bglockless
Update: in MPICH-3.1.1 we finally scrapped bglockless, (see this writeup on 3.1.1 and Blue Gene enhancements) but it’s still part of the system software on any BG /L BG /P or BG /Q machines. The following writeup is perhaps of historical interest, but it will be a while (maybe never) before mpich-3.1.1 is the default …