IBM Support

Apparent hang or loop during DFSMShsm shutdown or periodically throughout the day

Question & Answer


During DFSMShsm shutdown processing, the consolidation of SMF type 30 records can cause the appearance of a loop condition.  Increased CPU usage is evident. The loop or hang can also exhibit itself periodically during the SMF INTERVAL timeframes throughout the day.


Excerpt from MVS Init and Tuning for DDCONS:
DDCONS  { (yes)}  { (no) }
Specifies whether duplicate EXCP entries for type 30 SMF records are to be consolidated.
When DDCONS(YES) is specified, SMF merges the EXCP count for these duplicate entries into one entry if the following information is the same:
- ddname
- Device class
- Unit type
- Channel address
- Unit address
Long-running jobs might take a long time to end in this case because of the building of the SMF type 30 records for a long-running job.

An indication of SMF consolidation would be an SRB mode loop in module IEEMB836 in the system trace table from a dump taken during the apparent loop condition.

Pros of DDCONS(YES):
Less SMF Type 30 records overall
Less SMF filling or SMF swapping rates
Cons of DDCONS(YES):
Takes more CPU time and usage during HSM shutdown
Takes more CPU time and usage during SMF consolidation intervals
Pros of DDCONS(NO):
Faster HSM shutdown
Less likelihood of periodic slowdowns
Cons of DDCONS(NO):
Lots more SMF type 30 records
Higher SMF filling or SMF swapping rates
The option of specifying NODETAIL and INTERVAL in the SYS1.Parmlib SMFPRMxx member would cause the EXCP section not to be written out to the Type30 subtype4 and subtype5 records, but it would still write the information to the Type30 subtype2 and subtype3 records. The difference in subtypes with the INTERVAL parameter is that the subtype2 and subtype3 records are written out after each interval while the subtype4 and subtype5 data is retained in the address space. With both NODETAIL and INTERVAL, the tables are emptied at the interval rate, so growth and slowdown does not happen.


Change the parameter to DDCONS(NO) in the SMFPRMxx member of SYS1.Parmlib as well as shorten the INTERVAL parameter.
If the INTERVAL must be static, change the parameter to DDCONS(NO) in the SMFPRMxx member of SYS1.Parmlib only.

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Document Information

Modified date:
07 March 2022