When a virtual machine is powered on, ESXi assigns it a home node. A virtual machine runs only on processors within its home node, and its newly allocated memory comes from the home node as well.
Unless a virtual machine’s home node changes, it uses only local memory, avoiding the performance penalties associated with remote memory accesses to other NUMA nodes.
When a virtual machine is powered on, it is assigned an initial home node so that the overall CPU and memory load among NUMA nodes remains balanced. Because internode latencies in a large NUMA system can vary greatly, ESXi determines these internode latencies at boot time and uses this information when initially placing virtual machines that are wider than a single NUMA node. These wide virtual machines are placed on NUMA nodes that are close to each other for lowest memory access latencies.
Initial placement-only approaches are usually sufficient for systems that run only a single workload, such as a benchmarking configuration that remains unchanged as long as the system is running. However, this approach is unable to guarantee good performance and fairness for a datacenter-class system that supports changing workloads. Therefore, in addition to initial placement, ESXi 5.0 does dynamic migration of virtual CPUs and memory between NUMA nodes for improving CPU balance and increasing memory locality.
