Evaluation of Online Power-Down Algorithms

Power-down mechanisms are well known and are widely used to save energy, these mechanisms are encountered on an everyday basis. We consider a device which has states OFF, ON, and a fixed number of intermediate states. The state of the device can be switched at any time. In the OFF state the device consumes zero energy and in ON state it works at its full power consumption. The intermediate states consume only some fraction of energy proportional to the usage time but switching back to the ON state has different constant setup cost depending on the current state. We give results regarding power consumption to satisfy service request based on online competitive analysis. Competitive ratios, which show the effectiveness of the algorithms compared to the optimal solution, are calculated for systems with up to six states. For two state on-off systems, a decrease and reset algorithm is analyzed experimentally. It is shown that this algorithm has favorable performance for request sequences with high slackness degree.