See https://klausi.github.io/rustnish/2018/08/31/benchmarking-a-rust-web-application.html
This is probably the same underlying issue that was discussed in Getting tokio to match actix-web performance - #10 by fpgaminer
Interesting! I found that actix-web performs much worse for me. What I'm seeing is that Hyper/Tokio seems to have performance problems with multithreading compared to Varnish.