On 23/03/2023 3:42 am, René Jansen wrote:
Does anybody know how to ask the J9 (Java 8) on z/OS how to show me what it
does when the JIT decides native code would be best?
I think it is difficult to pin down the native code because the JIT is
not a one-time, fixed output compiler.
Java can monitor the execution of code and come back and perform further
optimization on hot areas of code. The docs even talk about "optimistic
optimization" where certain assumptions are made and the code can later
be de-optimized if they turn out to be false. So trying to look at
specific machine code seems like a problem.
What types does the code use? I don't see a built in decimal type other
than BigDecimal, so the opportunity for Java to use DFP instructions
seems limited - but I don't really know.
My inclination would be to try to get some performance figures for the
Java code using e.g. JMH (which provides warmups etc. to trigger JIT
optimizations) and try to build the equivalent the other language.
Benchmarks have their pitfalls, but it's probably still better than
trying to compare the native code.
--
Andrew Rowley
Black Hill Software
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