You have several options if you want to fine-tune performance of the z/OS shell. You can use the _BPX_SHAREAS and _BPX_SPAWN_SCRIPT . Other helpful hints include controlling the use of STEPLIBs and ensuring that the sticky bit is on.

Guideline: Do not specify PRIORITYPG and PRIORITYGOAL in BPXPRMxx unless you need nice() and setpriority() support. It is simplest and best to give MVS™ full control over priorities of work.