The manual configuration for cores per socket for Virtual Machine might result in reduced performance

Products

• VMware vSphere ESXi 8.0

Issue/Introduction

• When setting cores per socket for Virtual Machine manually will prompt following warning:
  
   The manual configuration for cores per socket might result in reduced performance.
  
  
•  An optimal CPU topology is applied by default at the initial power-on of the VM; the configuration also persists when the VM is migrated with
  vMotion.

Environment

VMware vSphere 8.x 

Cause

The vSphere administrator changed the CPU topology setting for Virtaul Machine.

Resolution

To resolve the situation described and prevent any potential performance impact, you can take one of the following actions:

• Revert the cores-per-socket setting to its default,

or

• Proceed with the advanced configuration, keeping in mind the considerations outlined below:
  
  Guest operating system schedulers and applications often optimize workloads according to the underlying hardware topology. In some cases, these optimizations place worker threads within the same socket and avoid migrating threads across sockets to reduce latency caused by cross-socket memory access. For larger VMs (for example, those configured with 32 vCPUs), the default configuration of one core per socket may not be ideal or practical depending on the system design.

This behavior has been observed across a wide range of workloads, including large-scale databases, enterprise applications, and micro-benchmark tests.

Additional Information

VMware vSphere 8.0 Virtual Topology  - Performance Study

Configure Virtual Machine CPU Resources