Several solutions are considered to reduce energy consumption of computers. Among them, Dynamic Voltage and Frequency Scaling (DVFS) emerged as an effective way to enhance energy efficiency by adapting processor frequency to workloads.We propose FoREST, a new DVFS controller designed to efficiently exploit the recent technologies introduced in processors. FoREST is a runtime DVFS controller able to estimate the energy savings it can achieve from power gains, evaluated offline using power probes embedded in modern CPUs, and speedups measured at runtime for the current workload. It does not use any performance model but rather directly measures the effect of frequency transitions on energy. Using such methodology, FoREST can achieve energy savings on the whole system under user-defined slowdown constraints.In our experiments, FoREST is able to achieve more than 39% CPU energy savings compared to the default Linux DVFS controller, with a slowdown below 5%, as requested by the user.

Understanding and controlling program behavior is a challenging objective for the design of advanced compilers and critical system development. In this paper, we propose an analysis and modeling strategy of program behavior characteristics by considering traces generated from opportune code instrumentation. The proposed models consist in periodic and linear interpolations separated into adjacent program phases. It is shown that these models exhibit apparent and useful information on program behavior. Moreover they can directly be used to guide static optimizations or to build dynamic optimization processes as it is shown for the implementation of efficient dynamic data prefetching processes for some benchmark programs.

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