OA60854: SMALL SPIKES IN LOCK STRUCTURE FALSE CONTENTION

APAR status

• Closed as fixed if next.

Error description

• RMF CF Activity report showed small spikes in false lock
  contention for the ISGLOCK str that was not impactful. A SLIP
  trap was used to trigger a dump on a spike >200. SYSXES LOCKMGR
  ctrace in the dump showed the false contention was related to a
  single resource and was NOT true false contention where 2
  resources hash to the same lock table entry with EXCL control.
  There is logic that keeps global management active when a
  resource is held EXCL to prevent thrashing in and out of global
  resource management. Although this is working as designed, we
  feel we can further lower the false contention rate in this
  specific case by returning to local management of the resource
  sooner with the changes introduced by apars OA59122/OA60394.
  
  VERIFICATION STEPS:
  1. RMF CF Activity report shows a low, spikey false contention
  rate for a lock structure.
  2. Trigger a sysplex wide dumps using a SLIP similar to this:
  SLIP
  SET,IF,N=(IXLA1SLM,FAE),DATA=(3R,GT,0000012C),ASID=(7),A=SVCD,JL
  NUC,SUM),REMOTE=(JL,SDATA),END
  with SYSXES LOCKMGR ctrace active for the lock structure.
  3. Verify there are not 2 resources both hashing to the same
  lock table entry (LTE) with EXCL control using the IPCS XESDATA
  LOCKRESOURCE LOCKMGR STRNAME(XXXXXX) DETAIL report
  4.If there are not 2 or more resources found, this apar is
  likely a contributing factor.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All users running in a Parallel Sysplex environment making   *
  * use of coupling facility (CF) lock structures for            *
  * sysplex-scope serialization functions.                       *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * XES Global Management may not end in a timely manner when    *
  * only one member other than the global manager has only an    *
  * exclusive interest in a resource. This may result in higher  *
  * false contention for the member with exclusive interest.     *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  Existing checks within Global Management processing can prevent
  Global Management from ending when only an exclusive interest in
  the resource remains. This can cause subsequent IXLLOCK requests
  by the member with the remaining interest to perform unnecessary
  XES signal processing and encounter false contention for the
  resource, contributing to higher false contention rates.
  
  This APAR is being closed FIN with concurrence from the
  submitting customer.  This means that a fix to this APAR is
  expected to be delivered from IBM in a release (if any) to be
  available within the next 36 months.
  

Problem conclusion

Temporary fix

Comments

• This APAR is being closed FIN with concurrence from the
  submitting customer.  This means that a fix to this APAR is
  expected to be delivered from IBM in a release (if any) to be
  available within the next 36 months.
  
  FINRESOLVED fix is in the base of release z/OS 3.1 (HBB77E0)
  

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

Applicable component levels