The FREE HyperV_Mon by Tim Mangan tool helps you to understand Performance characteristics in a Hyper-V world. It now supports Windows 8 Hyper-V, Hyper-V 3.0.
HyperV_Mon monitors physical, logical, and virtual performance information that is available when running virtual machines under Microsoft Hyper-V. The graphical display is organized to help easily understand the CPU performaces being experienced. Detailed text displays also help highlight other performance issues such as memory, paging, and I/O. Additional information is provided about virtualization "overhead" that is detected within the VMs. Newly updated to support Hyper-V R1, R2, and R3 (Windows Server 8); requires .Net 4.0.
Source and download: http://www.tmurgent.com/Tools.aspx