Specify CPU options for an Amazon EC2 instance - Amazon Elastic Compute Cloud
Disable simultaneous multithreadingSpecify a custom number of vCPUs at launchSpecify a custom number of vCPUs in a launch templateChange CPU options

Specify CPU options for an Amazon EC2 instance

You can specify CPU options during or after instance launch through the AWS Management Console, AWS CLI, EC2 API, or SDKs. This page covers the AWS Management Console and AWS CLI methods, as follows.

Disable simultaneous multithreading

To disable simultaneous multithreading (SMT), also known as hyper-threading, specify 1 thread per core.

Console
To disable SMT during instance launch

  1. Follow the Launch an EC2 instance using the launch instance wizard in the console procedure and configure your instance as needed.

  2. Expand Advanced details, and select the Specify CPU options checkbox.

  3. For Core count, choose the number of required CPU cores. In this example, to specify the default CPU core count for an r5.4xlarge instance, choose 8.

  4. To disable SMT, for Threads per core, choose 1.

  5. In the Summary panel, review your instance configuration, and then choose Launch instance. For more information, see Launch an EC2 instance using the launch instance wizard in the console.

AWS CLI
To disable SMT during instance launch

Use the run-instances AWS CLI command and specify a value of 1 for ThreadsPerCore for the --cpu-options parameter. For CoreCount, specify the number of CPU cores. In this example, to specify the default CPU core count for an r5.4xlarge instance, specify a value of 8.

aws ec2 run-instances \
    --image-id ami-1a2b3c4d \
    --instance-type r5.4xlarge \
    --cpu-options "CoreCount=8,ThreadsPerCore=1" \
    --key-name MyKeyPair
Note

To disable SMT for an existing instance, follow the process shown in Change CPU options for your EC2 instance, and change the number of threads that run per core to 1.

Specify a custom number of vCPUs at launch

You can customize the number of CPU cores and threads per core when you launch an instance from the EC2 console or AWS CLI. The examples in this section use an r5.4xlarge instance type, which has the following default settings:

  • CPU cores: 8

  • Threads per core: 2

Instances launch with the maximum number of vCPUs available for the instance type by default. For this instance type, that's 16 total vCPUs (8 cores running 2 threads each). For more information about this instance type, see Memory optimized instances.

The following example launches an r5.4xlarge instance with 4 vCPUs.

Console
To specify a custom number of vCPUs during instance launch

  1. Follow the Launch an EC2 instance using the launch instance wizard in the console procedure and configure your instance as needed.

  2. Expand Advanced details, and select the Specify CPU options checkbox.

  3. To get 4 vCPUs, specify 2 CPU cores and 2 threads per core, as follows:

    • For Core count, choose 2.

    • For Threads per core, choose 2.

  4. In the Summary panel, review your instance configuration, and then choose Launch instance. For more information, see Launch an EC2 instance using the launch instance wizard in the console.

AWS CLI
To specify a custom number of vCPUs during instance launch

Use the run-instances AWS CLI command and specify the number of CPU cores and number of threads in the --cpu-options parameter. You can specify 2 CPU cores and 2 threads per core to get 4 vCPUs.

aws ec2 run-instances \
    --image-id ami-1a2b3c4d \
    --instance-type r5.4xlarge \
    --cpu-options "CoreCount=2,ThreadsPerCore=2" \
    --key-name MyKeyPair

Alternatively, specify 4 CPU cores and 1 thread per core (disable SMT) to get 4 vCPUs:

aws ec2 run-instances \
    --image-id ami-1a2b3c4d \
    --instance-type r5.4xlarge \
    --cpu-options "CoreCount=4,ThreadsPerCore=1" \
    --key-name MyKeyPair

Specify a custom number of vCPUs in a launch template

You can customize the number of CPU cores and threads per core for the instance in a launch template. The examples in this section use an r5.4xlarge instance type, which has the following default settings:

  • CPU cores: 8

  • Threads per core: 2

Instances launch with the maximum number of vCPUs available for the instance type by default. For this instance type, that's 16 total vCPUs (8 cores running 2 threads each). For more information about this instance type, see Memory optimized instances.

The following example creates a launch template that specifies the configuration for an r5.4xlarge instance with 4 vCPUs.

Console
To specify a custom number of vCPUs in a launch template

  1. Follow the Create a launch template by specifying parameters procedure and configure your launch template as needed.

  2. Expand Advanced details, and select the Specify CPU options checkbox.

  3. To get 4 vCPUs, specify 2 CPU cores and 2 threads per core, as follows:

    • For Core count, choose 2.

    • For Threads per core, choose 2.

  4. In the Summary panel, review your instance configuration, and then choose Create launch template. For more information, see Store instance launch parameters in Amazon EC2 launch templates.

AWS CLI
To specify a custom number of vCPUs in a launch template

Use the create-launch-template AWS CLI command and specify the number of CPU cores and number of threads in the CpuOptions parameter. You can specify 2 CPU cores and 2 threads per core to get 4 vCPUs.

aws ec2 create-launch-template \
    --launch-template-name TemplateForCPUOptions \
    --version-description CPUOptionsVersion1 \
    --launch-template-data file://template-data.json

The following is an example JSON file that contains the launch template data, which includes the CPU options, for the instance configuration for this example.

{
    "NetworkInterfaces": [{
        "AssociatePublicIpAddress": true,
        "DeviceIndex": 0,
        "Ipv6AddressCount": 1,
        "SubnetId": "subnet-7b16de0c"
    }],
    "ImageId": "ami-8c1be5f6",
    "InstanceType": "r5.4xlarge",
    "TagSpecifications": [{
        "ResourceType": "instance",
        "Tags": [{
            "Key":"Name",
            "Value":"webserver"
        }]
    }],
    "CpuOptions": {
        "CoreCount":2,
        "ThreadsPerCore":2
    }
}

Alternatively, specify 4 CPU cores and 1 thread per core (disable SMT) to get 4 vCPUs:

{
    "NetworkInterfaces": [{
        "AssociatePublicIpAddress": true,
        "DeviceIndex": 0,
        "Ipv6AddressCount": 1,
        "SubnetId": "subnet-7b16de0c"
    }],
    "ImageId": "ami-8c1be5f6",
    "InstanceType": "r5.4xlarge",
    "TagSpecifications": [{
        "ResourceType": "instance",
        "Tags": [{
            "Key":"Name",
            "Value":"webserver"
        }]
    }],
    "CpuOptions": {
        "CoreCount":4,
        "ThreadsPerCore":1
    }
}

Change CPU options for your EC2 instance

As your needs change over time, you might want to change the configuration of CPU options for an existing instance. Each thread that runs on your instance is known as a virtual CPU (vCPU). You can change the number of vCPUs that run for an existing instance in the Amazon EC2 console, AWS CLI, API, or SDKs. The instance state must be Stopped before you can make this change.

To view console or command line steps, select the tab that matches your environment. For API request and response information, see ModifyInstanceCpuOptions in the Amazon EC2 API Reference.

Console

Follow this procedure to change the number of active vCPUs for your instance from the AWS Management Console.

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the left navigation pane, choose Instances. This opens the list of instances that are defined for the current AWS Region.

  3. Select the instance from the Instances list. Alternatively, you can select the instance link to open the instance detail page.

  4. If the instance is running, you must stop it before you proceed. Choose Stop instance from the Instance state menu.

  5. To change your vCPU configuration, choose Change CPU options from Instance settings in the Actions menu. This opens the Change CPU options page.

  6. Choose one of the following CPU options to change the configuration for your instance.

    None

    This option resets your instance to the default number of vCPUs for your instance type. The default is to run all threads for all CPU cores.

    Specify CPU options

    This option enables configuration of the number of vCPUs that are running on your instance.

  7. If you selected Specify CPU options, the Active vCPU configuration is displayed.

    • The first selector configures the number of threads that run for each CPU core. To disable simultaneous multithreading, you can change the number of threads that run per core to 1.

    • The second selector configures the number of CPUs that are running for your instance.

    The following fields are updated dynamically, as you make changes to the CPU option selectors.

    • Active vCPUs: The number of CPU cores multiplied by the threads per core, based on the selections that you made. For example, if you selected 2 threads and 4 cores, that would equal 8 vCPUs.

    • Total vCPUs: The maximum number of vCPUs for the instance type. For example, for an m6i.4xlarge instance type, this is 16 vCPUs (8 cores running 2 threads each).

  8. To apply your updates, choose Change.

AWS CLI

Follow this procedure to change the number of active vCPUs for your instance from the AWS CLI.

Use the modify-instance-cpu-options AWS CLI command and specify the number of CPU cores that run in the --core-count parameter, and the number of threads that run per core in the --threads-per-core parameter.

The following examples shows two possible configurations on an m6i.4xlarge instance type to run 8 vCPUs on the specified instance. The default for this instance type is 16 vCPUs (8 cores running 2 threads each).

Example 1: Run 4 CPU cores with 2 threads per core, for a total of 8 vCPU.

aws ec2 modify-instance-cpu-options \
    --instance-id i-1234567890abcdef0 \
    --core-count=4 \
    --threads-per-core=2

Example 2: Disable simultaneous multi-threading by changing the number of threads that run per core to 1. The resulting configuration also runs a total of 8 vCPUs (8 CPU cores with 1 thread per core,).

aws ec2 modify-instance-cpu-options \
    --instance-id i-1234567890abcdef0 \
    --core-count=8 \
    --threads-per-core=1