VMware multicore virtual CPU support lets you control the number of cores per virtual CPU in a virtual machine. This capability lets operating systems with socket restrictions use more of the host CPU’s cores, which increases overall performance.
You can configure how the virtual CPUs are assigned in terms of sockets and cores. For example, you can configure a virtual machine with four virtual CPUs in the following ways
- Four sockets with one core per socket
- Two sockets with two cores per socke
- One socket with four cores per socket
Using multicore virtual CPUs can be useful when you run operating systems or applications that can take advantage of only a limited number of CPU sockets. Previously, each virtual CPU was, by default, assigned to a single-core socket, so that the virtual machine would have as many sockets as virtual CPUs. When you configure multicore virtual CPUs for a virtual machine, CPU hot Add/remove is disabled
The ESXi CPU scheduler can detect the processor topology and the relationships between processor cores and the logical processors on them. It uses this information to schedule virtual machines and optimize performance.
The ESXi CPU scheduler can interpret processor topology, including the relationship between sockets, cores, and logical processors. The scheduler uses topology information to optimize the placement of virtual CPUs onto different sockets to maximize overall cache utilization, and to improve cache affinity by minimizing virtual CPU migrations.
In undercommitted systems, the ESXi CPU scheduler spreads load across all sockets by default. This improves performance by maximizing the aggregate amount of cache available to the running virtual CPUs. As a result, the virtual CPUs of a single SMP virtual machine are spread across multiple sockets (unless each socket is also a NUMA node, in which case the NUMA scheduler restricts all the virtual CPUs of the virtual machine to reside on the same socket.)
