IBM Support

IV35862: LONG GC PAUSE TIMES DUE TO JIT ASSUMPTIONS CLEANUP

Subscribe to this APAR

By subscribing, you receive periodic emails alerting you to the status of the APAR, along with a link to the fix after it becomes available. You can track this item individually or track all items by product.

Notify me when this APAR changes.

Notify me when an APAR for this component changes.

 

APAR status

  • Closed as program error.

Error description

  • Error Message: N/A
    .
    Stack Trace: N/A
    .
    Symptoms of the issue are long GC pause times where verbose GC
    reports reasonable GC time but the overall pause time is
    unacceptable"
    

Local fix

  • The issue can be circumvented by using
    -Xjit:noRecompile,disableCHOpts,disableCHTable.
    Note however that in some cases this may reduce peak throughput
    of the application.
    

Problem summary

  • The JIT compiler can generate code that may become invalid in
    the future (for instance if the class hierarchy changes since
    the compilation took place). When such code is generated the JIT
    registers a "runtime assumption" with the runtime system. If the
    assumption is violated the JIT will take corrective actions
    (recompiling the method or patching the code).
    These runtime assumptions need to be cleaned-up when the method
    they belong to gets recompiled or unloaded. Depending on the
    number of assumptions being generated, in some cases the cleanup
    procedure may introduce larger than usual GC pauses.
    

Problem conclusion

  • This defect will be fixed in:
    7.0.0 SR4
    6.0.1 SR5
    6.0.0 SR13
    .
    The runtime assumption cleanup algorithm has been changed to
    reduce its overhead which in turn should reduce GC pauses.
    

Temporary fix

Comments

APAR Information

  • APAR number

    IV35862

  • Reported component name

    JIT

  • Reported component ID

    620700124

  • Reported release

    260

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2013-01-24

  • Closed date

    2013-04-18

  • Last modified date

    2013-04-18

  • 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

  • R260 PSY

       UP

  • R600 PSY

       UP

[{"Business Unit":{"code":"BU048","label":"IBM Software"},"Product":{"code":"SSC9HBA","label":"Just In Time (JIT) Compiler"},"Component":"","ARM Category":[],"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"260","Edition":"","Line of Business":{"code":"","label":""}}]

Document Information

Modified date:
18 April 2013