On Combining Two Server Control Policies for Energy Efficiency

TL;DR

This paper investigates whether combining server speed scaling and server off/on policies yields energy efficiency benefits, finding that these mechanisms are generally not synergistic and one tends to dominate.

Contribution

The study models the interaction of two server control policies using a Markov chain and concludes that their combined use offers limited additional energy savings.

Findings

Mechanisms are not synergistic across all loads.

One control policy tends to dominate in energy savings.

Limited additional benefit from combining policies.

Abstract

Two popular server control policies are available for reducing energy consumption while maintaining acceptable performance levels: server speed scaling and the ability to turn servers off (and on). In this work, we explore the question of whether there are synergistic effects between these two mechanisms. To do this, we employ a continuous-time Markov chain model where the server can be turned off (and turning the server back on takes some time) and where the speed of the server can take on two values: a nominal operating speed and a reduced operating speed. For a cost function that is linear in the mean response time and server power consumption, we suggest that the mechanisms are not synergistic in that for all system loads, one mechanism is dominant in that if the other mechanism is also employed, there is only a small decrease in cost.