3.4. Array Sum Benchmark (Fortran version)

This benchmark computes the sum of two arrays and stores the result in an other array.

Note

You can dowload this code visiting the url http://pm.bsc.es OmpSs Examples and Exercises’s (code) link. The Array Sum benchmark is included inside the 01-examples’s directory.

In this case we annotate the algorithm using the Fortran syntax. The benchmark compute a set of array sums. The first inner loop initializes one array, that will be computed in the second inner loop. Dependences warrant proper execution and synchronization between initialization and compute results:

DO K=1,1000
   IF(MOD(K,100)==0) WRITE(0,*) 'K=',K
   ! INITIALIZE THE ARRAYS
   DO I=1, N, BS
      !$OMP TASK OUT(VEC1(I:I+BS-1), VEC2(I:I+BS-1), RESULTS(I:I+BS-1))&
      !$OMP PRIVATE(J) FIRSTPRIVATE(I, BS) LABEL(INIT_TASK)
      DO J = I, I+BS-1
         VEC1(J) = J
         VEC2(J) = N + 1 - J
         RESULTS(J) = -1
      END DO
      !$OMP END TASK
   ENDDO
   ! RESULTS = VEC1 + VEC2
   DO I=1, N, BS
      !$OMP TASK OUT(VEC1(I:I+BS-1), VEC2(I:I+BS-1)) IN(RESULTS(I:I+BS-1))&
      !$OMP PRIVATE(J) FIRSTPRIVATE(I, BS) LABEL(ARRAY_SUM_TASK)
      DO J = I, I+BS-1
         RESULTS(J) = VEC1(J) + VEC2(J)
      END DO
      !$OMP END TASK
   ENDDO
ENDDO ! K
!$OMP TASKWAIT

Goals of this exercise

• Code is completely annotated, you DON’T need to modify it.
• Review source code, check different directives and their clauses. Try to understand what they mean.
• Check different compiled versions (performance, instrumented & debug).
• Check other runtime options (schedulers, throttle,… ).
• Check (scalability), execute using different number of threads and compute speed-up.
• Get a task dependency graph to analyse dependences.
• Get different paraver traces and analyse them: use paraver configure files (.pcf) in order to visualize thread state, task name,…