Potential Issues with CPU Affinity

Before you use CPU affinity, you might need to consider certain issues.

Potential issues with CPU affinity include:

• For multiprocessor systems, ESXi systems perform automatic load balancing. Avoid manual specification of virtual machine affinity to improve the scheduler’s ability to balance load across processors.
• Affinity can interfere with the ESXi host’s ability to meet the reservation and shares specified for a virtual machine.
• Because CPU admission control does not consider affinity, a virtual machine with manual affinity settings might not always receive its full reservation.

  Virtual machines that do not have manual affinity settings are not adversely affected by virtual machines with manual affinity settings.

• When you move a virtual machine from one host to another, affinity might no longer apply because the new host might have a different number of processors.
• The NUMA scheduler might not be able to manage a virtual machine that is already assigned to certain processors using affinity. For more information, see Using NUMA Systems with ESXi.
• Affinity can affect the host's ability to schedule virtual machines on multicore or hyperthreaded processors to take full advantage of resources shared on such processors.