MPDELAYZ parameter
Delay before activating zIIP subtask
Summary
- Default value
- 0
- Parameter type
- System
- Where set
- On User 0's parameter line or reset by system manager.
- Related products
- All
- Introduced
- Model 204 V7.7
Description
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 value of 0 means that if the number of units of work queued to zIIP subtasks exceeds some limit as indicated by the SCHDOFLZ parameter, a zIIP subtask is immediately started. The benefit of setting MPDELAYZ to a non-zero value is that it prevents a large number of zIIP subtasks being started when a burst of units arrive (a common occurrence when dealing critical file resource conflicts) only to have most of them quickly deactivate because too many were started for the amount of work to be done. Activating and deactivating zIIP subtasks can have non-trivial CPU costs.
MPDELAYZ has no effect if either of these is true:
- MP/204 is not in effect in an Online (NMPSUBZ is 0).
- The number of active szIIP ubtasks (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, it might make sense to reduce SCHDOFLZ to 1 or maybe even 0 as both parameters attempt to solve the same problem (too much zIIP subtask activation/deactivation) and using both can reduce throughput or response times.
The MPDELAY parameter provides the same functionality as MPDELAYZ for MP (non-zIIP/SRB) subtasks.
An additional benefit of using MPDELAYZ is that by delaying starting zIIP subtasks, it will delay when a MP subtask might take work from the zIIP offload queue – MP subtasks will not process zIIP work unless all AMPSUBZ zIIP subtasks are active.