7.5% speed gain from BEAMJIT. 2.8x faster file ops because of dirty nifs support. Multiple poll sets. This is good stuff, I can't wait to benchmark it and play with it!
Yes. The problem earlier was that NIFs had a maximum runtime of 1 millisecond before they needed to store their work and return control to BEAM, to avoid blocking the BEAM schedulers. Dirty NIFs refer to NIFs that can run for longer, on special dirty schedulers, without affecting the stability of the BEAM system.
[0] http://erlang.org/doc/tutorial/nif.html