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