This is really important. I think author found results surprising and unintuitive, because they've been looking at the wrong thing. Rust libraries are designed

This is really important. I think author found results surprising and unintuitive, because they've been looking at the wrong thing. Rust libraries are designed to be fast when optimized with LLVM. Rust has a lot of layers of abstractions, and they're zero cost only when everything is fully optimized. If you look at unoptimized miri execution, or insert code-level instrumentation that gets in the way of the optimizer, these aren't zero cost any more, and overheads add up where they normally don't exist.