To specify the CPU options for your instance, be aware of the following rules:
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You can't specify CPU options for bare metal instances.
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You can specify CPU options both during and after instance launch.
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To configure CPU options, you must specify both the number of CPU cores and threads per core in the request. For example requests, see Specify CPU options for an Amazon EC2 instance.
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The number of vCPUs for the instance is the number of CPU cores multiplied by the threads per core. To specify a custom number of vCPUs, you must specify a valid number of CPU cores and threads per core for the instance type. You cannot exceed the default number of vCPUs for the instance. For more information, see Supported CPU options for Amazon EC2 instance types.
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To disable simultaneous multithreading (SMT), also referred to as hyper-threading, specify one thread per core.
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In the console, when you change the instance type of an existing instance, Amazon EC2 applies the CPU option settings from the existing instance to the new instance, if possible. If the new instance type doesn't support those settings, the CPU options are reset to None. This option uses the default number of vCPUs for the new instance type.
To update settings for the new instance, select Specify CPU options under Advanced details in the Change instance type view.
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The specified CPU options persist after you stop, start, or reboot an instance.
