I thought Greg Dyck's post perfectly answered the what's and why's, including the sole reason for which the instruction was created.
Disablement for external and I/O interrupts prevents the work unit from being undispatched in between the serialized operation and the store that sets the footprint. CSST accomplishes that by combining the two into one instruction. Not having to disable is of course simpler and also makes this function available to problem state programs (since they cannot disable). One might ask "if you were disabled for external and I/O interrupts, could LPAR undispatch you from the processor in between the serialized operation and the store?". The answer must be "yes", but this would not be visible to the work unit. As far as z/OS was concerned, the work unit would still be dispatched. Peter Relson z/OS Core Technology Design ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
