SCHDOPT parameter

Scheduler options

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 V6.1 or earlier

Description

Control of the main task scheduler operation and accounting.

• Setting X'10' is relevant to all sites.
• All other settings are relevant only to sites running MP/204.

Valid settings of SCHDOPT, which can be summed, are as follows:

Setting	Meaning
X'00'	No scheduler overhead tracking, no forced offload. This is the default.
X'01'	Maintain MAINTASK scheduler overhead.
X'02'	Do not allow the maintask to steal (run) work intended to run on an MP subtask. This parameter only has an effect if MP subtasks are defined and active (NMPSUBS parameter and AMPSUBS parameter). Setting this bit might cause increased CPU overhead because of the maintask going idle and then having to be redispatched. However, it might increase maintask responsiveness and provide somewhat better offload to MP subtasks. The maintask will always run maintask-only work before stealing any MP subtask work if this bit is not set.
X'04'	Defer page releases until server swap.
X'08'	Do server I/O on MP subtask. Note: As of version 7.6 of Model 204, this setting is disabled (has no effect).
X'10'	In CSLICE, check maximum values even if there is an SWAIT.
X'20'	Do not allow the maintask to steal (run) work intended to run on an zIIP SRB. This parameter only has an effect if zIIP SRBs are defined and active (NMPSUBZ parameter and AMPSUBZ parameter). Setting this bit might cause increased CPU overhead because of the maintask going idle and then having to be redispatched. However, it might increase maintask responsiveness and provide somewhat better offload to zIIP SRBs. The maintask will always run maintask-only work and MP subtask-only work before stealing any zIIP SRB work if this bit is not set.
X'40'	Do not allow the MP subtasks to steal (run) work intended to run on an zIIP SRB. This parameter only has an effect if both MP subtasks (NMPSUBZ parameter and AMPSUBZ parameter) and zIIP SRBs are defined and active (NMPSUBZ parameter and AMPSUBZ parameter). Setting this bit means that the MP subtasks can't pick up some of the CPU load if all zIIP SRBs are saturated. However, under Model 204 7.4 and 7.5 setting this bit would probably provide better zIIP utilization if there are MP subtasks also available. Under Model 204 7.6, even if this bit is not set, MP subtasks will only steal work from zIIP SRBs if those SRBs seem unable to keep up with the workload. As such, it is probably a bad idea to set this bit in Model 204 7.6 and later.
X'80'	Allow server swapping to be offloaded to zIIP processors. If you have SCHDOPT=80 set, then you probably want to set SCHDOPT1=01. Note: As of version 7.6 of Model 204, SCHDOPT X'80' and SCHDOPT1 X'01' are disabled (have no effect). The X'80' setting is only valid when CCASERVR is in memory (servers swapped into memory). If you set SCHDOPT=X'80' when CCASERVR is not in memory, the X'80' setting is reset and message 2914 is issued: SCHDOPT INDICATION OF SERVER SWAPPING DONE BY ZIIP IS ONLY VALID WHEN CCASERVR IS IN MEMORY Initialization then continues.