168 IBM ^ zSeries 990 Technical Guide
7.2.7 Dynamic CF dispatching and dynamic ICF expansion
The CF Control Code (CFCC), the “CF Operating System,” is implemented using the Active
technique. This means it is always running (processing or searching for service) and
never enters into a wait state. This also means that it gets all the processor capacity (cycles)
available for the Coupling Facility logical partition. If this logical partition uses only dedicated
processors (CPs or ICFs), this is not a problem. But this may not be desirable when it uses
shared processors (CPs or ICFs).
Dynamic CF dispatching provides the following function on a Coupling Facility: If there is no
work to do, it enters into a wait state (by time). After an elapsed time, it wakes up to see if
there is any new work to do (requests in the CF Receiver buffer). If there is no work, it will
sleep again for a longer period of time. If there is new work, it enters into the normal Active
Wait until there is no more work, starting the process all over again. This saves processor
cycles and is an excellent option to be used by a production backup CF or a testing
environment CF. This function is activated by the CFCC command DYNDISP ON.
The z990 CPs can run z/OS and/or OS/390 operating system images and CF Images. For
software charge reasons, it is better to use ICF processors to run Coupling Facility images.
Figure 7-5 z990 Dynamic CF Dispatching (shared CPs or shared ICF PUs)
With Dynamic ICF Expansion, a Coupling Facility image using one or more dedicated ICFs
can also use one or more
shared CPs of this same server. The Coupling Facility image uses
the shared CPs only when needed, that is, when its workload requires more capacity than its
dedicated ICFs have. This may be necessary during peak periods or during recovery
Figure 7-6 on page 169 shows an example where the server on the left has a production and
a test Coupling Facility that has dedicated and shared ICF PUs. This configuration enables
the Coupling Facilities to utilize the shared ICF PUs when workload becomes excessive.
Additionally, if the alternate production Coupling Facility goes down (for maintenance, for
example) and the allocated ICFs’ capacity on the left server is not big enough to maintain its
own workload plus that of the other Coupling Facility, then with Dynamic ICF Expansion, the
remaining Coupling Facility image can be expanded over shared ICF PUs.
With Dynamic CF dispacting enabled, backup
CF becomes active only for new work
DYNDISP ON (CFCC cmd)
IMAGE Profile setup