I just finished up testing for a new whitepaper on Hyper-V performance and one of the initial things I had to figure out was how to measure the CPU utilization on the server. What is known as the parent partition (the initial Windows Server 2008 that is installed on the server and then used to enable the Hyper-V role) does not include the CPU utilization for its VMs in the main Processor Utilization performance counter. This was surprising to me at first, but makes sense when you consider the architecture of Hyper-V. In this architecture, the VMs do not go through the parent partition to access the processors. (Although I/O does to use the device drivers of the parent partition.)

In order to solve this problem Microsoft has created some new performance counters that are specific to the Hyper-V Hypervisor. Early on in the betas for Hyper-V it wasn't clear what these counters did, as I blogged about back in January, but it is now much clearer with some guides from Microsoft.

In order to measure the total CPU utilization on a Windows Server 2008 system running VMs under Hyper-V use the Hyper-V Hypervisor Logical Processor % Total Run Time counter in Performance Monitor (more affectionately known as perfmon). If you just look at the % CPU Utilization or the performance tab of Task Manager you will only see the CPU utilization of the parent partition and not the VMs.

Todd