Energy Efficient Prefetching and Caching

Traditional disk management strategies--prefetching and caching in particular--are designed to maximize performance. In mobile systems they conflict with strategies that attempt to save energy by powering down the disk when it is idle. We present new rules for prefetching and caching that maximize power-down opportunities (without performance loss) by creating an access pattern characterized by intense bursts of activity separated by long idle times. We also describe an automatic system that monitors past application behavior in order to generate appropriate prefetching hints, and a general system of kernel enhancements that coordinate I/O activity across all running applications.

We have implemented our system in the Linux kernel, and have measured its performance and energy consumption via physical instrumentation of a running laptop. We describe our implementation and present quantitative results. For workloads including a mix of sequential access to large files (multimedia), concurrent access to large numbers of files (compilation), and random access to large files (speech recognition), we report disk energy savings of 60-80%, with negligible loss in throughput or interactive responsiveness.