I wrote an SMP API once, and while its fully implemented still in the OS, it won't work right because we changed C API to MUSL and it enables/disables locks internally by counting up/down number of threads. So, that means you cant use it at the moment.

It looks like this: https://github.com/hioa-cs/IncludeOS/blob/dev/api/smp

With that you can schedule work to CPUs directly.

The idea is that things you would normally get from an OS are now libraries that are compiled into your application. If you want a scheduled, you compile it in. If you want a TCP stack, you compile it in.