6.7

n
Affinity can interfere with the ESXi host’s ability to meet the reservation and shares specified for a
virtual machine.
n
Because CPU admission control does not consider affinity, a virtual machine with manual affinity
settings might not always receive its full reservation.
Virtual machines that do not have manual affinity settings are not adversely affected by virtual
machines with manual affinity settings.
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 the host's ability to schedule virtual machines on multicore or hyperthreaded
processors to take full advantage of resources shared on such processors.
Host Power Management Policies
You can apply several power management features in ESXi that the host hardware provides to adjust the
balance between performance and power. You can control how ESXi uses these features by selecting a
power management policy.
Selecting a high-performance policy provides more absolute performance, but at lower efficiency and
performance per watt. Low-power policies provide less absolute performance, but at higher efficiency.
You can select a policy for the host that you manage by using the VMware Host Client. If you do not
select a policy, ESXi uses Balanced by default.
Table 4‑1. CPU Power Management Policies
Power Management Policy Description
High Performance Do not use any power management features.
Balanced (Default) Reduce energy consumption with minimal performance
compromise
Low Power Reduce energy consumption at the risk of lower performance
Custom User-defined power management policy. Advanced configuration
becomes available.
When a CPU runs at lower frequency, it can also run at lower voltage, which saves power. This type of
power management is typically called Dynamic Voltage and Frequency Scaling (DVFS). ESXi attempts to
adjust CPU frequencies so that virtual machine performance is not affected.
When a CPU is idle, ESXi can apply deep halt states, also known as C-states. The deeper the C-state,
the less power the CPU uses, but it also takes longer for the CPU to start running again. When a CPU
becomes idle, ESXi applies an algorithm to predict the idle state duration and chooses an appropriate C-
state to enter. In power management policies that do not use deep C-states, ESXi uses only the
shallowest halt state for idle CPUs, C1.
vSphere Resource Management
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