where the central role of ASPTSs becomes obvious.The article shows that Sr and DCT provide a very good trade-off between maximizing the scheduling test sensitivity (no unnecessary hardware) and minimizing the test’s computational complexity (towards real-time decisions on schedulability)

Analysis of Real-Time Capabilities of Dynamic Scheduled System

This PhD-thesis explores different real-time scheduling approaches to effectively utilize industrial real-time applications on multicore or manycore platforms. The proposed scheduling policy is named the Time-Triggered Constant Phase scheduler for handling periodic tasks, which determines time windows for each computation and communication in advance by using the dependent task model