Modeling the energy consumption of programs: Thermal aspects and energy/frequency convexity rule

This article summarizes our current studies aiming at a better understanding of the energy consumption of a microprocessor during the execution of an application through a combination of theoretical results and experimental validations, The analysis of the transient thermal behavior and energy gains (ranging from 20 to 40% in some cases) via the adaptation of the clock frequency are of obvious practical interest. A general Passive Cooling Rule (PCR) for an isothermal object subjected to radiation, convection and internal heat generation is proposed. This power-temperature model is observed on an Exynos 5410 processor. Several approximations to this cooling rule are formulated for practical use, particularly online. They are accompanied by general rules for assessing when passive cooling becomes non-negligible compared to active cooling in embedded systems. On another hand, a theoretical framework for the existence of an Energy/Frequency Convexity Rule (EFCR) of program consumption is established. It is validated both by the state of the art and by experimental measurements. Power consumption models are then explained. The novelty of these models is that they take into account certain characteristics of the program execution and that they can be directly reused in any simulation for other processors of similar architecture.