[undertow-dev] Unable to concurrently use all available IO Threads under load on Red Hat

Hello, I'm experiencing an Undertow performance issue I fail to understand.  I am able to reproduce the issue with the code linked bellow. The problem is that on Red Hat (and not Windows) I'm unable to concurrently process more than 4 overlapping requests even with 8 configured IO Threads.   For example, if I run the following program (1 file, 55 lines): https://gist.github.com/rmbarnett-rice/668db6b4e9f8f8da7093a3659b6ae2b5 ... on Red Hat and then send requests to the server using Apache Benchmark...     > ab -n 1000 -c 8 localhost:8080/ I see the following output from the Undertow process:     Server started on port 8080     1     2     3     4 I believe this demonstrates that only 4 requests are ever processed in parallel.  I would expect 8.  In fact, when I run the same experiment on Windows I see the expected output of     Server started on port 8080     1     2     3     4     5     6     7     8 Any thoughts as to what might explain this behavior? Best, Matt