Bottlerocket: Is disabling hyperthreading possible?

[malodie]

We have a use case for disabling hyperthreading, but we use bottlerocket for all EKS nodes. Is it possible to disable hyperthreading through the settings?

https://aws.amazon.com/blogs/compute/disabling-intel-hyper-threading-technology-on-amazon-linux/
This is the most relevant blog to what we're trying to achieve.

I do not see any relevant settings in the bottlerocket user data settings, but I could just be missing the appropriate setting.
https://github.com/bottlerocket-os/bottlerocket?tab=readme-ov-file#using-user-data

[bcressey]

You could use settings.boot.kernel-parameters and maxcpus=N (where N is half the total CPUs) or perhaps nosmt to accomplish this.

I'd probably combine this with a bootstrap container to calculate the value dynamically, if you're using a variety of instance types, and enable settings.boot.reboot-to-reconcile to reboot into the new configuration.

EC2 lets you specify CPU options at launch for a distro-agnostic way to configure it.

Finally, the aarch64 / Graviton instance types don't use hyperthreading at all, so you could use those instead.