This is one of the hardest parts of working with performance monitoring for virtualization – translating virtual CPU calls to physical ones. In general, most virtualization platforms attempt to pass CPU calls directly through to the underlying host physical processors. This helps reduce latency, although it does cause potential compatibility issues. In order to truly differentiate between guest and host CPU activity, you'll need information from the virtualization layer / Hypervisor. For example, Microsoft Virtual Server includes performance counters that can be used to collect data about individual VMs. (There might be an analogous method in the VMware world, but I'm not aware of the details.)
Below is a table that includes some common counters that I tend to use. In addition, when you install Virtual Server on a machine, you'll have to know objects for use. I believe they're Virtual Machine Processor and Virtual Machine Memory (I'm unable to confirm). If you need more specific information, I recommend you post to an online forum such as the Microsoft Communities site. Perhaps one of the experts in the virtualization-related forums will be able to provide you with more details. Good luck!
| Object | Counter | Instances | Notes |
| Memory | Pages/sec | None | Indicates the total number of paging operations that must access the disk (also known as "hard" page faults); A high value might indicate that memory is a bottleneck |
| Available MBytes | None | Total amount of physical memory available on the computer | |
| Processor | Percent processor time | Total or individual CPUs | Shows overall CPU utilization |
| Interrupts / sec | Total or individual CPUs | Shows the number of hardware-related interrupts managed by the CPU | |
| Process | Percent processor time | All running processes | Can be used to isolate resources used by specific processes |
| IO data bytes / sec | All running processes | Shows the amount of disk IO per process | |
| Page faults / sec | All running processes | Shows amount of paging per process; Might indicate that more physical memory would increase performance |
This was first published in October 2007