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This paper presents a family of Rate-Harmonized Schedulers that can be used in reservation-based operating systems to naturally cluster task execution and lump processor idle durations. While traditional approaches to energy management have focused on reducing dynamic switching power through Dynamic Voltage and Frequency Scaling (DVFS), processor technology trends predict a future in which static leakage power will begin to dominate. To this end, most modern processors provide built-in support for sleep modes with low leakage power. However, substantial time is required to switch in/out of such sleep modes due to mechanical oscillator stabilization delays. Significant opportunities for energy saving are potentially missed due to idle gaps between executing tasks that are shorter than the time required to enter the sleep mode. Armed with apriori workload information, reservation-based operating systems can potentially eliminate such wasted idle durations using Rate-Harmonized Scheduling. An Energy-Saving Rate-Harmonized Scheduler guarantees that every idle duration can be used to switch into sleep mode. This paper also provides extensions to Rate-Harmonized Scheduling to support multicore processors. Empirical evaluation results are provided from an implementation in the nano-RK operating system for wireless sensor networks. Energy-Saving Rate-Harmonized Scheduling saves 16.8% energy compared to conventional Rate-Monotonic Scheduling for the task set used in Sensor Andrew project. At low utilization levels, Energy-Saving Rate-Harmonized Scheduling can save up to 39% energy on randomly generated task sets.
Date of Publication: Aug. 2010