CODEWITHSUNDEEP
javajava-native-interface
gpuguy
gpuguy

Reputation: 4585

Measuring overhead of calling through JNI

To see if I can really take any benefit of native code (written C) by using JNI (instead of writing complete java application), I want to measure overhead of calling through JNI. What is the best way to measure this overhead?

Upvotes: 4

Views: 1130

Answers (3)

maaartinus
maaartinus

Reputation: 46422

Measuring the overhead alone may give you strange results. I'd code a small part of the performance-critical code in both Java and C++ and measure the program performance, e.g., using caliper (microbenchmarking is quite a complicated thing and hardly anybody gets it right).

I would not use any profiler, especially C++ profiler, since the performance of the C++ part alone doesn't matter and since profilers may distort the results.

Upvotes: 1

Stephen C
Stephen C

Reputation: 718798

I wouldn't use a profiler to do quantitative performance testing. Profiling tends to introduce distortions into the actual timing numbers.

I'd create a benchmark that performed one of the actual calculations that you are considering doing in C and compare the C + JNI + Java version against a pure Java version. Be sure that you are comparing apples and apples; i.e. profile and optimize both versions before you benchmark them.

To do the actual benchmarking, I'd construct a loop that performed the calculation a large number of times, record the timings over a large number of iterations and compare. Make sure that you take account of JVM warmup effects; e.g. class loading, JIT compilation and heap warmup.

Like Thihara, I doubt that using C + JNI will help much. And even if it does, you need to take account of the downsides of JNI; e.g. C code portability, platform specific build issues ... and possible JVM hard crashes if your native code has bugs.

Upvotes: 2

Thihara
Thihara

Reputation: 6969

Use a C++ profiler and a Java profiler. They are available in IDEs for Java. I can only assume in the case of C++ though. And whatever test you design please run through a substantial number of loops to minimize environmental errors.

Oh and do post the results back since I'm also curious to see if there are any improvement in using native code over modern JVMs. Chances are though you won't see a huge performance improvement in native code.

Upvotes: 0

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