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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.
You can configure a virtual machine that runs on an ESXi host 6.0 and later to have up to 128 virtual
CPUs. A virtual machine cannot have more virtual CPUs than the actual number of logical CPUs on the
host. The number of logical CPUs means the number of physical processor cores or two times that
number if hyperthreading is enabled. For example, if a host has 128 logical CPUs, you can configure the
virtual machine for 128 virtual CPUs.
You configure how the virtual CPUs are assigned in terms of cores and cores per socket. Determine how
many CPU cores you want in the virtual machine, then select the number of cores you want in each
socket, depending on whether you want a single core CPU, dual-core CPU, tri-core CPU, and so on. Your
selection determines the number of sockets that the virtual machine has.
For more information about multicore CPUs, see the vSphere Resource Management documentation.
Change CPU Hot Plug Settings
By default, you cannot add CPU resources to a virtual machine when the virtual machine is turned on.
The CPU hot plug option lets you add CPU resources to a running virtual machine.
The following conditions apply:
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For best results, use virtual machines that are compatible with ESXi 5.0 or later.
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Hot-adding multicore virtual CPUs is supported only with virtual machines that are compatible with
ESXi 5.0 or later.
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Not all guest operating systems support CPU hot add. You can disable these settings if the guest is
not supported.
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To use the CPU hot plug feature with virtual machines that are compatible with ESXi 4.x and later, set
the Number of cores per socket to 1.
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Adding CPU resources to a running virtual machine with CPU hot plug enabled disconnects and
reconnects all USB passthrough devices that are connected to that virtual machine.
vSphere Virtual Machine Administration
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