VMware vSphere vCenter Server 4.0 - Manual (Page 24)

n When you move a virtual machine from one host to another, affinity might no longer apply because the
new host might have a different number of processors.
n The NUMA scheduler might not be able to manage a virtual machine that is already assigned to certain
processors using affinity.
n Affinity can affect an ESX/ESXi host's ability to schedule virtual machines on multicore or hyperthreaded
processors to take full advantage of resources shared on such processors.
CPU Power Management
To improve CPU power efficiency, you can configure your ESX/ESXi hosts to dynamically switch CPU
frequencies based on workload demands. This type of power management is called Dynamic Voltage and
Frequency Scaling (DVFS). It uses processor performance states (P-states) made available to the VMkernel
through an ACPI interface.
ESX/ESXi supports the Enhanced Intel SpeedStep and Enhanced AMD PowerNow! CPU power management
technologies. For the VMkernel to take advantage of the power management capabilities provided by these
technologies, you might need to first enable power management, sometimes referred to as Demand-Based
Switching (DBS), in the BIOS.
To set the CPU power management policy, use the advanced host attribute Power.CpuPolicy. This attribute
setting is saved in the host configuration and can be used again at boot time, but it can be changed at any time
and does not require a server reboot. You can set this attribute to the following values.
static The default. The VMkernel can detect power management features available
on the host but does not actively use them unless requested by the BIOS for
power capping or thermal events.
dynamic The VMkernel optimizes each CPU's frequency to match demand in order to
improve power efficiency but not affect performance. When CPU demand
increases, this policy setting ensures that CPU frequencies also increase.
vSphere Resource Management Guide
24 VMware, Inc.