Level 24 coupling facility

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A level 24 coupling facility (CFLEVEL=24) provides the following enhancements:
  • CFCC Fair Latch Manager
    • This is an enhancement to the internals of the Coupling Facility (CFCC) dispatcher to provide CF work management efficiency and processor scalability improvements, as well as improve the “fairness” of arbitration for internal CF resource latches across tasks.
  • CFCC Message Path Resiliency Enhancement
    • CF Message Paths use a z/OS-provided system identifier (SYID) to uniquely identify which z/OS system image, and instance of that system image, is sending requests over a message path to the CF.
    • When a z/OS system IPLs, message paths are supposed to be deactivated via system reset, and their SYIDs are supposed to be cleared in the process; During IPL, z/OS will then re-activate the message paths with a new SYID that represents the new instance of z/OS that is currently using the paths
    • On rare occasions, a message path may not get deactivated during system reset / IPL processing, leaving the message path left active with the z/OS image’s OLD, now-obsolete SYID. From the CF’s perspective, the incorrect SYID persists, and prevents delivery of signals to the z/OS image currently using that message path.
    • This new resiliency mechanism will transparently recover for this “missing” message path deactivate (if and when that ever happens)
  • CFCC Change Shared-Engine CF Default to DYNDISP=THIN
    • Make DYNDISP=THIN the default mode of operation for coupling facility images that use shared processors