LI76992: OMP_SET_SCHEDULE CALL IS IGNORED

September 2012 Update for XL Fortran for Linux, V14.1
December 2012 Update for XL Fortran for Linux, V14.1
April 2013 Update for XL Fortran for Linux, V14.1
XL Fortran for Linux Fix Pack 4 (October 2013 Update) for 14.1
XL Fortran for Linux Fix Pack 5 (December 2013 Update) for 14.1
XL Fortran for Linux Fix Pack 6 (February 2014 Update) for 14.1
XL Fortran for Linux Fix Pack 7 (May 2014 Update) for 14.1

APAR status

• Closed as program error.

Error description

• When the OMP_SCHEDULE env variable is set, there exists a couple
  of 2 for each thread for the following test case.
  But when the OMP_SCHEDULE is unset and omp_set_schedule() is
  used, we don't see a couple of 2 per thread.
  
  
  ===== COMPILE COMMAND:
  xlf95_r -c -q64 -qsmp=omp:noopt -o helloworld.o helloworld.f95
  
  
  ===== TESTCASE:
  $ cat helloworld.f95
  PROGRAM helloworld
    use omp_lib
  
    IMPLICIT NONE
  
    INTEGER :: i, foo, ompmodifier
    integer(kind=omp_sched_kind) :: ompsched
    CHARACTER (LEN=16) :: ENVDATA
  
  !$OMP parallel
    PRINT *,'thread ',omp_get_thread_num(),' of
  ',omp_get_num_threads()
  !$OMP end parallel
  
    foo = 0
  
  !$OMP parallel
    CALL GETENV('OMP_SCHEDULE', VALUE=ENVDATA)
    PRINT *,'thread ',omp_get_thread_num(),' has env ', envdata
    call omp_set_schedule(omp_sched_static,2)
    call omp_get_schedule(ompsched,ompmodifier)
  
    PRINT *,'thread ',omp_get_thread_num(),' has schedule ',
  ompsched,' ', ompmodifier
  !$OMP do private(i) reduction(+:foo) schedule(runtime)
    DO i=1,6
      foo = foo + i
      PRINT *,'thread ',omp_get_thread_num(),' has item ', i
    END DO
  !$OMP end do
  
  !$OMP end parallel
  
  END PROGRAM helloworld
  $
  
  
  ===== ACTUAL OUTPUT:
  $export OMP_NUM_THREADS=2
  $./helloworld
   thread  0  of  2
   thread  1  of  2
   thread  0  has env
   thread  0  has schedule  1   2
   thread  1  has env
   thread  1  has schedule  1   2
   thread  1  has item  4
   thread  1  has item  5
   thread  1  has item  6
   thread  0  has item  1
   thread  0  has item  2
   thread  0  has item  3
  $
  
  
  
  ===== EXPECTED OUTPUT:
  Should give the same output as when OMP_SCHEDULE env variable is
  set to "static,2" as shown below because
  the program internally calls
  omp_get_schedule(omp_sched_static,2)
  
  $export OMP_NUM_THREADS=2
  $export OMP_SCHEDULE=static,2
  $./helloworld
   thread  0  of  2
   thread  1  of  2
   thread  0  has env static,2
   thread  0  has schedule  1   2
   thread  1  has env static,2
   thread  1  has schedule  1   2
   thread  1  has item  3
   thread  1  has item  4
   thread  0  has item  1
   thread  0  has item  2
   thread  0  has item  5
   thread  0  has item  6
  $
  

Local fix

• n/a
  

Problem summary

• USERS AFFECTED:
  Any OpenMP users that wish to change the runtime schedule of
  loops while the program is running is affected by this issue.
  
  PROBLEM DESCRIPTION:
  The omp_set_schedule call is effectively being ignored by the
  SMP Runtime.
  This means that users cannot dynamically change the schedule of
  runtime scheduled loops, as described in the OpenMP
  specification.
  

Problem conclusion

• The runtime is currently recording the values for the schedule
  and the modifier,
  as specified in the omp_set_schedule call. However, when it
  sets up the chunks for the parallel loop,
  it is not using the overwritten values. Instead it is using the
  default value provided in the OMP_SCHEDULE environment
  variable.
  This has been fixed.
  

Temporary fix

Comments

APAR Information

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

  IV20901

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

Fix information

• Fixed component name

  XL FORTRAN LINU

• Fixed component ID

  5725C7500

Applicable component levels

• RE10 PSN IV20901

     UP06/09/13