Why huge performance gap between opencv c++ native and java code on Android?

edit

the code snippet as following: 1. java code

           try {
                Mat rgba  = Imgcodecs.imread(_path);
                Mat rgba_clone = rgba.clone();
                long  start = System.currentTimeMillis();
                Imgproc.GaussianBlur(rgba_clone, rgba_clone, new Size(3, 3), 9);
                long elapsedTimeMillis = System.currentTimeMillis()-start;
                Log.d(TAG, "java GaussianBlur costs " + elapsedTimeMillis + " ms.");
                rgba_clone.release();

                long rgba_addr = rgba.getNativeObjAddr();
                perfGaussBlur(rgba_addr);
                rgba.release();
            } catch (Exception e) {
                e.printStackTrace();
            }

native code:

cv::setUseOptimized(true);
cv::Mat&  rgba_ = (cv::Mat)rgba;
cv::Mat   rgba_clone = rgba_.clone();
LOGD("image size -> w: %d, h: %d", rgba_.cols, rgba_.rows);
int n_iter = 3;
timekeeper tm;
std::chrono::milliseconds duration;
for (int i = 0; i < n_iter; i ++)
    cv::GaussianBlur(rgba_clone, rgba_clone, cv::Size(9, 9), 3);
tm.timespan2now(duration);
LOGD("GaussianBlur cost: %ld ms.", (long)duration.count() / n_iter);

your java code measures "wall time", while the c++ code uses something based on cpu clock, so you compare apples to pears.

use cv::getTickCount() in both java/c++ code, and report back, please.

Thanks. I will try it.