A feedback control approach to dynamic speed scaling in computing systems

Speed scaling concerns the dynamic adaptation of the active service capacity of a computing system to the processing demands. This problem has received recent attention, motivated by balancing performance with energy consumption; various proposals have been suggested where the processor speed is a function of the current job population, combined with an appropiate scheduling discipline. In this paper we cast the problem in the setting of feedback control, using a fluid model of the queueing system; in this framework the problem is of designing a controller to track the exogenous demand, and the prior work can be seen as restricting the controller to a static function. By allowing for a dynamic controller, in particular a proportional-integral law, we show how the relevant performance tradeoff can be improved. We further indicate a discrete server implementation of this control law, based on a mix of dedicated servers and pooled helpers; its performance is evaluated analytically and by simulation.