Rate Monotonic Research Articles

Energy-efficient scheduling of real-time tasks with shared resources

This paper explores the energy-efficient scheduling of real-time tasks on a non-ideal DVS processor in the presence of resource sharing. We assume that tasks are periodic, preemptive and may access to shared resources. When dynamic-priority and fixed-priority scheduling are considered, we use the earliest deadline first (EDF) algorithm and the rate monotonic (RM) algorithm to schedule the given set of tasks. Based on the stack resource policy (SRP), we propose an approach, called blocking-aware two-speed (BATS) algorithm, to synchronize the tasks with shared resources and to calculate appropriate execution speeds so that the shared resources can be accessed in a mutual exclusive manner and the energy consumption can be reduced. Particularly, BATS uses a static low speed to execute tasks initially, and then it switches to a high speed dynamically whenever a task blocks a higher priority task. More specifically, the processor runs at the high speed from the beginning of the blocking until the deadline of the blocked task or the processor becomes idle. In order to guarantee that the deadlines of tasks are met, the static low speed and the dynamic high speeds are derived based on the theoretical analysis of the schedulability of tasks. Compared with existing work, BATS achieves more energy saving because its dynamic high speeds are lower than that of existing work and the processor has less chance to execute tasks at the high speeds. The schedulability analysis and the properties of our proposed BATS are provided in this paper. We also evaluated the capabilities of BATS by a series of experiments, for which we have some encouraging results.

Energy Efficient Real-Time Task Scheduling for Embedded Systems with Hybrid Main Memory

Available energy becomes a critical design issue for the increasingly complex real-time embedded systems. Phase Change Memory (PCM), with high density and low idle power, has recently been extensively studied as a promising alternative of DRAM. Hybrid PCM-DRAM main memory architecture has been proposed to leverage the low power of PCM and high speed of DRAM. In this paper, we propose energy-aware real-time task scheduling strategies for hybrid PCM-DRAM based embedded systems. Given the execution time variation when a task is loaded into PCM or DRAM, we re-design the static table-driven scheduling for a set of fixed tasks, as well as the Rate-Monotonic (RM) and Earliest Deadline First (EDF) scheduling policies for periodic task sets. Furthermore, since the actual execution time can be much shorter than the worst-case execution time in the actual execution, we propose online schedulers which migrates the tasks between PCM and DRAM to optimize the energy consumption by utilizing the slack time resulted from the completed tasks. All the proposed algorithms minimize the number of task migrations from PCM to DRAM by ensuring that aperiodic tasks are not migrated while each periodic task instance can be migrated at most once. Experimental results show our proposed scheduling algorithms satisfy the real-time constraints and significantly reduce the energy consumption.

A Review of Sufficient Schedulability Analysis for Fixed Priority Scheduling Systems

This papercarries out a survey of sufficient schedulability analysis forfixed priority (FP) scheduling. The most common used fixed priority assignment is the rate monotonic (RM) algorithm, according to its policy, the task priorities are ordered based on their activation rates, so that the task with the shortest period is assigned the highest priority. However, when each task’s relative deadline is not equal to its period, the RM algorithm is not suitable to assign the task priorities. When relative deadlines are less than or equal to periods,the deadline monotonic (DM) algorithm can be deployed to schedule the tasks. The utilization based schedulability analysis has the advantage of simple implementation, and manyexisting schedulability analyses on uniprocessor are covered.

Improvement of adaptive EDF

Rate monotonic (RM) and earliest deadline first (EDF) are representative scheduling algorithms for real-time periodic tasks. RM has a merit that tasks with high-priority (short-period) have small jitters and short response times. However, it is impossible that processor utilization reaches 100% while maintaining schedulability or that tasks are given importance independent of their periods. On the other hand, EDF can utilize processors by 100% while it cannot give tasks fixed priorities or importance. Therefore, it is difficult to keep jitters or response times of particular tasks short. The author proposed an EDF-based method, Adaptive EDF, of shortening response times of a task that is important for the system by introducing predictive execution times (PET) and dividing execution of the task into two sub instances based on PET [1]. This paper shows improved techniques which can further reduce response times by extending the adaptive EDF.

Enhanced utilization bound of Rate-Monotonic scheduling in Controller Area Networks

When priorities to message streams are assigned using Rate Monotonic (RM) for a Controller Area Network (CAN), the utilization bound is known to be about 25% for CAN 2.0A and 29% for CAN 2.0B. In this letter, we present a higher utilization bound than the existing ones with a reasonable constraint. The new utilization bounds are approximately 34% for CAN 2.0A and 41% for CAN 2.0B if no single message stream's utilization exceeds 46% or 27% of the total utilization for CAN 2.0A or CAN 2.0B, respectively.

Analysis and Optimization of Rail Vehicles Networked Control System Based on Static Scheduling Algorithm

The system performance of rail vehicles NCS mainly depends on communication performance and control performance. Because of considerably limited availability of computing resources, real-time scheduling of shared resources is among the factors that greatly impact system performance. From a real-time control perspective, the problem of real-time scheduling in NCS is illustrated based on timing analysis of a typical NCS. Take the MVB of rail vehicle NCS for example, The theory and practice of synchronously static Rate Monotonic(RM)are introduced into rail vehicle NCS, with special focus on open-up scheduling and adaptive scheduling, which made communication simplified and reliable. At the same time, build objective function of system performance based on state space equation, wholly benefits optimized design of rail vehicle NCS, considering both communication performance and control performance.

SS-DRM: Semi-Partitioned Scheduling Based on Delayed Rate Monotonic on Multiprocessor Platforms

Semi-partitioned scheduling is a new approach for allocating tasks on multiprocessor platforms. By splitting some tasks between processors, semi-partitioned scheduling is used to improve processor utilization. In this paper, a new semi-partitioned scheduling algorithm called SS-DRM is proposed for multiprocessor platforms. The scheduling policy used in SS-DRM is based on the delayed rate monotonic algorithm, which is a modified version of the rate monotonic algorithm that can achieve higher processor utilization. This algorithm can safely schedule any system composed of two tasks with total utilization less than or equal to that on a single processor. First, it is formally proven that any task which is feasible under the rate monotonic algorithm will be feasible under the delayed rate monotonic algorithm as well. Then, the existing allocation method is extended to the delayed rate monotonic algorithm. After that, two improvements are proposed to achieve more processor utilization with the SS-DRM algorithm than with the rate monotonic algorithm. According to the simulation results, SS-DRM improves the scheduling performance compared with previous work in terms of processor utilization, the number of required processors, and the number of created subtasks.

Ec-A: A Task Allocation Algorithm for Energy Minimization in Multiprocessor Systems

With the necessity of increased processing capacity with less energy consumption; power aware multiprocessor system has gained more attention in the recent future. One of the additional challenges that is to be solved in a multi-processor system when compared to uni-processor system is job allocation. This paper presents a novel task dependent job allocation algorithm: Energy centric- Allocation (Ec-A) and Rate Monotonic (RM) scheduling to minimize energy consumption in a multiprocessor system. A simulation analysis is carried out to verify the performance increase with reduction in energy consumption and required number of processors in the system.

Power-aware fixed priority scheduling for sporadic tasks in hard real-time systems

In this paper, we consider the generalized power model in which the focus is the dynamic power and the static power, and we study the problem of the canonical sporadic task scheduling based on the rate-monotonic (RM) scheme. Moreover, we combine with the dynamic voltage scaling (DVS) and dynamic power management (DPM). We present a static low power sporadic tasks scheduling algorithm (SSTLPSA), assuming that each task presents its worst-case work-load to the processor at every instance. In addition, a more energy efficient approach called a dynamic low power sporadic tasks scheduling algorithm (DSTLPSA) is proposed, based on reclaiming the dynamic slack and adjusting the speed of other tasks on-the-fly in order to reduce energy consumption while still meeting the deadlines. The experimental results show that the SSTLPSA algorithm consumes 26.55–38.67% less energy than that of the RM algorithm and the DSTLPSA algorithm reduces the energy consumption up to 18.38–30.51% over the existing DVS algorithm.

Performance Evaluation of New Joint EDF-RM Scheduling Algorithm for Real Time Distributed System

In Real Time System, the achievement of deadline is the main target of every scheduling algorithm. Earliest Deadline First (EDF), Rate Monotonic (RM), and least Laxity First are some renowned algorithms that work well in their own context. As we know, there is a very common problem Domino's effect in EDF that is generated due to overloading condition (EDF is not working well in overloading situation). Similarly, performance of RM is degraded in underloading condition. We can say that both algorithms are complements of each other. Deadline missing in both events happens because of their utilization bounding strategy. Therefore, in this paper we are proposing a new scheduling algorithm that carries through the drawback of both existing algorithms. Joint EDF-RM scheduling algorithm is implemented in global scheduler that permits task migration mechanism in between processors in the system. In order to check the improved behavior of proposed algorithm we perform simulation. Results are achieved and evaluated in terms of Success Ratio (SR), Average CPU Utilization (ECU), Failure Ratio (FR), and Maximum Tardiness parameters. In the end, the results are compared with the existing (EDF, RM, and D_R_EDF) algorithms. It has been shown that the proposed algorithm performs better during overloading condition as well in underloading condition.

An SRP-based energy-efficient scheduling algorithm for dependent real-time tasks

In this paper, we are interested in the energy-efficient scheduling of dependent real-time tasks which may access multiunit resources. Based on the well-known stack resource policy (SRP), we propose the blocking-time stealing (BTS) algorithm to schedule dynamic-priority and fixed-priority tasks on a non-ideal dynamic voltage scaling (DVS) processor. Under the BTS algorithm, tasks are scheduled to be executed at proper processor speeds which are determined according to the sufficient schedulability conditions of the earliest deadline first (EDF) and the rate monotonic (RM) algorithms. The BTS algorithm measures dynamically the slack between the actual blocking time of a task and its estimated worst-case blocking time. The slack is then exploited to lower the processor speed guaranteeing that the feasibility of tasks is not affected. As a result, the energy consumption can be reduced while satisfying the timing constraints of real-time tasks.

Utilization Bound Scheduling Analysis for Nonpreemptive Uniprocessor Architecture Using UML-RT

The key for adopting the utilization-based schedulability test is to derive the utilization bound. Given the computation times, this paper proposes two utilization bound algorithms to derive interrelease times for nonpreemptive periodic tasks, using a new priority scheme, “Rate Monotonic Algorithm-Shortest Job First.” The obtained task set possesses the advantage of Rate Monotonic Algorithm and Shortest Job First priority scheme. Further, the task set is tested for schedulability, by first deriving a general schedulability condition from “problem window” analysis and, a necessary and sufficient schedulability condition for a task to be scheduled, at any release time are also derived. As a technical contribution, success ratio and effective processor utilization are analyzed for our proposed utilization bound algorithms on a uniprocessor architecture modeled using UML-RT.

Adaptive EDF

Along with the growing diversity and complexity of real-time embedded systems, significance of real-time scheduling is increasing. Rate monotonic (RM) and earliest deadline first (EDF) are representative scheduling algorithms for periodic tasks. RM has a merit that tasks with high-priority (short-period) have small jitters and short response times. However, it is impossible that processor utilization reaches 100% while maintaining schedulability or that tasks are given importance independent of their periods. On the other hand, EDF can utilize processors by 100% with schedulability, while it cannot give tasks fixed priorities or importance, therefore, it is difficult to keep jitters or response times of particular tasks short. This paper, in EDF algorithm, proposes a method of shortening response times of a task that is important for the system by introducing predictive execution times and dividing execution of the important task into two instances based on the predictive execution times. The use of predictive execution times has an effect of making deadline of the first instance earlier and therefore the first instance would be executed earlier by EDF. In the evaluation by simulation, the proposed method reduced average response times of the most important task by up to 14.2%.

Efficient schedulability tests for real-time embedded systems with urgent routines

Task scheduling is one of the key mechanisms to ensure timeliness in embedded real-time systems. Such systems have often the need to execute not only application tasks but also some urgent routines (e.g. error-detection actions, consistency checkers, interrupt handlers) with minimum latency. Although fixed-priority schedulers such as Rate-Monotonic (RM) are in line with this need, they usually make a low processor utilization available to the system. Moreover, this availability usually decreases with the number of considered tasks. If dynamic-priority schedulers such as Earliest Deadline First (EDF) are applied instead, high system utilization can be guaranteed but the minimum latency for executing urgent routines may not be ensured.In this paper we describe a scheduling model according to which urgent routines are executed at the highest priority level and all other system tasks are scheduled by EDF. We show that the guaranteed processor utilization for the assumed scheduling model is at least as high as the one provided by RM for two tasks, namely \(2(\sqrt{2}-1)\). Seven polynomial time tests for checking the system timeliness are derived and proved correct. The proposed tests are compared against each other and to an exact but exponential running time test.

A Priority-Based CSMA/CA Mechanism to Support Deadline-Aware Scheduling in Home Automation Applications Using IEEE 802.15.4

The wireless sensor networks (WSNs) are characterized by several small nodes able to perform measurements on one or more parameters and to communicate with each other through several protocols. Most of home automation networks (depending on the specific application) are mainly characterized by periodic traffic flows. In soft real-time contexts, the main problem is represented by the efficient allocation of guaranteed time slots (GTSs) for periodic traffic flows transmission in IEEE 802.15.4 networks. Moreover, it is important to ensure adequate performance for those embedded devices competing for the access to the medium through the carrier sense multiple access/collision avoidance algorithm (CSMA/CA). The main aim of this paper is to show a new approach for network flows scheduling in home automation applications based on IEEE 802.15.4 wireless sensor networks. This work addresses several advantages due to the introduction of rate monotonic (RM) for guaranteed time slots (GTSs) allocation combined with priority-based CSMA/CA for latencies reduction on transmission attempts as clearly demonstrated by obtained results.

Real-Time Industrial Automation Process Control using Network-Enabled RFID

The emerging ubiquitous computing technology that belongs to the group of automatic identification technologies and has become popular is the Radio Frequency Identification System involving electromagnetic theory for identifying human beings, animals, and most importantly useful in various fields like drug discovery, tracking and distribution of various materials, and data warehouse management. In recent times, it is found that the ubiquitous technology has been extended to numerous industrial applications involving real-time decisions. This system termed as “networks of RFID systems” helps in controlling various parameters and systems in realtime environment. Scheduling of real-time systems is important since it helps in satisfying the timing constraints where tasks in real-time systems are decided on the basis of deadline, occurrence period and slack time. Few algorithms based on these criteria are Rate Monotonic (RM), Earliest Deadline First (EDF), and Least-Laxity-First (LLF) algorithms. EDF and LLF are considered to be dynamic in nature while RM is static in nature. To judge the efficiency of the algorithms two conditions like “overloaded” and “under loaded” are taken into consideration. In this article, an effort is made to combine the features of both static as well as dynamic algorithms. in order to control the real-time industrial processes. Hence the major issue of concern in this paper is to resolve two issues, onedetermine the algorithm in terms of timing performance of different sub-processes so as to properly schedule them and other, how the timing constraints determine the behavior of the system need to be specified and thereby, to ensure that the algorithms meet the constraints under both overloaded and under loaded conditions.

A Work-Demand Analysis Compatible with Preemption-Aware Scheduling for Power-Aware Real-Time Tasks

Due to the importance of slack time utilization for power-aware scheduling algorithms,we propose a work-demand analysis method called parareclamation algorithm (PRA) to increase slack time utilization of the existing real-time DVS algorithms. PRA is an online scheduling for power-aware real-time tasks under rate-monotonic (RM) policy. It can be implemented and fully compatible with preemption-aware or transition-aware scheduling algorithms without increasing their computational complexities. The key technique of the heuristics method doubles the analytical interval and turns the deferrable workload out the potential slack time. Theoretical proofs show that PRA guarantees the task deadlines in a feasible RM schedule and takes linear time and space complexities. Experimental results indicate that the proposed method combining the preemption-aware methods seamlessly reduces the energy consumption by 14% on average over their original algorithms.

Design of New Dual-Motor Independent Drive System for Electric Vehicle

Multi-motor wheel independent driving technology is an important direction of electric vehicle(EV). Based on the analysis of the features of existing independent driving system of electric vehicle, a new dual-motor independent driving system configuration was designed. Complete parameters matching and simulation analysis of the system include motor, reducer, and battery. Distributed control network architecture based on high-speed CAN bus was developed, and information scheduling was optimized and real-time predictability was analyzed based on the rate monotonic (RM) algorithm and jitter margin index. The vehicle lateral stability control was achieved based on coordinated electro-hydraulic active braking. Based on the new dual-motor independent driving system, a new battery electric car was designed and tested. The results show that the vehicle has excellent dynamic and economic performance.

Minimal Task Allocation in Multiprocessors using improved next-fit for RM scheduling

processor allocation in multiprocessors can be accomplished efficiently for reducing the required number of processors for the given task set, accounting reduced power consumption with maximum processor utilization. This work is based on next fit algorithm using Rate Monotonic Algorithm (RMA) for a fixed priority system. The work proposes a minimal task allocation algorithm for multiprocessor environment. The proposed method reduces the number of processors required for a given task set using improved next fit algorithm and the same has been evaluated and tested. The proposed algorithm gives better results when there is large number of tasks in the system.

An experimental comparison of different real-time schedulers on multicore systems

In this work, an experimental comparison among the Rate Monotonic (RM) and Earliest Deadline First (EDF) multiprocessor real-time schedulers is performed, with a focus on soft real-time systems. We generated random workloads of synthetic periodic task sets and executed them on a big multi-core machine, using Linux as Operating System, gathering an extensive amount of data related to their exhibited performance under various real-time scheduling strategies. The comparison involves the fixed-priority scheduler for multiprocessors as available in the Linux kernel (with priorities set so as to achieve RM), and on our own implementation of EDF, both configured in global, partitioned and clustered mode. The impact of the various scheduling strategies on the performance of the applications, as well as the generated scheduling overheads, are compared presenting an extensive set of experimental results. These provide a comprehensive view of the performance achievable by the different schedulers under various workload conditions.