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LI77452: PERFORMANCE DEGRADATION WITH POPCNT ON POWER7

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You can track all active APARs for this component.

 

APAR status

  • Closed as program error.

Error description

  • A performance degradation is seen with the __popcnt4 and
    __popcnt8 population count functions when POWER7 hardware is
    targeted with the -qarch/-qtune options, and -qhot/IPA
    optimization is used.  Slower code is generated using
    the popcntb instruction instead of the popcntw/popcntd
    instructions.
    

Local fix

  • - Do not use higher -qhot levels, use -qhot=level=0
    

Problem summary

  • PROBLEM DESCRIPTION:
    Performance degradation with popcnt optimization.
    
    USERS AFFECTED:
    Customers who use popcnt instructions on POWER7.
    

Problem conclusion

  • The popcnt optimization on POWER7 has been disabled, since it
    is not profitable on POWER7.
    

Temporary fix

Comments

APAR Information

  • APAR number

    LI77452

  • Reported component name

    XL C/C++ FOR LI

  • Reported component ID

    5724X1400

  • Reported release

    B10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2013-06-11

  • Closed date

    2013-06-11

  • Last modified date

    2013-06-11

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

    IV29519

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

Fix information

  • Fixed component name

    XL C/C++ FOR LI

  • Fixed component ID

    5724X1400

Applicable component levels

[{"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Product":{"code":"SSXVZZ","label":"XL C\/C++ for Linux"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"B10","Line of Business":{"code":"LOB57","label":"Power"}}]

Document Information

Modified date:
14 October 2021