Support policy for CPU Overclocking on VMware ESXi

Products

VMware vSphere ESXi

Issue/Introduction

Administrators inquiring whether CPU overclocking is supported on ESXi hosts.
Users attempting to modify BIOS/UEFI settings to increase CPU frequency beyond manufacturer specifications.
Performance tuning questions regarding running CPUs at higher clock speeds than the base or official Turbo Boost frequency.

Environment

VMware ESXi (all supported versions)
Physical servers listed in the VMware Hardware Compatibility Guide (HCL)

Cause

CPU overclocking is configured at the hardware or firmware level (BIOS/UEFI) and involves operating the CPU beyond its vendor-supported specifications (e.g., increased frequency, multiplier, voltage). ESXi itself does not provide any mechanisms to configure, control, or validate CPU overclocking settings. Running ESXi in an overclocked environment may lead to the following issues:

Purple Screen of Death (PSOD): ESXi kernel panics due to CPU machine check exceptions (MCE) or memory errors caused by unstable voltage or timing.
Time Keeping Issues (Time Drift): Virtualization relies heavily on the CPU's Time Stamp Counter (TSC). Altering the bus speed or multiplier can cause the host clock to drift, leading to time synchronization issues within virtual machines (affecting logs, database transactions, and authentication protocols like Kerberos).
Silent Data Corruption: Instability in the CPU cache or memory controller can result in silent data corruption before it is written to the disk.
Thermal Throttling: Improper cooling solutions for overclocked CPUs may cause the system to throttle aggressively, leading to degraded performance rather than the intended improvement.

Resolution

VMware by Broadcom does NOT support CPU overclocking on ESXi hosts.

ESXi is designed to run on enterprise-grade hardware that adheres to the VMware Compatibility Guide. The hypervisor expects the CPU to operate within the specifications defined by the hardware vendor (e.g., Intel or AMD). Running the CPU at frequencies higher than the manufacturer's specification (Overclocking) is considered an unsupported configuration.

In support cases involving overclocked systems, it may be required to revert the hardware to vendor-default, non-overclocked settings before further troubleshooting.

Recommendations:

Operate CPUs at vendor-supported default specifications
Ensure all hardware configurations comply with the VMware HCL https://compatibilityguide.broadcom.com/
Use supported performance tuning methods, such as BIOS power or performance profiles and ESXi Power Management policies (e.g., High Performance)
Coordinate with the hardware vendor for any performance-related firmware tuning within supported limits