abstract.tex
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\begin{abstract}
Battery lifetime continues to be a top complaint about smartphones. Dynamic
voltage and frequency scaling (DVFS) has existed for mobile device CPUs for some
time, and provides a tradeoff between energy and performance. Dynamic frequency
scaling is beginning to be applied to memory as well to make more
energy-performance tradeoffs possible.
We present the first characterization of the behavior of the optimal frequency
settings of workloads running both, under \textit{energy constraints} and on
systems capable of CPU DVFS and memory DFS, an environment representative
of next-generation mobile devices. Our results show that continuously using
the optimal frequency settings results in a large number of frequency
transitions which end up hurting performance. However, by permitting a small
loss in performance, transition overhead can be reduced and end-to-end
performance and energy consumption improved. We introduce the idea of
\textit{inefficiency} as a way of constraining task energy consumption
relative to the most energy-efficient settings, and characterize the
performance of multiple workloads running under different inefficiency
settings. Overall our results have multiple implications for next-generation
mobile devices exposing multiple energy-performance tradeoffs.
\end{abstract}