IBM eServer zSeries 990 Technical Guide

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

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 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

processes.

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.

z/OSz/OS

Function

Setup

HMC

z990

Partition

Image

Profile

CF

IC F

CP

B

A

C

K

U

P

C

F

z/OSz/OS

CF

A

C

T

I

V

E

C

F

With Dynamic CF dispacting enabled, backup

CF becomes active only for new work

DYNDISP ON (CFCC cmd)

IMAGE Profile setup