MPDELAY parameter

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 that it prevents a large number of MP 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 MP subtasks can have non-trivial CPU costs.

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, it might make sense to reduce SCHDOFL to 1 or maybe even 0 as both parameters attempt to solve the same problem (too much MP subtask activation/deactivation) and using both can reduce throughput or response times.

The MPDELAYZ parameter provides the same functionality as MPDELAY for zIIP/SRB subtasks.