Rust doesn't use M:N threading (coroutines) because it was found to be slower than 1:1 threading in practice. Async/await avoids allocation of stacks entirely a

Rust doesn't use M:N threading (coroutines) because it was found to be slower than 1:1 threading in practice. Async/await avoids allocation of stacks entirely and can therefore be faster than both 1:1 threading and M:N threading.