Compiler driven energy efficiency

44■ The Green Computing Book: Tackling Energy Efficiency at Large Scale conservation can be achieved in the hardware by various mechanisms, like dynamic voltage and frequency scaling [1], state transitions among various power states, or temporarily turning off some resources when they are not being used. Hardware enhancements for energy optimization have been reasonably well studied in the past. However, energy optimizations cannot leverage these hardware mechanisms without adequate support from the system software. Software like the compiler, operating system, and runtime systems can act asenablersfor these energy-conserving mechanisms to be used effectively. Without these enablers, hardware optimizations alone cannot accrue the predicted energy benefits. In particular, the compiler is capable of automatically analyzing program behavior, data access patterns, and resource requirements of complex application programs. An energy-aware compiler can reshape a program either explicitly, by inserting instructions to turn off resources that are not used, or implicitly, by increasing the idle periods between two usages of the resource. A compiler framework is the ideal platform for performing such energy-aware transformations automatically. For example, the efficacy of previously proposed energy optimization techniques like dynamic disk speed modulation (dynamic rotations per minute, DRPM)[2] depend on the availability of idle disk usage periods. Ifwe execute unmodified code or code optimized for high performance, it has been observed [3] that the opportunity for finding such idle periods is diminished. Energy-aware …