SCHDOFLS parameter

Threshold for task stealing zIIP work

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 V7.7

Description

This parameter 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. SCHDOFLS specifies both of the following:

• The target number of threads on the zIIP offload queue before a non-SRB MP subtask is dispatched to help the zIIP subtasks.
• If started, how aggressively non-SRB MP subtasks pick up work from the zIIP offload queue.

Setting a higher value of SCHDOFLS makes the non-SRB MP subtasks more reticent to help SRB subtasks out, ensuring better zIIP offload (though possibly adversely affecting performance should the zIIPs get overloaded).

The default value, 2, means that if all zIIP subtasks are active and there are more than SCHDOFLS * AMPSUBZ units of work on the zIIP offload queue, a non-SRB MP subtask is dispatched as needed and performs work intended for zIIPs.

SCHDOFLS has no effect if any of these is true:

• zIIP SRBs are not in use in an Online (NMPSUBZ is 0).
• The number of active SRBs (AMPSUBZ) is set to 0.
• MP subtasks are not allowed to take work from zIIPs (SCHDOPT X'40' is set).

SCHDOFL and SCHDOFLZ control the scheduling of zIIP/SRB and non-zIIP/non-SRB MP subtasks.