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

[Stuart Douglas]

There is no guarantee that connections will be evenly distributed between
IO threads. Once a client has connected the connection is tied to that IO
thread, so it may be that you are just ending up with 2 connections on 4
threads.

Stuart




On Wed, Jul 25, 2018 at 10:02 AM R. Matt Barnett <barnett at rice.edu> wrote:

> 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
>
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