Processor Model

We assume the processor can change its voltage continuously. In other words, a processor can operate at any normalized speed from 0 to 1. When the speed is 0, the processor is in shutdown mode. We shall ignore the speed switching overhead which in general is small [18]. From the Introduction section, we note that P, the power consumed per CPU cycle is proportional to V 2 f, and f is proportional to (V −Vt) 2 /V , where V is the supply voltage, f the frequency, and Vt the voltage threshold. The exact definition of P depends on the specific hardware. We shall not assume any fixed form for P, except that it is a strictly convex function of the frequency. We use P(S) to denote that P is a function of speed S.