IJ53085: DEBUG MODE WITH AN AGENT ON POWER MAY GIVE VERY POOR PERFORMANCE

APAR status

• Closed as program error.

Error description

• Error Message: Running in debug mode with a monitoring agent ran
  so slowly that the customer reported the JVM as hung.
  .
  Stack Trace: N/A
  .
  

Local fix

• Using the default code cache segment size may help avoid the
  problem. The problem is made worse if larger segment sizes are
  set using the -Xcodecache option.
  The problem can be avoided by not used debug mode and a
  monitoring agent at the same time.
  

Problem summary

• The problem is triggered by the agent performing class
  redefinition while the JVM is running in debug mode. In debug
  mode redefinition causes the JIT code cache to be emptied and
  reset. An error in this code caused the cache segments in use at
  that time to be marked as full when running on platforms that
  require trampolines. If all code cache segments were in use at
  the time of the redef then the entire code cache becomes
  unusable and all methods must then run in the interpreter. Using
  larger than default segment sizes increases the likelihood that
  all the segments will have been allocated at the time of the
  class redefinition.
  

Problem conclusion

• The code has been changed so that the code cache segments are
  correctly reset to empty.
  https://github.com/eclipse-openj9/openj9/pull/20614
  .
  This APAR will be fixed in the following Releases:
  .
  IBM Semeru Runtimes
  IBM SDK, Java Technology Edition
     8    SR8 FP40  (8.0.8.40)
  .
  Downloads and supplementary documentation can be found at the
  following locations:
  - For non z/OS operating systems:
    - IBM Semeru Runtimes, Version 11 and later
      https://www.ibm.com/semeru-runtimes/downloads/
    - IBM SDK, Java Technology Edition, Version 8
      https://www.ibm.com/support/pages/java-sdk-downloads/
  - For the z/OS operating system:
    - Java SDK Products on z/OS
      https://www.ibm.com/support/pages/java-sdk-products-zos
  

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