In field, we have many cases where GC Locker is active. When thread is stalled by GC Locker, we have a nice message in gc+jni log:
 https://github.com/openjdk/jdk/blob/9b6f6c5c9dd6d0fbb056e8d84c3a0888a3320edf/src/hotspot/share/gc/shared/gcLocker.cpp#L112

However, we do not have any visibility into how fast a thread resumes from that stall. Nominally, one would assume the thread resumes when the next GC cycle clears the lock, but it might still take quite a bit of time. It would be useful for in-field diagnostics to also report when thread resumes from GC locker stall.

Probably jni_lock and jni_unlock would enjoy a more verbose logging as well.