very low TCP performance

I would expect performance when reading/writing from/to TCP to be in the GB/s. I wrote a small program to test the bandwidth:
https://git.rwth-aachen.de/niklas.eiling/rust-network-benchmark
Running it without rusty-hermit (i.e., using a local loopback socket) yields approx. 5 GiB/s bandwidth.
When running it in rusty-hermit I only get the following bandwidths:
Write BW: 0.039 MiB/s
Read BW: 0.53 MiB/s

My program is very similar to this benchmark in the rusty-hermit repo:
https://github.com/hermitcore/rusty-hermit/tree/master/benches/netbench
This also shows very bad performance.