It's fast, but it depends on exactly what you're doing. There is always a bit of work managing the stack and converting between ABIs, and JNI is quite poor in p

It's fast, but it depends on exactly what you're doing. There is always a bit of work managing the stack and converting between ABIs, and JNI is quite poor in performance when dealing with anything other than primitive types. The sort of thing Panama is adding is support for layouts of structures so that you can get results to and from C quickly, along with things like expressing vector algorithms in a way that allows good optimisation on different CPUs.