Consider this benchmark:

https://github.com/openjdk/jdk/compare/master...mcimadamore:jdk:xor_bench?expand=1

Here, we compare the performance of code that copies arrays into off-heap storage ahead of a native call. It turns out that doing the copy using Unsafe::arrayCopy is 15-20% slower than using JNI's GetByteArrayRegion function.

Profiling the benchmark with perfasm reveals that Unsafe::arrayCopy boils down to:

StubRoutines::jlong_disjoint_arraycopy

Whereas for JNI we end up with this:

__memmove_avx_unaligned_erms

The latter, judging from the name, likely enjoys AVX optimizations, which seems the most likely explanation for the difference in the performance profile of the two code paths.