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 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.