Description

I'm trying benchmark_udp on an nrf52840dk over usbus_cdc_ecm.
I'm seeing some reliability issues with high load.

With down to -i 30, everything is fine.
From -i 29, the shell becomes unresponsive, but the node still pings and I can run more benchmark_udp (restart host tool).
From -i 14, the node seems to freeze. Fixed with #16831.

Steps to reproduce the issue

compile tests/usbus_cdc_ecm with benchmark_udp:

BOARD=nrf52840dk USEMODULE="benchmark_udp" make -Ctests/usbus_cdc_ecm clean all flash -j8

in riots shell:

bench_start <host-link-local-addr> 12345,

then on host:

./benchmark_server -i 14 :: 12345

Expected results

Shell and node stay responsive.

Actual results

Shell freeze or (seemingly) full node freeze.

Versions

Compiled on arch with gcc version 11.2.0.