IV81051: REDUCED PERFORMANCE ON COMPUTATIONALLY BOUND WORKLOADS WITH DOUB LY NESTED LOOPS ON JAVA 8

APAR status

• Closed as program error.

Error description

• Error Message: The problem will manifest as a performance
  regression between Java 8 GA and Java 8 SR1FP10 or later until
  Java 8 SR 3.
  .
  Stack Trace: N/A
  .
  For loops to suffer from this performance regression, there
  needs to be a large outer loop with a small, very frequently
  executed inner loop.
  

Local fix

• The affected method(s) will recover some of their performance if
  -Xjit:disableLoopVersioner,disableBlockSplitter are applied.
  These options do risk causing other performance regressions if
  there are other loops in the affected methods and applied
  globally to the application are likely to cause significant
  performance regressions.
  

Problem summary

• During development one of the loop optimization passes in the
  JIT was improved to improve the quality of code inside
  frequently executed loops. In some circumstances this new
  optimization can cause multiply indirected loads to be performed
  more times than necessary leading to performance degradation.
  

Problem conclusion

• The loop optimizations have been further enhanced to ensure they
  do not cause multiply indirected loads to be replicated within
  the generated loop bodies.
  .
  This APAR will be fixed in the following Java Releases:
     8    SR3       (8.0.3.0)
  .
  Contact your IBM Product's Service Team for these Service
  Refreshes and Fix Packs.
  For those running stand-alone, information about the available
  Service Refreshes and Fix Packs can be found at:
             https://www.ibm.com/developerworks/java/jdk/
  

Temporary fix

Comments

APAR Information

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

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

Fix information

• Fixed component name

  JIT

• Fixed component ID

  620700124

Applicable component levels

• R130 PSY

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