Tokio (stackless coroutines) vs. May (stackful coroutines) in Rust

After investigating may_minihttp[0], which appears, for now, to be the fastest web framework on TechEmpower benchmarks[1], I saw the data below.

[0]: https://github.com/Xudong-Huang/may_minihttp [1]: https://www.techempower.com/benchmarks/#section=data-r23

==

tokio echo server

run the server by default with 2 threads in another terminal

    $ cd tokio-core
    $ cargo run --example=echo-threads --release
    $ target/release/examples/echo_client -t 2 -c 100 -l 100 -a 127.0.0.1:8080
    ==================Benchmarking: 127.0.0.1:8080==================
    100 clients, running 100 bytes, 10 sec.

    Speed: 315698 request/sec,  315698 response/sec, 30829 kb/sec
    Requests: 3156989
    Responses: 3156989
    target/release/examples/echo_client -t 2 -c 100 -l 100 -a 127.0.0.1:8080  1.89s user 13.46s system 152% cpu 10.035 total

run the server by default with 2 threads in another terminal

    $ cd may
    $ cargo run --example=echo --release -- -p 8000 -t 2
    $ target/release/examples/echo_client -t 2 -c 100 -l 100 -a 127.0.0.1:8000

    ==================Benchmarking: 127.0.0.1:8000==================
    100 clients, running 100 bytes, 10 sec.

    Speed: 419094 request/sec,  419094 response/sec, 40927 kb/sec
    Requests: 4190944
    Responses: 4190944
    target/release/examples/echo_client -t 2 -c 100 -l 100 -a 127.0.0.1:8000  2.60s user 16.96s system 195% cpu 10.029 total