Hi all I'm having an problem with my JNI library. The execution time of the same code changes from one phone to the other. I thought it was just because we were testing on an old phone but recently I run on htc legend and all the jni code was slow...
I run the profiler and its really a night and day difference: on some phone the jni functions take 15% to 20% as on the other phones it takes 40% and 50% for the same conditions...
anybody has an explanantion?
If one of the phones use JIT (Just In Time) Compiler added in Foryo (2.2) than that one should be much faster then your older ones. Are you testing it using the same android version?
Apart from that Some devices are better in float-point math than others. Devices which does not implement an FPU will emulutae float point operations. Here you can find a nice blog post about it: http://www.badlogicgames.com/wordpress/?p=71.
There are planty of sources on how to implement a float point system using fixed point arithmetics: http://en.wikipedia.org/wiki/Fixed-point_arithmetic
Processors are certainly not created equal; they have different feeds, speeds, caching and such. The obvious explanation is that is is the processor.
Additionally system-wide things may impact processing - if you are, say, processing an image taken by the camera using JNI, the size of the image may be device-specific.
Additionally you have to check you are measuring thread-time and wall-clock time; if look at timings relative to the parts of the code that are Java, you might be seeing a relative speed-up in the Java (e.g. JIT in Android 2.2) and not a slow-down in the JNI.