Recently we published a whitepaper describing the VMware Virtual Machine Monitor (VMM) execution modes in vSphere 4.0. The VMM may choose hardware support for virtualization whenever it's available or may choose software techniques for virtualization when hardware support is unavailable or not enabled on the underlying platform. The method chosen by the VMM for virtualizing the x86 CPU and MMU is known as the "monitor mode".
This paper attempts to familiarize our customers with default monitor modes chosen by the VMware VMM for many popular guests running on modern x86 CPUs. Most workloads perform well under these default settings. In some cases the user may want to override the default monitor mode. We provide a few examples in which the user may observe performance benefits in overriding the default monitor modes and two ways by which the user can override the defaults.
The default monitor mode chosen by the VMM for a particular guest depends on the available (or enabled) hardware features on the underlying platform and the guest OS performance in that mode. The difference in the availability of virtualization support on modern x86 CPUs and the guest OS performance when using those features (or when using software techniques when those features are unavailable) leads to a complex problem of choosing the appropriate monitor mode for a given guest on a given x86 CPU. For more details please download and read our full paper from here.