Simultaneous multithreading (SMT), which is known on Intel processors as Hyper-Threading Technology (HTT), lets a CPU core run as two hardware multithreads. On Compute Engine, each virtual CPU (vCPU) is implemented as a single hardware multithread, and two vCPUs share each physical CPU core by default.
Compute Engine lets you manually set the value for the number of threads per core. For example, workloads with the following concerns might benefit from disabling SMT (setting the number of threads per core to 1):
Performance: Reducing the number of threads that run on each physical CPU core can help improve the performance of workloads that are highly-parallel or that perform floating point calculations.
Security: If a VM runs untrusted code, reducing the number of threads per core can help mitigate CPU vulnerabilities such as Microarchitectural Data Sampling.
Licensing: Some licensing agreements have requirements related to the number of vCPUs that you consume. Reducing the number of threads per core from 2 to 1 might reduce your licensing costs. For more information, consult your licensing agreement.
For many general computing tasks or tasks that require lots of I/O, SMT can increase application throughput significantly. For compute-bound jobs in which both virtual cores are compute-bound, SMT can hinder overall application performance and can add unpredictable variance to jobs. In this case, turning off SMT allows more predictable performance and can decrease job times.
Limitations
You cannot set the number of threads per core on VMs for the following machine types:
- All C4A machine types
- All H3 machine types
- All Tau T2A machine types
- All Tau T2D machine types
- Machine types that have fewer than 2 vCPUs, for example,
n1-standard-1
- Shared-core machine
types, such as
e2-small
.
For C3 and X4 bare metal instances, the number of hyperthreads you have access to is equivalent to the number of hyperthreads on the machine.
In the Google Cloud console, when the number of threads per core is set to 1, the CPU utilization metric can only scale up to a maximum of 50%. When the number of threads per core is set to 2, the CPU utilization metric can scale up to 100%.
Pricing
You are billed for the number of vCPUs defined by a VM's machine type, not the
number of threads that run on each core. For example, the n2-standard-8
machine type can run up to 8 vCPUs, which is 2 vCPUs for each of the 4 physical
CPU cores. If, with the n2-standard-8
machine type, you decide to only run 1
thread per core—effectively 4 vCPUs—you are still billed for 8
vCPUs. For more information about how you are billed for VMs, see VM instance
pricing.
Change the number of threads per core during VM creation
To change the number of threads per core during VM creation, use the Google Cloud console, the gcloud CLI, or the Compute Engine API.
Permissions required for this task
To perform this task, you must have the following permissions:
- All permissions required to create a new VM
Console
To change the number of threads per core during VM creation, use the following Google Cloud console procedure:
In the Google Cloud console, go to the Create an instance page.
In the Name field, enter a name for the VM.
Choose a Region and a Zone for the VM.
Choose a Machine family and a supported Machine type.
Click Advanced configurations to expand the section.
In vCPUs to core ratio, choose the number of threads per core.
Finish configuring other settings for the VM and click Create.
gcloud
To change the number of threads per core during VM creation, use the
gcloud compute instances create
command.
Before using any of the command data below, make the following replacements:
- VM_NAME: the name for the new VM.
- ZONE: the zone for the new VM.
- MACHINE_TYPE: the machine type for the new VM. Must be a machine type with 2 or more vCPUs.
- THREADS_PER_CORE: the number of threads per physical core. Set to either
2
or1
.
Execute the following command:
Linux, macOS, or Cloud Shell
gcloud compute instances create VM_NAME \ --zone=ZONE \ --machine-type=MACHINE_TYPE \ --threads-per-core=THREADS_PER_CORE
Windows (PowerShell)
gcloud compute instances create VM_NAME ` --zone=ZONE ` --machine-type=MACHINE_TYPE ` --threads-per-core=THREADS_PER_CORE
Windows (cmd.exe)
gcloud compute instances create VM_NAME ^ --zone=ZONE ^ --machine-type=MACHINE_TYPE ^ --threads-per-core=THREADS_PER_CORE
You should receive a response similar to the following:
Created [https://www.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/VM_NAME]. NAME: VM_NAME ZONE: ZONE MACHINE_TYPE: MACHINE_TYPE PREEMPTIBLE: INTERNAL_IP: EXTERNAL_IP EXTERNAL_IP: INTERNAL_IP STATUS: RUNNING
REST
To change the number of threads per core during VM creation, use the
instances.insert
method with the
threadsPerCore
field.
Before using any of the request data, make the following replacements:
- PROJECT_ID: the project ID.
- ZONE: the zone for the new VM.
- MACHINE_TYPE: the machine type for the new VM. Must be a machine type with 2 or more vCPUs.
- VM_NAME: the name for the new VM.
- THREADS_PER_CORE: the number of threads per physical core. Set to either
2
or1
.
HTTP method and URL:
POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances
Request JSON body:
{ "machineType": "projects/PROJECT_ID/zones/ZONE/machineTypes/MACHINE_TYPE", "name": "VM_NAME", "advancedMachineFeatures": { "threadsPerCore": THREADS_PER_CORE }, "disks": [ { "type": "PERSISTENT", "boot": true, "initializeParams": { "sourceImage": "projects/debian-cloud/global/images/family/debian-11" } } ], "networkInterfaces": [ { "network": "global/networks/default" } ] }
To send your request, expand one of these options:
You should receive a JSON response similar to the following:
{ "kind": "compute#operation", "id": "7334609091572405391", "name": "operation-1663806045894-5e939085735d8-7499db32-c12fcc03", "zone": "https://www.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE", "operationType": "insert", "targetLink": "https://www.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/VM_NAME", "targetId": "1226375378512516273", "status": "RUNNING", "user": "EMAIL_ADDRESS", "progress": 0, "insertTime": "2022-09-21T17:20:48.751-07:00", "startTime": "2022-09-21T17:20:48.751-07:00", "selfLink": "https://www.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/operations/operation-1663806045894-5e939085735d8-7499db32-c12fcc03" }
Change the number of threads per core on a VM
To change the number of threads per core on a VM, use the Google Cloud console, the gcloud CLI, or the Compute Engine API.
Permissions required for this task
To perform this task, you must have the following permissions:
-
compute.instances.get
on the project -
compute.instances.update
on the project
Console
To change the number of threads per core on an existing VM, use the following Google Cloud console procedure:
In the Google Cloud console, go to the VM instances page.
Click the Name of the VM.
If the VM's Status is Running, click Stop.
Click Edit.
Click Advanced configurations to expand the section.
In the vCPUs to core ratio drop-down list, choose the number of threads per core.
Click Save.
gcloud
To change the number of threads per core on an existing VM, do the following:
Export the properties of the VM by using the following
gcloud compute instances export
command:gcloud compute instances export VM_NAME \ --destination=YAML_FILE_PATH \ --zone=ZONE
Replace the following:
VM_NAME
: the name of the VM from which to export propertiesYAML_FILE_PATH
: the path and file name of a .yaml file in which to save the exported configuration dataZONE
: the zone that contains the VM
In the VM configuration file that was saved in FILE_PATH, update the value for
threadsPerCore
. If the value is not in the file, add the following:advancedMachineFeatures: threadsPerCore: THREADS_PER_CORE
Update the VM with the new count of threads per core by using the following
gcloud compute instances update-from-file
command:gcloud compute instances update-from-file VM_NAME \ --source=FILE_PATH \ --most-disruptive-allowed-action=RESTART \ --zone=ZONE
Replace the following:
VM_NAME
: the name of the VM to updateFILE_PATH
: the path to the updated VM configuration fileZONE
: the zone that contains the VM to update
REST
To change the number of threads per core on an existing VM, use the
following instances.update
method:
PUT https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/VM_NAME?most_disruptive_allowed_action=RESTART { ... "advanced_machine_features": { ... "threadsPerCore": "THREADS_PER_CORE" }, ... }
Replace the following:
PROJECT_ID
: the ID of the projectZONE
: the zone that contains the VMVM_NAME
: the name of the VM from which to export propertiesTHREADS_PER_CORE
: the number of threads per core
View the number of threads per core
To view the number of threads per core, use the procedure that corresponds to the OS that is running on the VM.
Linux
To view the number of threads per core on Linux-based VMs, use the following procedure:
Run the
lscpu
command.lscpu
Review the output to view the number of threads per core.
In the following sample output from an
n2-standard-16
machine, the value for the number of threads per core is1
as shown in theThread(s) per core
line.... CPU(s): 8 On-line CPU(s) list: 0-7 Thread(s) per core: 1 Core(s) per socket: 8 Socket(s): 1 NUMA node(s): 1 Vendor ID: GenuineIntel CPU family: 6 Model: 85 Model name: Intel(R) Xeon(R) CPU @ 2.80GHz ...
Windows
To view the number of threads per core on Windows-based VMs, use the following procedure:
Launch Powershell.
Run the following command.
Get-WmiObject -Class Win32_processor | Select-Object NumberOfCores, @{Name="Thread(s) per core";Expression={$_.NumberOfLogicalProcessors/$_.NumberOfCores}}
Review the output to view the number of threads per core.
In the following sample output from an
n2-standard-16
machine, the value for the number of threads per core is1
as shown in theThread(s) per core
column.NumberOfCores Thread(s) per core ------------- ------------------ 8 1
What's next
- Learn about the operating systems that you can run on Compute Engine VMs.