Multicore processors provide many advantages for a host performing multitasking of virtual machines.
Intel and AMD have developed processors which combine two or more processor cores into a single integrated circuit (often called a package or socket). VMware uses the term socket to describe a single package which can have one or more processor cores with one or more logical processors in each core.
A dual-core processor, for example, provides almost double the performance of a single-core processor, by allowing two virtual CPUs to run at the same time. Cores within the same processor are typically configured with a shared last-level cache used by all cores, potentially reducing the need to access slower main memory. A shared memory bus that connects a physical processor to main memory can limit performance of its logical processors when the virtual machines running on them are running memory-intensive workloads which compete for the same memory bus resources.
Each logical processor of each processor core is used independently by the ESXi CPU scheduler to run virtual machines, providing capabilities similar to SMP systems. For example, a two-way virtual machine can have its virtual processors running on logical processors that belong to the same core, or on logical processors on different physical cores.
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. This optimization can maximize overall cache usage, and to improve cache affinity by minimizing virtual CPU migrations.
