I'm the person who is running the rav1d bounty, also involved with the Rustls project. In many (most?) situations I think Rust is effectively as fast as C, but

I'm the person who is running the rav1d bounty, also involved with the Rustls project. In many (most?) situations I think Rust is effectively as fast as C, but it's not a given. They're close enough that depending on the situation, one can be faster than the other. If you told me I had to make a larger and more complex piece of code fast though, I'd pick Rust. Because of the rules that the Rust compiler enforces, it's easier to have confidence in the correctness of your code and that really frees you up when you're dealing with multi-threaded or algorithmic complexity. For example, you can be more confident about how little locking you can get away with, what the minimum amount of time is that you need to keep some memory around, or what exact state is possible and thus needs to be handled at any given time. There are some things that make rav1d performance particularly challenging. For example - unlike Rustls, which was written from the start in Rust, rav1d is largely the result of C to Rust translation. This means the code is mostly not idiomatic Rust, and the Rust compiler is generally more optimized for idiomatic Rust. How much this particular issue contributes to the performance gap I don't know, but it's a suspect and to the extent that it's worth pursuing, one would probably want to figure out where being idiomatic matters most instead of blanket rewriting everything.