LI77032: SIMD PERFORMANCE ISSUE

Subscribe

You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • Performance degradation is seen when using -O3 -qhot related to
    SIMD copy of data.
    

Local fix

  • Insert a NOSIMD on affected loops.
    

Problem summary

  • PROBLEM DESCRIPTION:
    A performance degradation is observed when the compiler is
    vectorizing simple copy loops compared with the system memcpy
    routine.
    
    USERS AFFECTED:
    Users who use -O3 -qhot and above with the XL C/C++ for BG/Q,
    V12.1 compiler.
    

Problem conclusion

  • On BG/Q, it is observed that memcpy() is significantly faster
    than generating QPX simd instructions.  For that reason, the
    compiler will now always generate memcpy() transformations
    instead of vectorizing the loop, as long as there is no memory
    overlap between the source and target arrays.
    

Temporary fix

Comments

APAR Information

  • APAR number

    LI77032

  • Reported component name

    XL FORTRAN FOR

  • Reported component ID

    5799AH100

  • Reported release

    E10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-09-25

  • Closed date

    2012-11-23

  • Last modified date

    2012-11-23

  • 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

    XL FORTRAN FOR

  • Fixed component ID

    5799AH100

Applicable component levels

  • RE10 PSY

       UP



Rate this page:

(0 users)Average rating

Add comments

Document information


More support for:

XL Fortran for Blue Gene/Q

Software version:

ALL VERSIONS

Reference #:

LI77032

Modified date:

2012-11-23

Translate my page

Machine Translation

Content navigation