Controlling initiator dispatch priority in goal mode

When running in compatibility mode, initiators were assigned the dispatching priority that iss specified by the PVLDP keyword in the IEAIPSxx parmlib member. In goal mode, initiators run in service class SYSSTC with a fixed dispatching priority of 254 and there was no way to adjust or change the dispatching priority. The work running under the initiator is assigned its installation specified service class during SYSEVENT JOBSELCT processing. If there are cpu intensive exits that run prior to job select processing, the work will run at dispatching priority 254 and this can potentially impact high importance work.

A new parameter, INITIMP, in the IEAOPTxx member of SYS1.PARMLIB has been defined to allow an installation to set the initiator dispatching priority. The new dispatching priority applies to JES, APPC and OMVS initiators. Parameter INITIMP can be set as follows:

• INITIMP=0
  Is the same as if the parameter hasn't been defined. The initiator dispatching priority is set to 254.
   
• INITIMP=1,2, or 3
  Defines that the initiator dispatching priority has to be lower than the dispatching priority for CPU critical work with the same or a higher importance level.
  If no service class with the cpu critical attribute and a corresponding or higher importance level is defined in the WLM policy, the dispatching priority is calculated in the same way as for parameter INITIMP=E.
   
• INITIMP=E
  Defines that the initiator dispatching priority will be calculated in the same way as the enqueue promotion dispatching priority. The dispatching priority is calculated dynamically to ensure access to the processor. It should not impact high importance work, however there is no guarantee that CPU critical work will always have a higher dispatching priority.

The default is INITIMP=0. So if the INITIMP parameter is not defined or if it is defined as INITIMP=0, all JES, APPC and OMVS initiators will run at dispatching priority 254 as they currently do today, ensuring that the current system behavior remains unchanged. Therefore, no changes or updates to the OPT are necessary unless your installation requires the dynamic calculation of the initiator dispatching priority.

If your installation requires the dynamic calculation of the initiator dispatching priority, you will need to specify the new parameter INITIMP in the IEAOPTxx member of SYS1.PARMLIB When specifying an INITIMP value, it will only affect the system it has been set on. You can activate a new OPT parmlib member with the SET command: SET OPT=xx.

After specifying an INITIMP value,the initiator will still show a service class of SYSSTC but the dispatching priority will be based on the INITIMP setting.

Note that you should also install OA03581 so that idle initiators will always run at dispatching priority x'FE' if INITIMP is set to 0 or is not specified in the IEAOPTxx member of SYS1.PARMLIB.