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45
Network Flow Techniques for Dynamic Voltage Scaling in Hard RealTime Systems
 IEEE Transactions on ComputerAided Design of Integrated Circuits and Systems
, 2004
"... Energy consumption is an important performance parameter for portable and wireless embedded systems. However, energy consumption must be carefully balanced with realtime responsiveness in hard realtime systems. In this paper, we present two offline dynamic voltage scaling (DVS) schemes for dynamic ..."
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Energy consumption is an important performance parameter for portable and wireless embedded systems. However, energy consumption must be carefully balanced with realtime responsiveness in hard realtime systems. In this paper, we present two offline dynamic voltage scaling (DVS) schemes for dynamic power management in such systems. In the first method, we develop a generalized network flow (GNF) model for the uniprocessor DVS problem and solve it optimally using an efficient network flow algorithm. The proposed method outperforms existing DVS schemes for several popular embedded processors where the number of processor speeds is limited to a few values. The solutions for the GNF model provide theoretical lower bounds on energy consumption using DVS in hard realtime systems. We also describe a minimumcost network flow model whose solutions are nearoptimal. The minimumcost models perform at par with competing methods for processor models with a large range of operating voltages, and better than them for processor models with a limited set of operating voltages.
EnergyAware Task Scheduling With Task Synchronization for Embedded RealTime Systems
, 2006
"... Slowdown factors determine the extent of slowdown that a computing system can experience based on functional and performance requirements. Dynamic voltage scaling (DVS) of a processor based on slowdown factors can lead to considerable energy savings. This paper addresses the problem of DVS in the p ..."
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Slowdown factors determine the extent of slowdown that a computing system can experience based on functional and performance requirements. Dynamic voltage scaling (DVS) of a processor based on slowdown factors can lead to considerable energy savings. This paper addresses the problem of DVS in the presence of task synchronization. Tasks synchronize to enforce mutually exclusive access to the shared resources and can be blocked by lower priority tasks. Task slowdown factors that guarantee meeting all task deadlines are computed. Both static and dynamic priority scheduling viz. rate monotonic (RM) scheduling and earliest deadline first (EDF) scheduling, respectively, are studied.
ParaScale: Exploiting Parametric Timing Analysis for RealTime Schedulers and Dynamic Voltage Scaling
 Proceedings of the IEEE RealTime Systems Symposium
, 2005
"... Static timing analysis safely bounds worstcase execution times to determine if tasks can meet their deadlines in hard realtime systems. However, conventional timing analysis requires that the upper bound of loops be known statically, which limits its applicability. Parametric timing analysis metho ..."
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Static timing analysis safely bounds worstcase execution times to determine if tasks can meet their deadlines in hard realtime systems. However, conventional timing analysis requires that the upper bound of loops be known statically, which limits its applicability. Parametric timing analysis methods remove this constraint by providing the WCET as a formula parameterized on loop bounds. This paper contributes a novel technique to allow parametric timing analysis to interact with dynamic realtime schedulers. By dynamically detecting actual loop bounds, a lower WCET bound can be calculated, onthefly, for the remaining execution of a task. We analyze the benefits from parametric analysis in terms of dynamically discovered slack in a schedule. We then assess the potential for dynamic power conservation by exploiting parametric loop bounds for ParaScale, our intratask dynamic voltage scaling (DVS) approach. Our results demonstrate that the parametric approach to timing analysis provides 66%80% additional savings in power consumption. We further show that using this approach combined with online intratask DVS to exploit parametric execution times results in much lower power consumption. Hence, even in the absence of dynamic scheduling, significant savings in power can be obtained, e.g., in the case of cyclic executives. 1.
BlockingAware Processor Voltage Scheduling for RealTime Tasks
 ACM Transactions on Embedded Computing Systems
, 2003
"... this paper, we study voltage scheduling for realtime periodic tasks with nonpreemptible sections. Three schemes are proposed: The static speed algorithm derives the minimum static feasible speed based on the Stack Resource Policy (SRP). Due to blocking, this static speed is usually higher than the ..."
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this paper, we study voltage scheduling for realtime periodic tasks with nonpreemptible sections. Three schemes are proposed: The static speed algorithm derives the minimum static feasible speed based on the Stack Resource Policy (SRP). Due to blocking, this static speed is usually higher than the speed required for scheduling fully preemptible tasks (called the utilization speed). Two dynamic speed algorithms are then introduced to further reduce energy consumption. The novel dual speed algorithm operates the processor at the utilization speed whenever possible and switches to the higher static speed only when blocking occurs. The dual speed dynamic reclaiming (DSDR) algorithm reserves time budget for each job, reclaims the unused time budget from completed jobs and redistributes it to subsequent jobs so they can run at a lower speed whenever possible. Feasibility conditions for realtime task sets have been derived and proved mathematically. Simulation results show that the proposed voltage scheduling algorithms dramatically reduce processor energy consumption over nonpoweraware scheduling algorithms. Furthermore, the two dynamic speed algorithms consistently outperform the static speed scheme in a wide range of system and workload conditions
Energy Aware Nonpreemptive Scheduling for Hard RealTime Systems
 ECRTS
, 2005
"... Slowdown based on dynamic voltage scaling (DVS) provides the ability to perform an energydelay tradeoff in the system. Nonpreemptive scheduling becomes an integral part of systems where resource characteristics makes preemption undesirable or impossible. We address the problem of energy efficient ..."
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Slowdown based on dynamic voltage scaling (DVS) provides the ability to perform an energydelay tradeoff in the system. Nonpreemptive scheduling becomes an integral part of systems where resource characteristics makes preemption undesirable or impossible. We address the problem of energy efficient scheduling of nonpreemptive tasks based on the Earliest Deadline First (EDF) scheduling policy. We present the stack based slowdown algorithm that builds upon the optimal feasibility test for nonpreemptive systems. We also propose a dynamic slack reclamation policy to further enhance energy savings. Simulation results show on an average 15 % energy savings using static slowdown factors and 20 % savings with dynamic slowdown, over known slowdown techniques. 1
A Linear Algorithm For RealTime Scheduling With Optimal Energy Use
, 2003
"... We present an algorithm for scheduling a set of nonrecurrent tasks (or jobs) with FIFO realtime constraints so as to minimize the total energy consumption on a dynamically variable voltage processor. Our algorithm runs in linear time and is thus an improvement over the classical algorithm of Yao e ..."
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We present an algorithm for scheduling a set of nonrecurrent tasks (or jobs) with FIFO realtime constraints so as to minimize the total energy consumption on a dynamically variable voltage processor. Our algorithm runs in linear time and is thus an improvement over the classical algorithm of Yao et al. [14] in this case. It was made possible by considering the problem as a shortest path problem. We also propose an algorithm for the case where the processor possesses only a limited number of clock frequencies. We extend this algorithm to provide the minimum number of speed changes, which is important when the speed switching overhead cannot be neglected. All our algorithms are linear in the number of tasks if the arrivals and deadlines are sorted and need O(N log N) time otherwise and these complexities are shown optimal. We extend the results to uid tasks and nonconvex cost functions.
Parametric Timing Analysis and Its Application to Dynamic Voltage Scaling
, 2010
"... Embedded systems with realtime constraints depend on a priori knowledge of worstcase execution times (WCETs) to determine if tasks meet deadlines. Static timing analysis derives bounds on WCETs but requires statically known loop bounds. This work removes the constraint on known loop bounds through ..."
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Embedded systems with realtime constraints depend on a priori knowledge of worstcase execution times (WCETs) to determine if tasks meet deadlines. Static timing analysis derives bounds on WCETs but requires statically known loop bounds. This work removes the constraint on known loop bounds through parametric analysis expressing WCETs as functions. Tighter WCETs are dynamically discovered to exploit slack by dynamic voltage scaling (DVS) saving 60 % to 82 % energy over DVSoblivious techniques and showing savings close to more costly dynamicpriority DVS algorithms. Overall, parametric analysis expands the class of realtime applications to programs with loopinvariant dynamic loop bounds while retaining tight WCET bounds.
PowerAware RealTime Scheduling upon Identical Multiprocessor Platforms
 IEEE INTERNATIONAL CONFERENCE ON SENSOR NETWORKS, UBIQUITOUS, AND TRUSTWORTHY COMPUTING
, 2008
"... In this paper, we address the poweraware scheduling of sporadic constraineddeadline hard realtime tasks using dynamic voltage scaling upon multiprocessor platforms. We propose two distinct algorithms. Our first algorithm is an offline speed determination mechanism which provides an identical spe ..."
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In this paper, we address the poweraware scheduling of sporadic constraineddeadline hard realtime tasks using dynamic voltage scaling upon multiprocessor platforms. We propose two distinct algorithms. Our first algorithm is an offline 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 online and adaptive speed adjustment mechanism which reduces the energy consumption while the system is running.
MORA: an EnergyAware Slack Reclamation Scheme for Scheduling Sporadic RealTime Tasks upon Multiprocessor Platforms
, 906
"... In this paper, we address the global and preemptive energyaware scheduling problem of sporadic constraineddeadline tasks on DVFSidentical multiprocessor platforms. We propose an online slack reclamation scheme which profits from the discrepancy between the worst and actualcase execution time of ..."
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In this paper, we address the global and preemptive energyaware scheduling problem of sporadic constraineddeadline tasks on DVFSidentical multiprocessor platforms. We propose an online slack reclamation scheme which profits from the discrepancy between the worst and actualcase 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 applicationspecific 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 energyaware algorithm. 1.
A Dual Speed Approach to WorkloadAware Voltage Scaling
"... Dynamic voltage scaling (DVS) is a frequently used technique in mobile and embedded systems, aimed at reducing the energy consumption of mobile processors. A key challenge with DVS is to maximize the energy savings while ensuring that applications ’ realtime requirements are met. This paper experi ..."
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Dynamic voltage scaling (DVS) is a frequently used technique in mobile and embedded systems, aimed at reducing the energy consumption of mobile processors. A key challenge with DVS is to maximize the energy savings while ensuring that applications ’ realtime requirements are met. This paper experimentally evaluates the DVS capabilities of a mobile platform based on the XScale PXA255 processor and introduces a novel DVS approach, called Loadaware Dualspeed Dynamic Voltage Scaling (LDDVS), that increases the obtainable energy savings. In systems with a discrete number of frequency levels, existing dualspeed DVS approaches compute an optimal theoretical CPU speed and approximate it by choosing the two neighboring discrete speed levels. This work compares experimentally the energy savings attained with different frequency combinations and shows that choosing the two neighboring frequency levels does not necessarily yield the highest energy savings. As a result of the above observation, this work introduces an online approach to dualspeed DVS that formulates a model for speed selection based on the workload characteristics 1 of the current task set and computes a frequency pair that yields the best possible energy savings for a given taskset and workload. 1