Level 25 coupling facility

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A level 25 coupling facility (CFLEVEL=25) provides the following enhancements:
  • CFCC change to dynamic dispatching
    • DYNDISP=THIN is the only option.
  • Cache residency time metrics for directory/data entries
    • Allows cache effectiveness monitoring by the exploiter
    • Allows monitoring of effects of cache-unfriendly batch processes (for example, image copy, reorg, update-intensive workloads).
    • The metrics show how long data entries or directory entries remain resident in the cache structure from the time they are created until the time they are eventually reclaimed out of existence
    • Moving weighted average directory entry and data area residency times, in microseconds, are provided
    • Reclaims from all causes are included in the averaging: Creation of new directory entries or data areas, ECR contractions or reapportionments, etc.
    • Residency times are accounted for only at time of reclaim (not while the cache objects still remain in use)
    • Explicit deletions of these objects also do not factor into the metrics.
  • Cache retry buffer support for IFCC retry idempotency
  • Lock record data reserved entries for structure full recovery
  • CF performance and scalability improvements through CF dispatcher changes.
  • CF Cache and Lock structure resiliency improvements
    • CFLEVEL 25 support provides improved resiliency support for CF cache and lock structure usage. The CF now implements a functional retry buffer capability that applies to the subset of CF cache and lock commands that are not perfectly retriable when an Interface Control Check (IFCC) or other link-related error interrupts the normal request flow to or from the CF image. Retry buffers make it possible for z/OS to always determine the outcome of such CF operations following a transient link error, avoiding any ambiguities related to the CF structure updates made by those requests. z/OS makes use of CF retry buffers to improve the resiliency of these CF structure operations without requiring any software updates by the end-user function that is exploiting the CF structure for its data sharing purposes.
    • Additionally, CFLEVEL 25 provides lock structure exploiters with the new capability to dedicate a subset of lock structure record data entries which are to be reserved for recovery use only. Exploiters may reserve these record data entries and thereby ensure that even when all of the normal record data entries in a lock structure have been used up, the special pool of dedicated recovery use entries still remains available for use in recovering from this structure-full condition.
  • Coupling link short-reach protocol efficiency improvements
    • Short-distance ICA SR coupling link protocols have been re-designed to provide reduced latency and improved CF service times for CF requests using these links. The improved CF service times for CF requests can translate into better Parallel Sysplex coupling efficiency and therefore reduced software costs for the attached z/OS images in the Parallel Sysplex, as synchronous CF requests directly consume z/OS-image processor resources as they are executed.
  • CF image scalability improvements
    • Coupling facility images are designed to provide improved CF image scalability compared to CF images on previous systems. The CF work manager has been re-designed to partition the available CF processors into small affinity groups of processors, and then affinitize CF tasks and all task-related control blocks and data areas to a specific processor affinity group. Furthermore, incoming work received on coupling links and the link buffers associated with them are also affinitized to a specific processor affinity group. This tight relationship between incoming work, executing work, and CF processor affinity groups minimizes the costs of processor cache disruption and movement of CF commands from processor to processor within the CF image as the CF workload is executing, providing improved CF processor scalability for CF images.