MORA: an Energy-Aware Slack Reclamation Scheme for Scheduling Sporadic Real-Time Tasks upon Multiprocessor Platforms

In this paper, we address the global and preemptive energy-aware scheduling problem of sporadic constrained-deadline tasks on DVFS-identical multiprocessor platforms. We propose an online slack reclamation scheme which profits from the discrepancy between the worst- and actual-case execution time of the tasks by slowing down the speed of the processors in order to save energy. Our algorithm called MORA takes into account the application-specific consumption profile of the tasks. We demonstrate that MORA does not jeopardize the system schedulability and we show by performing simulations that it can save up to 32% of energy (in average) compared to execution without using any energy-aware algorithm.Comment: 11 page

Power-Aware Real-Time Scheduling upon Identical Multiprocessor Platforms

In this paper, we address the power-aware scheduling of sporadic constrained-deadline hard real-time tasks using dynamic voltage scaling upon multiprocessor platforms. We propose two distinct algorithms. Our first algorithm is an off-line speed determination mechanism which provides an identical speed for each processor. That speed guarantees that all deadlines are met if the jobs are scheduled using EDF. The second algorithm is an on-line and adaptive speed adjustment mechanism which reduces the energy consumption while the system is running.Comment: The manuscript corresponds to the final version of SUTC 2008 conferenc

A Survey of Fault-Tolerance Techniques for Embedded Systems from the Perspective of Power, Energy, and Thermal Issues

The relentless technology scaling has provided a significant increase in processor performance, but on the other hand, it has led to adverse impacts on system reliability. In particular, technology scaling increases the processor susceptibility to radiation-induced transient faults. Moreover, technology scaling with the discontinuation of Dennard scaling increases the power densities, thereby temperatures, on the chip. High temperature, in turn, accelerates transistor aging mechanisms, which may ultimately lead to permanent faults on the chip. To assure a reliable system operation, despite these potential reliability concerns, fault-tolerance techniques have emerged. Specifically, fault-tolerance techniques employ some kind of redundancies to satisfy specific reliability requirements. However, the integration of fault-tolerance techniques into real-time embedded systems complicates preserving timing constraints. As a remedy, many task mapping/scheduling policies have been proposed to consider the integration of fault-tolerance techniques and enforce both timing and reliability guarantees for real-time embedded systems. More advanced techniques aim additionally at minimizing power and energy while at the same time satisfying timing and reliability constraints. Recently, some scheduling techniques have started to tackle a new challenge, which is the temperature increase induced by employing fault-tolerance techniques. These emerging techniques aim at satisfying temperature constraints besides timing and reliability constraints. This paper provides an in-depth survey of the emerging research efforts that exploit fault-tolerance techniques while considering timing, power/energy, and temperature from the real-time embedded systems’ design perspective. In particular, the task mapping/scheduling policies for fault-tolerance real-time embedded systems are reviewed and classified according to their considered goals and constraints. Moreover, the employed fault-tolerance techniques, application models, and hardware models are considered as additional dimensions of the presented classification. Lastly, this survey gives deep insights into the main achievements and shortcomings of the existing approaches and highlights the most promising ones

Experiences in Implementing an Energy-Driven Task Scheduler in RT-Linux

Dynamic voltage scaling (DVS) is being increasingly used for power management in embedded systems. Energy is a scarce resource in embedded real-time systems and energy consumption must be carefully balanced against realtime responsiveness. We describe our experiences in implementing an energy driven task scheduler in RT-Linux. We attempt to minimize the energy consumed by a taskset while guaranteeing that all task deadlines are met. Our algorithm, which we call LEDF, follows a greedy approach and schedules as many tasks as possible at a low CPU speed in a power-aware manner. We present simulation results on energy savings using LEDF, and we validate our approach using the RT-Linux testbed on the AMD Athlon 4 processor. Power measurements taken on the testbed closely match the power estimates obtained using simulation. Our results show that DVS results in significant energy savings for practical real-life task sets. We also show that when CPU speeds are restricted to only a few discrete values, this approach saves more energy than currently existing methods

Power-Aware Real-Time Scheduling on Identical Multiprocessor Platforms

In the following, we consider the problem of minimizing the energy consumption needed for executing a set of real-time tasks scheduled on a fixed number of identical processors. The scheduling is preemptive and follows the global EDF policy. ``Global'' scheduling algorithms, on the contrary to partitioned algorithms, allows different instances of the same task (also called jobs or processes) to be executed upon different processors. Each process can start its execution on any processor and may migrate at run-time from one processor to another if it gets preempted by smaller-deadline processes. We first tackle the problem of choosing the smallest admissible processor frequency for the set of CPUs such that all deadlines will be met considering the worst-case workload. The procedure is performed off-line and provides a static result in the sense that the computed speed does not change over time. Such a static solution is necessary, however, due to the discrepancy between worst-Case Execution Times (WCET) and Actual-Case Execution Times (ACET), it usually leads to very conservative results. In a second step, we thus propose an on-line ``slack reclaiming'' scheme that monitors task executions and take advantage of unused CPU time to further reduce frequency

A Dynamic Real-time Scheduling Algorithm for Reduced Energy Consumption

In embedded real-time systems, Dynamic Power Management (DPM) techniques have traditionally focused on reducing the dynamic power dissipation that occurs when a CMOS gate switches in a processor. Less attention has been given to processor leakage power or power consumed by I/O devices and other subsystems. I/O-based DPM techniques, however, have been extensively researched in non-real-time systems. These techniques focus on switching I/O devices to low power states based on various policies and are not applicable to real-time environments because of the non-deterministic nature of the policies. The challenge in conserving energy in embedded real-time systems is thus to reduce power consumption while preserving temporal correctness. To address this problem, we introduce three scheduling algorithms of increasing complexity: Energy-Aware EDF (EA-EDF), Enhanced Energy-Aware EDF (EEA-EDF) and Slack Utilization for Reduced Energy (SURE). The first two algorithms are relatively simple extensions to the Earliest Deadline First (EDF) scheduling algorithm that enable processor, I/O device, and subsystem energy conservation. The SURE algorithm utilizes slack to create a non-work-conserving approach to reducing power consumption. An evaluation of the three approaches shows that all three yield significant energy savings with respect to no DPM technique. The actual savings depends on the task set, shared devices, and the power requirements of the devices. When the cost of switching power states is low, the EA-EDF and EEA-EDF algorithms provide remarkable power savings considering their simplicity. In general, however, the higher the energy cost to switch power states, the more benefit SURE provides

Developing an energy efficient real-time system

Increasing number of battery operated devices creates a need for energy-efficient real-time operating system for such devices. Designing a truly energy-efficient system is a multi-staged effort; this thesis consists of three main tasks that address different aspects of energy efficiency of a real-time system (RTS). The first chapter introduces an energy-efficient algorithm that alternates processor frequency using DVFS to schedule tasks on cores. Speed profiles is calculated for every task that gives information about how long a task would run for and at what processor speed. We pair tasks with similar speed profiles to give us a resultant merged speed profile that can be efficient scheduled on a cluster. Experiments carried out on ODROID-XU3 are compared with a reference approach that provides energy saving of up to 20%. The second chapter proposes power-aware techniques to segregate a task set over a heterogeneous platform such that the overall energy consumption is minimized. With the help of calculated speed profiles, second contribution of this work feasibly partitions a given task set into individual sets for a cluster based homogeneous platform. Various heuristics are proposed that are compared against a baseline approach with simulation results. The final chapter of this thesis focuses on the importance of having an underlying energy-efficient operating system. We discuss an energy-efficient way of porting a real-time operating system (RTOS), QP, over TMS320F28377S along with modifications to make the Operating System (OS) consume minimal energy for its operation --Abstract, page iii

A Dynamic Real-time Scheduling Algorithm for Reduced Energy Consumption

In embedded real-time systems, Dynamic Power Management (DPM) techniques have traditionally focused on reducing the dynamic power dissipation that occurs when a CMOS gate switches in a processor. Less attention has been given to processor leakage power or power consumed by I/O devices and other subsystems. I/O-based DPM techniques, however, have been extensively researched in non-real-time systems. These techniques focus on switching I/O devices to low power states based on various policies and are not applicable to real-time environments because of the non-deterministic nature of the policies. The challenge in conserving energy in embedded real-time systems is thus to reduce power consumption while preserving temporal correctness. To address this problem, we introduce three scheduling algorithms of increasing complexity: Energy-Aware EDF (EA-EDF), Enhanced Energy-Aware EDF (EEA-EDF) and Slack Utilization for Reduced Energy (SURE). The first two algorithms are relatively simple extensions to the Earliest Deadline First (EDF) scheduling algorithm that enable processor, I/O device, and subsystem energy conservation. The SURE algorithm utilizes slack to create a non-work-conserving approach to reducing power consumption. An evaluation of the three approaches shows that all three yield significant energy savings with respect to no DPM technique. The actual savings depends on the task set, shared devices, and the power requirements of the devices. When the cost of switching power states is low, the EA-EDF and EEA-EDF algorithms provide remarkable power savings considering their simplicity. In general, however, the higher the energy cost to switch power states, the more benefit SURE provides

Partitioned EDF Scheduling in Multicore systems with Quality of Service constraints

International audienceIn this paper we study the partitioned EDF scheduling in a homogeneous multiprocessor environment with Quality of Service (QoS) constraints. The system considered here is a real-time multiprocessor system assumed to be powered by rechargeable batteries. We address the issue of how to best partition a set of firm real-time tasks that can occasionally skip one instance according to a predefined QoS threshold. The main goal is to minimize the energy consumption of the system while offering solutions with respect to transient energy starvation situations the system can experiment. The contribution of the paper is twofold. First, we present a schedulability analysis of firm multiprocessor task sets under QoS constraints. Second we propose new partitionning heuristics integrating skips. The evaluation is conducted from several points of view (minimization of the total processor number, maximization of the spare capacity on each processor)