Performance By Design

In this blog entry, I want to step back and revisit a topic I have blogged about much earlier ( see  https://performancebydesign.blogspot.com/search/label/VMware . ) and discuss how guest machine performance counters are impacted by virtualization in general. Based on those impacts, we can assess which performance measurements guest machines produce remain viable for diagnosing performance problems and understanding capacity issues. Depending on the type of performance counter, the impact of the virtualization environment varies considerably. To begin, it is necessary to understand how both Hyper-V and the VMware ESX hypervisor affect the clocks and timers that are available on their guest machines. Essentially, Hyper-V intercepts all calls made from the guest OS to access hardware-based clock and timer services on the Host machine and substitutes a virtualized Time of Day clock value. The hypervisor takes pains to ensure that this virtual clock value sent to the guest is minim...