LI73257: CALLS TO _GETPID CAUSING PERFORMANCE ISSUE

July 2008 Update for XL Fortran Advanced Edition for Linux, V11.1
February 2010 Update for XL Fortran Advanced Edition for Linux, V11.1
June 2009 Update for XL Fortran Advanced Edition for Linux, V11.1
February 2011 Update for XL Fortran Advanced Edition for Linux, V11.1
March 2008 Update for XL Fortran Advanced Edition for Linux, V11.1
November 2008 Update for XL Fortran Advanced Edition for Linux, V11.1

APAR status

• Closed as program error.

Error description

• Multiple calls to _getpid by the omp_get_thread_num function are
  affecting performance.  The following test case demonstrates the
  performance issue when run with xlsmp V1.7.0.3 vs. xlsmp
  V1.6.0.3
  
  ====  TEST CASE  ====
  
     program testcase
     parameter(NREP=10000000)
     real*8 t0,t1,tt,timef
     t0=timef()
     do irep=1,nrep
       call z(mythrd)
     enddo
     t1=timef()
     tt=(t1-t0)/1000
     write(6,'(a,f8.2)') "time = ",tt
     end
     subroutine z(mythrd)
       integer omp_get_thread_num
       mythrd=omp_get_thread_num()
     end
  

Local fix

• N/A
  

Problem summary

• USERS AFFECTED:
  Users of OpenMP that make many calls to omp_* routines
  
  PROBLEM DESCRIPTION:
  The SMP runtime is calling getpid inside the omp_ routines
  to determine if the user has forked.  This causes a slowdown on
  these routines.
  

Problem conclusion

• Remove these calls and defer the detection of fork() calls
  until the next parallel region is reached.
  

Temporary fix

Comments

APAR Information

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

  IZ13827

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

Fix information

• Fixed component name

  XL FORTRAN RHEL

• Fixed component ID

  5724S7410

Applicable component levels

• RB10 PSN IZ13827

     UP06/09/13