Assigning z/OS dispatching priorities

Choose a coordinated dispatching priority scheme for the total system. The scheme must reflect the relative worth of any subsystems that are to execute concurrently.

The IMS control region operates in protect key 7 as a system task. This reduces the number of executable instructions for some supervisory functions.

Job dispatching priority

The job dispatching priority dictates the sequence jobs are given to available machine cycles. Any job with a dispatching priority higher than the control region causes interference. Although VTAM® or TCAM normally runs at high priority (as do JES and the z/OS® Master Scheduler), you should review the position of other work (principally TSO and batch) in relation to the IMS control region and the dependent regions.

Dependent region dispatching priority

It is important that both the control region and the dependent regions obtain priority processing. The parallel DL/I function in IMS enables most of the DL/I call processing to be performed in the dependent regions. If the assigned dispatching priority is too low, the promptness of service to application programs declines. Usually, you set the BMP region priority lower than MPP priorities. The BMP priorities should, however, immediately follow the MPPs, because they contend for the same control region resources, such as program isolation enqueues. Normally, TSO first period work is placed below the IMS control region; it might be above the dependent regions. TSO second period work and batch are normally placed below the IMS dependent regions.

Setting a performance group number under z/OS

You can assign a unique performance group number to each IMS region. In this way, you can obtain Resource Measurement Facility (RMF) report statistics separately for each region.

If the DL/I separate address space option is used, you might decide to include both the control and DL/I separate address spaces in the same RMF performance group.

Setting priorities in a DBCTL environment

For a DBCTL environment, the CCTL region should have a higher priority than the DBCTL region, which should have a higher priority than any batch processing regions.

CICS® might run at a higher priority than the DBCTL region. Adjust the priorities of the DBCTL and CICS regions depending on the workload and resources available to your system.

Dispatching priorities

Dispatching priorities are set by the z/OS Workload Manager (WLM) and are based in part on the relative importance you assign in the WLM ISPF panels to each IMS address space.

Related reading: For more information on assigning WLM importance, see Workload Manager and IMS.

The following figure shows an example WLM ISPF display of the relative dispatching priorities assigned to all address spaces known to WLM. The dispatching priority of each address space appears as a hexadecimal value in column DP, with X'FF' being the highest priority. Address spaces with a lower value have a lower priority.

Figure 1. Relative dispatching priority (column DP) displayed in the WLM ISPF panel

 NP   JOBNAME  StepName ProcStep JobID    Owner    C Pos DP Real Paging 00000100
      ALLOCAS  ALLOCAS                               NS  FF  806   0.00 00000110
      IOSAS    IOSAS    IEFPROC                      NS  FF  256   0.00 00000120
      IXGLOGR  IXGLOGR  IEFPROC                      NS  FD  803   0.00 00000130
      SMS      SMS      IEFPROC                      NS  FE  329   0.00 00000140
      SMF      SMF      IEFPROC                      NS  FF  363   0.00 00000150
      JES2AUX  JES2AUX                               NS  F9  120   0.00 00000160
      IRL2194  IRL2194  IRLM     STC00312 ++++++++   NS  FD  283   0.00 00000170
      NETMONC4 NETMONC4 SYSTEM   STC00005 ++++++++   NS  FB  240   0.00 00000180
      JES2     JES2     IEFPROC                      NS  F9 3095   0.00 00000190
      VTAM94   VTAM94   IEFPROC  STC00002 ++++++++   NS  FD 2492   0.00 00000191
      SOFIMSP  SOFIMSP           STC00006 ++++++++   LO  FF  226   0.00 00000192
      MPC4A04  REGION            JOB00323 USRT008  A NS  F3  385   0.00 00000200
      MPC4A05  REGION            JOB00324 USRT008  A NS  F3  385   0.00 00000300
      MPC4A06  REGION            JOB00325 USRT008  A NS  F3  385   0.00 00000400
      MPC4A07  REGION            JOB00326 USRT008  A NS  F3  385   0.00 00000500
      MPC4A08  REGION            JOB00327 USRT008  A NS  F3  385   0.00 00000600
      SCIC94   SCIC94   IEFPROC  STC00313 ++++++++   NS  FD  460   0.00 00000700
      OMC94    OMC94    IEFPROC  STC00314 ++++++++   NS  FD  442   0.00 00000800
      CQSC94   CQSC94   IEFPROC  STC00315 ++++++++   NS  F7 1052   0.00 00000900
      RMC94    RMC94    IEFPROC  STC00316 ++++++++   NS  FD  507   0.00 00001000
      I91CTLC4 I91CTLC4 IEFPROC  STC00317 ++++++++   NS  F7  12T   0.00 00001100
      I91DLSC4 I91DLSC4 IEFPROC  STC00318 ++++++++   NS  F5  27T   0.00 00001200
      I91DBRC4 I91DBRC4 IEFPROC  STC00319 ++++++++   NS  FD  617   0.00 00001300
      BPXOINIT BPXOINIT BPXOINIT                     IN  FF  162   0.00 00001400
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