baa8ddb6___Compiling___Running_Programs__Description
[Environment Variable] AIXTHREAD_SCOPE=S or P (default=P) [Description] 
Sets the thread contention scope to be system (S) or process (P). When system contention scope is used, each user thread is directly mapped to one kernel thread. This is the appropriate setting for most scientific applications in which one wants the user threads to map one-to-one to processors. Process contention scope (P) is best when there are many more threads than processors. When process contention scope is used, user threads share a kernel thread with other (process contention scope) user threads in the process.
TAMU Supercomputing Facility -- Hydra User Guide: Compiling & Running Programs
Description