How to do time measurements in C and Fortran?


On BG/L we recommend to use the rts_get_timebase() function for timing purposes:
  • rts_get_timebase() returns the number of processor cycles executed since the partition was booted.
  • This number of clock ticks can be converted to seconds using the processor frequency (700 MHz).

Time measurement in C 

    #include <rts.h>

static double clockspeed=1.0e-6/700.0;

double bgl_wtime() {
  return ( rts_get_timebase() * clockspeed );
}
Time measurement in Fortran 
    module rts
! interface definition of rts_get_timebase, Fortran2003, available in XLF Version 9
  interface
    function rts_get_timebase() bind(c)
      use, intrinsic       :: iso_c_binding
      integer(c_long_long) :: rts_get_timebase
    end function rts_get_timebase
  end interface
end module rts

program rts_from_fortran
  use rts
  use, intrinsic :: iso_c_binding
  implicit none

  integer(c_long_long)  :: t1, t2
  real(kind=8)          :: clockspeed

  clockspeed = 700.0d6

  t1 = rts_get_timebase()
!      do some work
  t2 = rts_get_timebase()

  write(*,*) "Diff Ticks", (t2 - t1)
  write(*,*) "Total time", (t2 - t1)/clockspeed       ! Elapsed equal to CPU time
end program rts_from_fortran
  • To use RTS function calls, you need to link with the library librts.rts.a:
          blrts_xlf90 ... -L /bgl/BlueLight/ppcfloor/bglsys/lib -l rts.rts ...

last change 25.08.2005 | Ulrike Schmidt | Print