How to reducing the number of cores of ESXi

Products

• VMware vSphere ESXi

Issue/Introduction

Troubleshooting: To aid in troubleshooting, you may need to temporarily reduce the number of cores allocated to ESXi.

Important Licensing Reminder:

• All cores on the server where the software is installed must be licensed, including any cores deactivated in the BIOS.
• The total number of core licenses required must match the number of physical cores on the server.

Warning: This knowledge base article (KB) must not be used in production environments, as doing so violates Broadcom's licensing policy. For more information, refer to Broadcom's official licensing terms:
VMware Cloud Foundation (VCF) SPD – Broadcom

Resolution

There are 2 options to reduce the amount of cores presented to ESXi.

1. Check with your hardware vendor if the Cores can be disabled from the BIOS/EFI

2. From the host client or vCenter.
- Go to Configure>System>Advanced System Settings
- Click on Edit
- Search for VMkernel.Boot.max.PCPUS
- Change the default value 1024 to the desired Value
- You need to reboot the host to apply the new setting.



You can also change this value with SSH or PowerCLI:

SSH:
[root@esxi701:~] esxcli system settings kernel set -s maxPCPUS -v 6
[root@esxi701:~] esxcli system settings kernel list -o maxPCPUS
Name      Type    Configured  Runtime  Default  Description
--------  ------  ----------  -------  -------  -----------
maxPCPUS  uint32  6           1024     1024     Number of PCPUs vmkernel should use.

PowerCLI:


Example:
If your host has 2 CPUs with 6 Cores per Socket, setting the value to 6 will disable 1 CPU.

Before:



After: