Note that you’re changing multiple variables, namely the entire compiler and runtime.

If you know a system that both has async/await _and_ full-blown green threads, then I can try to test it.

Racket has full-blown green threads (virtual threads)[1] that serve as an alternative to the async/await paradigm. It also supports use of native (OS) threads[2].

[1] https://docs.racket-lang.org/reference/eval-model.html#%28pa...

[2] https://docs.racket-lang.org/reference/places.html

[&] https://docs.racket-lang.org/reference/futures.html

C++ has now both async (built-in) and multiple flavors of stackful coroutines (as external libraries). You can run both on top of ASIO so that you can measure purely difference of the coroutine implementation as opposed to the runtime.