> Also, it strikes me that ia64 has tons of different versions of > cmpxchg, and the one you use by default is the one with "acquire" > semantics
Not "tons", just two. You can ask for "acquire" or "release" semantics, there is no relaxed option. Worse still - early processor implementations actually just ignored the acquire/release and did a full fence all the time. Unfortunately this meant a lot of badly written code that used .acq when they really wanted .rel became legacy out in the wild - so when we made a cpu that strictly did the .acq or .rel ... all that code started breaking - so we had to back-pedal and keep the "legacy" behavior of a full fence :-( -Tony
