  This paper provides both theoretical and experimental evidence for the
existence of an Energy/Frequency Convexity Rule, which relates energy
consumption and CPU frequency on mobile devices. We monitored a typical
smartphone running a specific computing-intensive kernel of multiple nested
loops written in C using a high-resolution power gauge. Data gathered during a
week-long acquisition campaign suggest that energy consumed per input element
is strongly correlated with CPU frequency, and, more interestingly, the curve
exhibits a clear minimum over a 0.2 GHz to 1.6 GHz window. We provide and
motivate an analytical model for this behavior, which fits well with the data.
Our work should be of clear interest to researchers focusing on energy usage
and minimization for mobile devices, and provide new insights for optimization
opportunities.

Other Computer Science