A Work Dependent OS Timing Scheme for Power Management: Implementation in Linux and Modeling of Energy Savings.

We present a Work Dependent Timing (WDT) scheme for the Linux operating system that skips periodic system timer ticks when the system is idle. Our scheme parses the internal lists and queues in Linux to determine when the next work item is due and eliminates “workless” timer ticks that solely update system time. Subsequently, we program the hardware timer with the timeout value of the
nearest work item and then put the processor/system into an optimal low power state. Furthermore, when skipping timer ticks, the opportunity may arise to exploit a more efficient low power system and processor state that would not be possible with a conventional periodic timing scheme because periods where the system can sleep may now exceed the time to transition into and out of the low power state. We describe the implementation of the WDT scheme in detail and discuss its impact on system software. Experimental results with an embedded system verify the ability of the WDT scheme to extend battery life. An analytical power model that quantifies the ability of the scheme to reduce system power consumption is presented. The model is in good agreement with the experimental
results. Also included in the model is a power state selection algorithm which, given full knowledge about the system power levels, transition times and timer events, can dynamically calculate the optimal low power state to exploit at any given time.

By: Claus Michael Olsen, Chandrasekhar Narayanaswami

Published in: RC22784 in 2003


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