IV02776: POOR PERFORMANCE DUE TO MANY FAILED JIT COMPILATIONS

APAR status

• Closed as program error.

Error description

• Error Message: As this is a silent performance issue, by default
  no messages will be generated. The issue can be diagnosed by
  using the following JIT command line option to generate a
  verbose log:
  -Xjit:verbose={compile*},vlog=vlog.txt
  The verbose log will show that many methods fail compilations
  repeatedly with an error code of compilationInterrupted.
  Example:
   (warm) Compiling
  java/lang/J9VMInternals.prepare(Ljava/lang/Class;)V  t=30
  ! java/lang/J9VMInternals.prepare(Ljava/lang/Class;)V
  code=0xFFFFFFFFFFFFFFFF compilationInterrupted
   (warm) Compiling
  java/lang/J9VMInternals.prepare(Ljava/lang/Class;)V  t=30
  ! java/lang/J9VMInternals.prepare(Ljava/lang/Class;)V
  code=0xFFFFFFFFFFFFFFFF compilationInterrupted
   (warm) Compiling
  java/lang/J9VMInternals.prepare(Ljava/lang/Class;)V  t=30
  ! java/lang/J9VMInternals.prepare(Ljava/lang/Class;)V
  code=0xFFFFFFFFFFFFFFFF compilationInterrupted
   (warm) Compiling
  java/lang/J9VMInternals.prepare(Ljava/lang/Class;)V  t=30
  ! java/lang/J9VMInternals.prepare(Ljava/lang/Class;)V
  code=0xFFFFFFFFFFFFFFFF compilationInterrupted.
  .
  Stack Trace: N/A
  .
  

Local fix

• A possible workaround is to reduce the optimization level of
  affected methods to 'cold' or even noOpt. Example:
  -Xjit:{myMethod}(optLevel=cold)
  This approach my not be feasible if very many methods are
  affected. Also, please note that this approach is likely to
  decrease performance as well, although to a lesser degree.
  

Problem summary

• The problem is caused by the JIT which uses an incorrect error
  code. When GC unloads classes the compilation in progress is
  aborted, but it will be retried. The error seen in the verbose
  log is 'compilationInterrupted'. Class unloading being a rather
  rare event the compilation retrial is expected to succeed. This
  is normal operation and isolated compilation failures with an
  error code of 'compilationInterrupted' are benign.
  In the problematic case the method was too complex for the JIT
  to compile at the desired optimization level. In such cases an
  appropriate error code is used and the JIT will retry the
  compilation at a lower optimization level. Due to a bug, an
  incorrect error code was used and the JIT was retrying the
  compilation at the same optimization level causing the
  compilation of the method to fail repeatedly.
  

Problem conclusion

• This defect will be fixed in:
  6.0.0 SR10
  .
  The JIT was changed to use the appropriate error code when a JIT
  compilation cannot be performed due to high complexity
  .
  To obtain the fix:
  Install build 20110523 or later
  

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

• R600 PSY

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