Q: I'm looking at my Hyper-V server in Task Manager, and the current processor speed is always the same as the maximum speed. Does this mean the processor power management features don't work with Hyper-V?
A: If you look at a normal, non-virtualized host operating system such as Windows 8.1 or Windows Server 2012 R2 in Task Manager, you'll see a speed and a maximum speed. Under light loads, the speed of the processor is decreased to reduce power consumption—which would appear in Task Manager. After the Hyper-V role is enabled, the Speed and Maximum speed settings are always the same, as the following figure shows.
Although it makes sense to assume that Hyper-V is disabling the processor power management, this isn't the case. What's actually happening is that the parent partition (the host OS) is running on top of the hypervisor and therefore no longer has insight into the processor performance states. To obtain this information, you need to use Performance Monitor to view the Hyper-V Hypervisor Logical Processor counter sets. Notice in the figure below that my processors are in C1 state more than 90 percent of the time. (C1 is a power saving mode.)