IBM eServer zSeries 900 Technical Guide

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