MPDELAYZ parameter

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Delay before activating zIIP subtask


Default value
Parameter type
Where set
On User 0's parameter line or reset by system manager.
Related products
Model 204 V7.7


This parameter specifies the number of milliseconds to delay starting additional zIIP/SRB subtasks when an extra one should be started based on SCHDOFLZ.

The default MPDELAYZ value of 0 means that if the number of units of work queued to zIIP subtasks exceeds the limit indicated by the SCHDOFLZ parameter, a zIIP subtask is immediately started. The benefit of setting MPDELAYZ to a non-zero value is seen when a burst of work units arrive: it prevents the immediate starting of a large number of zIIP subtasks only to have most of them quickly deactivate because too many were started for the amount of work to be done. Such demand bursts are a common occurrence when dealing with critical file resource conflicts, and activating and deactivating zIIP subtasks can have non-trivial CPU costs.

Usage notes

  • MPDELAYZ 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 zIIP subtasks (AMPSUBZ) is set to 0 or 1. (If AMPSUBZ is 1, a zIIP subtask is activated as soon as there is any zIIP runnable work, and it then runs until there is no more zIIP capable work for it to process.)
  • If MPDELAYZ is set, consider reducing SCHDOFLZ to 1 or 0, since both parameters attempt to solve the same problem (too much zIIP subtask activation/deactivation). Using both parameters can reduce throughput or response times.
  • An additional benefit of using MPDELAYZ is that delaying the starting of zIIP subtasks delays an MP subtask's taking of work from the zIIP offload queue — MP subtasks do not process zIIP work unless all AMPSUBZ zIIP subtasks are active.

See also

The MPDELAY parameter provides the same functionality as MPDELAYZ for MP (non-zIIP/SRB) subtasks.