MPDELAY parameter: Difference between revisions
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This parameter specifies the number of milliseconds to delay starting additional MP subtasks when an extra one should be started based on <var>[[SCHDOFL parameter|SCHDOFL]]</var>.</p> | This parameter specifies the number of milliseconds to delay starting additional MP subtasks when an extra one should be started based on <var>[[SCHDOFL parameter|SCHDOFL]]</var>.</p> | ||
<p> | <p> | ||
The default value of 0 means that if the number of units of work queued to MP subtasks exceeds some limit as indicated by the <var>SCHDOFL</var> parameter, an MP subtask is immediately started. The benefit of setting <var>MPDELAY</var> to a non-zero value is | The default value of 0 means that if the number of units of work queued to MP subtasks exceeds some limit as indicated by the <var>SCHDOFL</var> parameter, an MP subtask is immediately started. The benefit of setting <var>MPDELAY</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 MP 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 MP subtasks can have non-trivial CPU costs.</p> | ||
< | ==Usage notes== | ||
<var>MPDELAY</var> has no effect if either of these is true: | <ul> | ||
<li><var>MPDELAY</var> has no effect if either of these is true: | |||
<ul> | <ul> | ||
<li>MP/204 is not in effect in an Online (<var>NMPSUBS</var> is 0).</li> | <li>MP/204 is not in effect in an Online (<var>NMPSUBS</var> is 0).</li> | ||
<li>The number of active subtasks (<var>AMPSUBS</var>) is set to 0 or 1. (If <var>AMPSUBS</var> is 1, an MP 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.)</li> | <li>The number of active subtasks (<var>AMPSUBS</var>) is set to 0 or 1. (If <var>AMPSUBS</var> is 1, an MP 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.)</li> | ||
</ul></li> | |||
<li>If <var>MPDELAY</var> is set, consider reducing <var>SCHDOFL</var> to 1 or 0, since both parameters attempt to solve the same problem (too much MP subtask activation/deactivation). Using both parameters can reduce throughput or response times.</li> | |||
</ul> | </ul> | ||
==See also== | |||
The <var>[[MPDELAYZ parameter|MPDELAYZ]]</var> parameter provides the same functionality as <var>MPDELAY</var> for zIIP/SRB subtasks. | The <var>[[MPDELAYZ parameter|MPDELAYZ]]</var> parameter provides the same functionality as <var>MPDELAY</var> for zIIP/SRB subtasks. | ||
[[Category:System parameters]] | [[Category:System parameters]] | ||
[[Category:Parameters]] | [[Category:Parameters]] | ||
Latest revision as of 20:57, 2 August 2016
Delay before activating subtassk
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 MP subtasks when an extra one should be started based on SCHDOFL.
The default value of 0 means that if the number of units of work queued to MP subtasks exceeds some limit as indicated by the SCHDOFL parameter, an MP subtask is immediately started. The benefit of setting MPDELAY to a non-zero value is seen when a burst of work units arrive: it prevents the immediate starting of a large number of MP 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 MP subtasks can have non-trivial CPU costs.
Usage notes
- MPDELAY has no effect if either of these is true:
- MP/204 is not in effect in an Online (NMPSUBS is 0).
- The number of active subtasks (AMPSUBS) is set to 0 or 1. (If AMPSUBS is 1, an MP 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.)
- If MPDELAY is set, consider reducing SCHDOFL to 1 or 0, since both parameters attempt to solve the same problem (too much MP subtask activation/deactivation). Using both parameters can reduce throughput or response times.
See also
The MPDELAYZ parameter provides the same functionality as MPDELAY for zIIP/SRB subtasks.