6.7

Specifying CPU Configuration
You can specify CPU configuration to improve resource management. However, if you do not customize
CPU configuration, the ESXi host uses defaults that work well in most situations.
You can specify CPU configuration in the following ways:
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Use the attributes and special features available through the vSphere Client. The vSphere Client
allows you to connect to the ESXi host or a vCenter Server system.
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Use advanced settings under certain circumstances.
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Use the vSphere SDK for scripted CPU allocation.
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Use hyperthreading.
Multicore Processors
Multicore processors provide many advantages for a host performing multitasking of virtual machines.
Note In this topic, "Memory" can refer to physical RAM or Persistent Memory.
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.
vSphere Resource Management
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