GLYPH<SM590000> On the z/OS side:  – CF signal is received by a shared-engine z/OS image (arrival of a List Notification  signal).  – An asynchronous CF operation completes. GLYPH<SM590000> Dedicated ICFs GLYPH<SM590000> Shared ICFs GLYPH<SM590000> Dedicated CPs GLYPH<SM590000> Shared CPs The interrupt causes the receiving partition to be dispatched by an LPAR, if it is not  dispatched. This process allows the request, signal, or request completion to be recognized  and processed in a more timely manner. After the image is dispatched, “poll for work” lo gic in CFCC and z/OS can be used largely as  is to locate and process the work. The new interrupt expedites the redispatching of the  partition. LPAR presents these Coupling Thin Interrupts to the guest partition; therefore, CFCC and  z/OS both require interrupt handler support that can deal with them. CFCC also changes to  relinquish control of the processor when all available pending work is exhausted, or when the  LPAR undispatches it off the shared processor, whichever comes first. A CF image can have one of the following combinations that are defined in the image profile: Shared ICFs add flexibility. However, running only with shared coupling facility PUs (ICFs or  CPs) is not a preferable production configuration. It is preferable for a production CF to  operate by using dedicated ICFs. With CFCC Level 19 (and later; z14 ZR1 servers run CFCC  level 22), Coupling Thin Interrupts are available, and dedicated engines continue to be  recommended to obtain the best coupling facility performance. The CPC on the left side of Figure 3-9 has two environments that are defined (production and  test), and each has one z/OS and one coupling facility image. The coupling facility images  share an ICF. CF processor combinations z/OS Prod z/OS Prod Setup HMC  Partition  Image Profile ICF CP CF  CF  Test Sysplex z/OS Test z/OS Test CF  Figure 3-9 ICF options: Shared ICFs  Chapter 3. Central processor complex system design  87