184 IBM eServer zSeries 900 Technical Guide
Figure 5-3 z900 ICF options - Shared ICFs
5.2.5 Dynamic CF dispatching and dynamic ICF expansion
The CF Control Code (CFCC), the CF Operating System, is implemented using the Active
Wait
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 CF LP. If this LP 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 CFCC: 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 z900 general processors 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 CF Images.
With Dynamic ICF Expansion, a CF Image using one or more
dedicated
ICFs can also use
one or more
shared
CPs of this same machine. The CF 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 processes.
Figure 5-4 shows a situation where the external CF goes down (for maintenance, for
example) and the allocated ICFs capacity on the left machine is not big enough to maintain
its own workload plus that of the external CF. With Dynamic ICF Expansion, the remaining CF
Image can be expanded over shared CPs from the z/OS image. This z/OS image
must
have
all CPs defined as
shared
and the Dynamic CF Dispatch function must be activated. Dynamic
ICF Expansion is available on z900 Model 100 and general purpose models that have at least
one ICF.
Dynamic ICF Expansion requires that Dynamic CF Dispatching be activated (DYNDISP ON).
z/OS
Prod
z/OS
Prod
Function Setup
HMC
z900
Partition
Image
Profile
ICF
CP
CF CF
Test Sysplex
z/OS
Test
z/OS
Test

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