IBM has announced their new energy rating system for computer hardware. The rating is driven by hardware monitoring systems for cooling and power consumption and can be read in real time. This looks like a fantastic metric to minimize.
David Anderson PE, IBM green consultant said, “A single mainframe running Linux may be able to perform the same amount of work as approximately 250 x86 processors while using as little as two to ten percent of the amount of energy.”
This is assuming you have a bunch of machines being virtualized on a single mainframe, which means the mainframe is in control of both the hardware monitoring and the scheduling of system resources. Taking thread priority in to account, the scheduler could be redesigned to optimize (local delta rule?) the the energy use instead of responsiveness for lower priority threads. It could even be expanded upon to look at the history of it’s environment and give higher priority to certain virtual machines in times of peak use (Approximations based on posterior).