MPDELAYZ parameter: Difference between revisions
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The default <var>MPDELAYZ</var> value of 0 means that if the number of units of work queued to zIIP subtasks exceeds the limit indicated by the <var>SCHDOFLZ</var> parameter, a zIIP subtask is immediately started. The benefit of setting <var>MPDELAYZ</var> 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.</p> | The default <var>MPDELAYZ</var> value of 0 means that if the number of units of work queued to zIIP subtasks exceeds the limit indicated by the <var>SCHDOFLZ</var> parameter, a zIIP subtask is immediately started. The benefit of setting <var>MPDELAYZ</var> 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.</p> | ||
< | |||
<var>MPDELAYZ</var> has no effect if either of these is true: | ==Usage notes== | ||
<ul> | |||
<li><var>MPDELAYZ</var> has no effect if either of these is true: | |||
<ul> | <ul> | ||
<li>MP/204 is not in effect in an Online (<var>NMPSUBZ</var> is 0).</li> | <li>MP/204 is not in effect in an Online (<var>NMPSUBZ</var> is 0).</li> | ||
<li>The number of active szIIP ubtasks (<var>AMPSUBZ</var>) is set to 0 or 1. (If <var>AMPSUBZ</var> 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.)</li> | <li>The number of active szIIP ubtasks (<var>AMPSUBZ</var>) is set to 0 or 1. (If <var>AMPSUBZ</var> 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.)</li> | ||
</ul> | </ul></li> | ||
< | |||
If <var>MPDELAYZ</var> is set, consider reducing <var>SCHDOFLZ</var> 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.</ | <li>If <var>MPDELAYZ</var> is set, consider reducing <var>SCHDOFLZ</var> 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.</li> | ||
<li>An additional benefit of using <var>MPDELAYZ</var> 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 <var>AMPSUBZ</var> zIIP subtasks are active. | |||
</li></ul> | |||
==See also== | |||
<p> | <p> | ||
The <var>[[MPDELAY parameter|MPDELAY]]</var> parameter provides the same functionality as <var>MPDELAYZ</var> for MP (non-zIIP/SRB) subtasks. | The <var>[[MPDELAY parameter|MPDELAY]]</var> parameter provides the same functionality as <var>MPDELAYZ</var> for MP (non-zIIP/SRB) subtasks. | ||
</p> | </p> | ||
[[Category:System parameters]] | [[Category:System parameters]] | ||
[[Category:Parameters]] | [[Category:Parameters]] | ||
Revision as of 21:04, 2 August 2016
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 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:
- 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, 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.