SCHDOFLZ parameter

Threshold for activating zIIP subtasks

Summary

Default value

2

Parameter type

System

Where set

On User 0's parameter line or reset by system manager.

Related products

All

Introduced

Model 204 V7.4

Description

Applies to z/OS only

On a z/OS system, Model 204 zIIP support enables you to offload Model 204 work from regular processors to zIIP processors.

SCHDOFLZ specifies the target number of threads on the zIIP offload queue per active task. Setting this parameter makes the Model 204 zIIP subtask scheduler more responsive to instantaneous increases in load.

The default value of 2 means that if there are more than twice as many units of zIIP offloadable work waiting to be processed in a zIIP subtask as there are active subtasks, and fewer than AMPSUBZ subtasks are currently running, another zIIP offload subtask is activated.

SCHDOFLZ has no effect if zIIP SRBs are not in effect in an Online (NMPSUBZ=0) or if the number of active SRBs (AMPSUBZ) is set to 0. If AMPSUBZ=1, a zIIP subtask is activated as soon as there is any offloadable work and then runs until there is no more offloadable work for it to process. So with AMPSUB=1, SCHDOFLZ does not affect any zIIP subtask activation decisions. However, under Model 204 7.5 and 7.6, it would affect a non-SRB MP subtask activation and zIIP assistance decisions. Under Model 204 7.7 and later, this aspect of SCHDOFLZ as been subsumed by SCHDOFLS.

The SCHDOFL parameter performs the same function as SCHDOFLZ for non-SRB MP subtasks and the SCHDOFLS parameter controls how aggressively MP subtasks will be started to help zIIP subtasks out and how aggressively MP subtasks will take work from zIIP subtasks.