MPDELAYZ parameter: Difference between revisions

From m204wiki
Jump to navigation Jump to search
m (minor wordsmithing)
m (wordsmithing)
Line 18: Line 18:
This parameter specifies the number of milliseconds to delay starting additional zIIP/SRB subtasks when an extra one should be started based on <var>[[SCHDOFLZ parameter|SCHDOFLZ]]</var>.</p>
This parameter specifies the number of milliseconds to delay starting additional zIIP/SRB subtasks when an extra one should be started based on <var>[[SCHDOFLZ parameter|SCHDOFLZ]]</var>.</p>
<p>
<p>
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 <var>SCHDOFLZ</var> parameter, a zIIP subtask is immediately started. The benefit of setting <var>MPDELAYZ</var> 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.</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>
<p>
<p>
<var>MPDELAYZ</var> has no effect if either of these is true: </p>
<var>MPDELAYZ</var> has no effect if either of these is true: </p>

Revision as of 19:53, 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.

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.

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.