On 26/06/2021 11:59 am, Andrew Rowley wrote:
On 25/06/2021 8:58 pm, Scott Chapman wrote:
If other platforms don't JIT as quickly or aggressively, or if their
JIT compiler isn't as smart as IBM's then their results may not be
the same. Similarly, if the IBM C compiler isn't as optimized as it
is on other platforms, it might underperform.
I don't know how long it takes for JIT to optimize the loop, 5 seconds
is a lot of passes and in CPU terms is a very long time so it's not
surprising that it is pretty good. The original Java code ran for 10
seconds. I reduced it to 5 to match the C++ implementation. I was
expecting a performance reduction due to warm up time but it wasn't
noticeable. The timing starts after the Java code is running so JVM
startup is not measured.
I think the C++ compiler/library is a large part of it. On other
platforms vector<bool> was apparently a big performance improvement,
on z/OS removing it was a big improvement. So if there is something
smart happening there on other platforms, there might be something not
so smart on z/OS. xlclang++ might recover that performance.
I think the C++ code is sub-optimal. The PrimesC code is 5x faster than
Java so if I were to compile that code with the C++ compiler would it
qualify as C++?
FWIW, I'm happy that Java stacks up so well on z/OS as I'm pretty much
coding 90% on the JVM these days. IBM have done a brilliant job
optimizing. But these bench tests are more about comparing
implementations of algorithms then equivalent implementations in
different programming languages.
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