System information

Power Management 133

Power Management

Power management aims at reducing operating costs for energy and cooling systems

while at the same time keeping the performance of a system at a level that matches

the current requirements. Thus, power management is always a matter of balancing

the actual performance needs and power saving options for a system. Power manage-

ment can be implemented and used at different levels of the system. A set of spec-

ifications for power management functions of devices and the operating system in-

terface to them has been defined in the Advanced Configuration and Power Inter-

face (ACPI). As power savings in server environments can primarily be achieved

on processor level, this chapter introduces some of the main concepts and highlights

some tools for analyzing and influencing relevant parameters.

11.1 Power Management at CPU

Level

At CPU level, you can control power usage in various ways: for example, by using

idling power states (C-states), changing CPU frequency (P-states), and throttling the

CPU (T-states). The following sections give a short introduction to each approach and

its significance for power savings. Detailed specifications can be found at http://