[jetty-dev] Trying to make sense of slow server response times

[easbar.mail@xxxxxxxxxx]

Dear Jetty Devs and Community,

hopefully I've come to the right place to ask for help with the 
following issue. I am puzzled by the server response times I am
measuring using a Jetty instance. I reduced the issue such that now 
there are only two HttpServlets. One just returns a constant number and 
serves as a baseline. The other calculates and returns the sum of all 
integers in an array. I also measure the time the actual summation takes.

On some machines everything seems fine: The response time of the servlet
that does the summation is roughly equal to the time the summation is 
expected to take. Querying the server only adds a minimal overhead.

But on others there is significant overhead (the servlet response is 
much slower than the actual summation), and on some the overhead is even 
proportional to the size of the array!

You can find the benchmark, instructions how to run it and a more 
detailed explanation of my results (in README.md) here: 
https://github.com/easbar/jetty_jmh_benchmark/commit/f32ca12256021c69589a90f460097887ac802740. 
I am referencing to this specific commit to avoid confusion in case 
there will be changes to the benchmark later.

I have tried using profilers and JVM flags like `-XX:+PrintCompilation` 
to find out what causes this slow down, but the server response times I 
am measuring still remain a complete mystery to me. They are very 
reproducible, i.e. whenever I run the benchmark I pretty much get the 
same result, but (qualitatively) different results for different 
machines. I also tried different JDK versions (8,11,17), and Jetty 9&11, 
but that does not seem to change anything.

Frankly speaking I don't really know what else to try to get to the 
bottom of this, which is why I came here.

Any kind of help would be highly appreciated, e.g.

* running the benchmark and posting your results
* looking at the results in README.md and giving some advice what I 
could do to debug this, or thinking about what *could* be the cause for 
such behavior

Thanks in advance!