Tokio specifically says not to use it for CPU intensive tasks and rayon would be better for this: https://tokio.rs/tokio/tutorial

Speeding up CPU-bound computations by running them in parallel on several threads. Tokio is designed for IO-bound applications where each individual task spends most of its time waiting for IO. If the only thing your application does is run computations in parallel, you should be using rayon. That said, it is still possible to "mix & match" if you need to do both. See this blog post for a practical example

Tokio is for concurrency, not parallelism. Use it for IO stuff. They say rayon is good for that, but I haven't used that. If you just want something simple, I'd recommend working with threadpool.