6.5.1

Resource sharing Shares specify the relative priority or importance of a virtual machine or
resource pool. If a virtual machine has twice as many shares of a resource
as another virtual machine, it is entitled to consume twice as much of that
resource when the two virtual machines are competing for resources.
Resource allocation You can change CPU resource allocation settings, such as shares,
reservation, and limit, when available resource capacity does not meet
demands. For example, if at year end, the workload on accounting
increases, you can increase the accounting resource pool reserve.
vSphere Virtual
Symmetric
Multiprocessing (Virtual
SMP)
Virtual SMP or vSphere Virtual Symmetric Multiprocessing is a feature that
enables a single virtual machine to have multiple processors.
Virtual CPU Limitations
The maximum number of virtual CPUs that you can assign to a virtual machine is 128. The number of
virtual CPUs depends on the number of logical CPUs on the host, and the type of guest operating system
that is installed on the virtual machine.
Be aware of the following limitations:
n
A virtual machine cannot have more virtual CPUs than the number of logical cores on the host. The
number of logical cores is equal to the number of physical cores if hyperthreading is disabled or two
times that number if hyperthreading is enabled.
n
Not every guest operating system supports Virtual SMP, and guest operating systems that support
this functionality might support fewer processors than are available on the host. For information about
Virtual SMP support, see the VMware Compatibility Guide at
http://www.vmware.com/resources/compatibility.
n
Hyperthreaded hosts might affect virtual machine performance, depending on the workload. The best
practice is to test your workload to determine whether to enable or disable hyperthreading on your
hosts.
Configuring Multicore Virtual CPUs
VMware multicore virtual CPU support lets you control the number of cores per virtual socket in a virtual
machine. This capability lets operating systems with socket restrictions use more of the host CPU's cores,
which increases overall performance.
Important When you configure your virtual machine for multicore virtual CPU settings, you must ensure
that your configuration complies with the requirements of the guest operating system EULA.
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.
vSphere Virtual Machine Administration
VMware, Inc. 99