The EVC mode of a virtual machine defines the CPU features that the virtual machine can access. The virtual machine's EVC mode is determined when it is powered on in an EVC-enabled cluster.
When a virtual machine is powered on, it determines the EVC mode of the cluster in which it is running. If the EVC mode of the cluster is later raised, the virtual machine does not change its EVC mode until it is powered off and powered on again. This means that the virtual machine does not use any CPU features exposed by the cluster's new EVC mode until the virtual machine has been powered off and powered on again.
For example, consider a cluster containing hosts with Intel Xeon 45 nm Core two processors that have been set to the Intel Merom Generation (Xeon Core 2) EVC mode. A virtual machine powered on in this cluster runs in the Intel Merom Generation (Xeon Core 2) EVC mode. If the cluster's EVC mode is raised to Intel Penryn Generation (Xeon 45 nm Core 2), the virtual machine remains at the lower Intel Merom Generation (Xeon Core 2) EVC mode. To use any of the features exposed by the higher cluster EVC mode, such as SSE4.1, you must power off the virtual machine and power it on again.
