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Re: [jetty-dev] Trying to make sense of slow server response times
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Hi,
first of allL good problem description and summary.
Could you add some details on CPU architecture and other hardware differences on the machines you‘ve used?
I‘d first try to find some patterns about the CPU architecture (number of cores, cpu L1/L2/L3 cache sizes, memory bandwith between main memory etc.). Did you also monitor and compare context switches, etc.?
Finding the root cause of such problems is usually hard.
Cheers,
Thomas
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!
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