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
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 the target number of threads on the zIIP offload queue before a non-SRB MP subtask will be dispatched to help the zIIP subtasks and, if started, how aggressively the non-SRB MP subtasks will pick up work from the zIIP offload queue. Setting a higher value of SCHDOFLS will make 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 of 2 means that if all zIIP subtasks are active and there are more than SCHDOFLS times AMPSUBZ units of work on the zIIP offload queue, a non-SRB MP subtask will be dispatched as needed and will perform work intended for zIIPs. .
SCHDOFLS has no effect if zIIP SRBs are not in use in an Online (NMPSUBZ=0) or if the number of active SRBs (AMPSUBZ) is set to 0 or if MP subtasks are not allowed to take work from zIIPs (SCHDOPT X'40' is set).
The SCHDOFL parameter and SCHDOFLZ parameter control the scheduling of zIIP/SRB and non-zIIP/non-SRB MP subtasks.