Abstract
Dynamic Voltage Scaling (DVS) is a promising method to achieve energy saving by slowing down the processor into multiple frequency levels in battery-operated embedded systems. However, the worst case execution time (WCET) of the tasks scheduled by DVS must be known ahead of time to ensure their schedulability. In reality, a system’s workloads may change significantly without satisfying any prediction. In other words, a task’s WCET may not provide useful information about its future real execution time (RET). This paper presents a novel Dynamic-Mode EDF scheduling algorithm when workloads change significantly. One of the Single-Mode, Dual-Mode, and Three-Mode frequency setting formats can be applied, based on the RET and the accumulated slack at run-time. Only one combination of the number of modes/speeds, speed-switching transition points, and the frequency scaling factor for each mode can lead to the best energy saving. Experimental results show that, given an RET pattern, our Dynamic-Mode DVS algorithm achieves an average 15% energy savings over the traditional two-mode DVS scheme on hard real-time systems. Additionally, we also consider speed-switching or energy transition overhead, and implement a preliminary test of our proposed algorithm. With a less aggressive voltage scaling strategy (fewer speed changes for each job), deadlines can still be strictly satisfied and an average of 14% energy consumption saving over a non-DVS scheme is observed.
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A 4-page preliminary version of this work was presented at the IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS) 2005. This work is supported by the Institute for Space Systems Operations.
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Cheng, A.M.K., Wang, Y. A Dynamic Voltage Scaling Algorithm for Dynamic Workloads. J Sign Process Syst Sign Image Video Technol 52, 45–57 (2008). https://doi.org/10.1007/s11265-007-0098-x
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DOI: https://doi.org/10.1007/s11265-007-0098-x