A fix is available
APAR status
Closed as program error.
Error description
When z/OS (IEAVWUQ: WUQ add) detects a flood of SRBs it can start scheduling new SRBs at the scheduler's work unit (WEB) dispatching priority. If the scheduling work unit is currently promoted to dispatching priority (DPH) FF for local or CML lock contention as it does the schedule, the scheduled work can "inherit" that scheduler's promoted WEB DPH FF inadvertently. If the scheduled work persists as a long running SRB or multiple SRBs, the effects of it (them) inheriting DPH FF can be varied. Delay for CPU and system stall can be seen if multiple SRBs with DPH FF are created. EXTERNAL SYMPTOMS: System stall. VERIFICATION STEPS: 1) From system trace table, note CP on which the SRB in question is running. Presumably this is an SRB that is taking more CP than expected. 2) Issue: IPCS CBF LCCAnn where "nn" is the decimal number of the processor that the SRB was running on. Do: FIND CWEB within this LCCA report. 3) Issue: IPCS CBF xxxxxxxx STR(WEB) where xxxxxxxx is the address from LCCACWEB, obtained in step 2. Verify that the WEB contains the following field settings: CMAJO.... 00FF CMINO.... 00FF PCTRL.... 01000000 indicating that the unit of work is running at dispatching priority X'FF' and the WebPromotion_SRBsActive bit is ON. 4) If there is a match on these fields, then you have confirmed that the unit of work was running at an elevated priority due to detected SRB flooding. This priority should match the *normal* priority of the scheduling WEB. This leads to the question of whether the scheduling WEB had a normal DP of FF, or whether normally (in the absence of local/CML lock promotion) it runs at a lower DP. To get a probable indication of this, if you know what address space the scheduling unit of work lives in, check that address space's ASCBDPH (IP SUMM FORMAT report for that address space). If the DPH field is less than X'FF', then the scheduling unit of work probably normally runs at a priority lower than X'FF', in which case this APAR should help. Otherwise, if the scheduling unit of work's priority is normally X'FF', then this APAR will not help.
Local fix
Problem summary
**************************************************************** * USERS AFFECTED: Users running z/OS HBB7780 and above. * **************************************************************** * PROBLEM DESCRIPTION: A system can stall during a flood of * * SRBs, because an SRB is incorrectly * * promoted to the highest dispatching * * priority. * **************************************************************** * RECOMMENDATION: * **************************************************************** During a flood of SRBs, Supervisor performs SRB promotion, where an SRB will use its scheduler's workunit dispatching priority. If the SRB scheduling workunit got temporarily promoted during lock contention, the SRB will incorrectly inherit the scheduler's promoted dispatching priority. If the SRB is a long running SRB, the incorrect inherited dispatching priority can cause non-system level work to not run, resulting in a stalled system.
Problem conclusion
Fixed SRB promotion processing to use the SRB scheduling workunit's normal dispatching priority (as if it was not promoted) if the scheduling workunit dispatching priority was temporarily promoted during lock contention.
Temporary fix
********* * HIPER * *********
Comments
APAR Information
APAR number
OA49474
Reported component name
SUPERVISOR CONT
Reported component ID
5752SC1C5
Reported release
780
Status
CLOSED PER
PE
NoPE
HIPER
YesHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2015-12-04
Closed date
2016-01-15
Last modified date
2016-02-01
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
UA80346 UA80347 UA80348
Modules/Macros
IEAVEAT0 IEAVEDSR IEAVEGR IEAVEJST IEAVEMIN IEAVEMRQ IEAVESC0 IEAVESVC IEAVINIT IEAVLKRM IEAVMPWQ IEAVSCHA IEAVSCHD IEAVWUQA IEAWEBP
Fix information
Fixed component name
SUPERVISOR CONT
Fixed component ID
5752SC1C5
Applicable component levels
R7A0 PSY UA80346
UP16/01/27 P F601
R780 PSY UA80347
UP16/01/27 P F601
R790 PSY UA80348
UP16/01/27 P F601
Fix is available
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Document Information
Modified date:
01 February 2016