SCHDOFLZ parameter

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Threshold for activating zIIP subtasks


Default value
Parameter type
Where set
On User 0's parameter line or reset by system manager.
Related products
M204 HPO
Model 204 V7.4


This parameter applies to z/OS only.

On a z/OS system, Model 204 zIIP support enables you to offload Model 204 work from regular processors to zIIP processors.

SCHDOFLZ specifies the target number of threads on the zIIP offload queue per active task. Setting this parameter makes the Model 204 zIIP subtask scheduler more responsive to instantaneous increases in load.

The default value, 2, means that if there are more than twice as many units of zIIP offloadable work waiting to be processed in a zIIP subtask as there are active subtasks, and fewer than AMPSUBZ subtasks are currently running, another zIIP offload subtask is activated.

SCHDOFLZ has no effect if either of these is true:

  • zIIP SRBs are not in effect in an Online (NMPSUBZ is 0).
  • The number of active SRBs (AMPSUBZ) is set to 0.

If AMPSUBZ is 1, a zIIP subtask is activated as soon as there is any offloadable work, and it then runs until there is no more offloadable work for it to process. So with AMPSUBZ set to 1, SCHDOFLZ does not affect any zIIP subtask activation decisions. However, under Model 204 7.5 and 7.6, it would affect non-SRB MP subtask activation and zIIP assistance decisions. Under Model 204 7.7 and later, this aspect of SCHDOFLZ is subsumed by SCHDOFLS.

SCHDOFL performs the same function as SCHDOFLZ for non-SRB MP subtasks. SCHDOFLS controls how aggressively MP subtasks are started to help out zIIP subtasks, as well as how aggressively MP subtasks take work from zIIP subtasks.

Prior to Model 204 7.7, the minimum allowed value for SCHDOFLZ is 1. Under Model 204 7.7 and later, it is 0, though it is probably a bad idea to set SCHDOFLZ to 0 unless the MPDELAYZ parameter is set to a non-zero value.