Practical PACE for embedded systems

In current embedded systems, one of the major concerns is energy conservation. The dynamic voltage-scheduling (DVS) framework, which involves dynamically adjusting the voltage and frequency of the CPU, has become a well studied technique. It has been shown that if a task's computational requirement is only known probabilistically, there is no constant optimal speed for the task and the expected energy consumption is minimized by gradually increasing speed as the task progresses citelorchsmith. It is possible to find the optimal speed schedule if we assume continuous speed and a well defined power function, which are assumptions that do not hold in practice. In this paper, we study the problem from a practical point of view, that is, we study the case of discrete speeds and make no restriction on the form of the power functions. Furthermore, we take into account processor idle power and speed change overhead, which were ignored in previous similar studies. We present a fully polynomial time approximation scheme (FPTAS), which has performance guarantees and usually obtains solutions very close to the optimal solution in practice. Our evaluation shows that our algorithm performs very well and generally obtains solutions within 0.1.

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