Calculating Virtual CPUs

This blog will help you to understands the difference between PCPUs, LCPUs, vCPUs.

When HT is not present or not enabled called A singled physical CPU core (PCPU)
When HT is present and Enabled called A single logical CPU core (LCPU)

As per VMware PCPU and LCPU both same.

Example 1:

If a host has two eight core processors and HT is not present or not enabled, that host has 16 physical CPUs (8 Cores x 2 processors = 16 PCPUs)

Example 2:

If a host has two eight cores and HT enabled, that host has 32 Logical CPUs.

(8 Cores x 2 processors x 2 threads per core = 32 LCPUs)

In virtual machine, processors are referred to as virtual CPUs (vCPUs). When an administrator adds vCPUs to a virtual machine, each of those vCPUs is assigned to pCPU and also actual pCPU may not always be the same.

How to Calculate vCPUs:

For better virtual machine performance (3: 1) or (5:1) = (3 vCPUs: 1 pCPU) or (5 vCPUs: 1 pCPU)

In vSphere 5.0, there is a maximum of 25 vCPUs per physical core. It means the ratio is 25:1.

If the ratio (3 vCPUs per 1 pCPU)

From example 1: ESXi have 16 PCPUs, if the ratio is 3:1; the total vCPUs is 16*3 = 48 vCPUs.

From example 2: ESXi have 32 LCPUs, if the ratio is 3:1; the total vCPUs is 32*3 = 96 vCPUs.

If the ratio (5 vCPUs per 1 pCPU)

From example 1: ESXi have 16 PCPUs, if the ratio is 5:1; the total vCPUs is 16*5 = 80 vCPUs.

From example 2: ESXi have 32 LCPUs, if the ratio is 5:1; the total vCPUs is 32*5 = 160 vCPUs.

Note: In vSphere 5.0, there is a maximum of 25 vCPUs per physical core and administrators can allocate up to 2,048 vCPUs to virtual machines on a single host.