We've been using Server2008R2 with Hyper-V for a couple of years now and chose it at the time because of its ability to make use of Intel SpeedStep and AMD PowerNow! Now with Server 2012 and Hyper-V V3, all power management abilities seem to be gone. The CPUs are always at full speed and our servers need twice the energy as before while idling. (Yes, the CPU P-states are enabled in the BIOS) Is this by design? Is there a workaround to enable cpu power management again? Despite the great new features of Hyper-V 3, this would be a show-stopper for us since we are very concerned about energy consumption.
Have you looked at you power plan settings? I believe if you have it set to High Performance, the CPUs are never parked and therefore always consuming maximum power. Perhaps you can switch to Balanced or a Custom level that allows for power savings features to be enabled.