With a similar change to RawNetty, it's about 10x faster than Fs2IO, and still 5x faster than Fs2Netty with this PR.

Using availableProcessors for workers in RawNetty, epoll if available:
RawNetty: 1520858 request/sec, 1520858 response/sec

(epoll didn't make much of a difference for this test, NIO gets about the same results)

I did a bunch of additional benchmarks with more recent versions of fs2 and cats-effect. Seems like there's a significant performance hit related to tracing in cats-effect, and possibly a smaller one in fs2. There's a decent amount of variance, so the first might not really be much slower than the second, but anyways... for future reference:

3.0.6 (tracing disabled, CE 3.3.3) Speed: 320236 request/sec, 320236 response/sec
3.2.4 (tracing disabled, CE 3.3.3) Speed: 264885 request/sec, 264885 response/sec
3.2-10-421c242 (main, tracing enabled, CE 3.3.3) Speed: 196105 request/sec, 196105 response/sec
3.2-10-421c242 (main, tracing disabled, CE 3.3.3) Speed: 285688 request/sec, 285688 response/sec
3.2-10-421c242 (main) Speed: 163657 request/sec, 163657 response/sec
3.2.4 Speed: 179674 request/sec, 179674 response/sec
3.2.3 Speed: 168397 request/sec, 168397 response/sec
3.2.2 Speed: 240868 request/sec, 240868 response/sec
3.2.1 Speed: 209951 request/sec, 209951 response/sec
3.1.6 Speed: 215442 request/sec, 215442 response/sec
3.1.0 Speed: 234656 request/sec, 234656 response/sec
3.0.6 Speed: 273681 request/sec, 273681 response/sec

@djspiewak Not sure if you missed this, or if it's just not interesting? I'll close the PR in January, I'm getting tired of seeing it open in my PR list. ;)

Especially with the io_uring and epoll stuff being worked on in CE3, maybe this fs2-netty isn't all that relevant anymore.