[POSSIBLE BUG] sendmsg ops returning -ETIME

[Victor Stewart <v@nametag.social>]

i wrote a quic performance tool to research maximal quic server
performance namely syscalls vs io-uring and quic library vs library
(in an apples to apples scenario).

i'm having some issues with the stability of the io-uring networking
layer... and at least thought my rings were just overflowing, but they
aren't. during most runs, all of a sudden submitted sendmsg ops start
failing and returning -ETIME... even though there are absolutely no
timeouts associated with those operations. and it's always that -ETIME
error delivered once things start to fail.

the only performance test implemented so far is a 1GB transfer over
udp over ipv6 loopback. my working guess at the moment is that the
operation pressure rate is exposing some kind of bug somewhere in
io-ring?

i just posted the project on github. the README is basic but i think
provides enough instructions to run the binaries and see for yourself.

let me know what data i can extract so we can quickly rule this
definitely my bug or definitely an io-uring bug. it's really the
bizzare -ETIME that makes me think it might not be mine.

the code is super brief, check perf.networking.cpp

https://github.com/victorstewart/quicperf