CODEWITHSUNDEEP
loopsfortranopenmpnested-loopsfortran90
JRC
JRC

Reputation: 63

Fortran 90/95 OpenMP reduction with an array (sum)

I'm working on adding some OpenMP directives to a large set of fairly expensive nested loops. I believe I need to use a reduction clause with my directive since the operations on the array on not necessarily independent. However, when attempting to add the reduction directive my application core dumps (but does compile). I'm using IBM's XL Fortran compiler enabled with OpenMP 3.0. My (simplified) code is below:

!$omp parallel do reduction(+:f)  private(n,m,l,i,j,k, &
!$omp            parm,ista,iend,jsta,jend,ksta,kend)
do n=1,lm     !k
 do m=1,jm   !j
  do l=1,im !i

    if (val(l,m,n) .ne. zero) then

     jsta=max j bounds in box
     jend=min j bounds in box
     ista=max i bounds in box
     iend=min i bounds in box
     ksta=min k bounds in box
     kend=max k bounds in box

     do k=ksta,kend
      do j=jsta,jend
       do i=ista,iend

          parm = exp( -dx*(abs(i-l)) &
                      -dy*(abs(j-m)) &
                      -dz*(abs(k-n)))

          f(i,j,k) = f(i,j,k)+ val(l,m,n) * parm

       end do
      end do
     end do

    end if

  end do
 end do
end do

Where f has dimension (im,jm,lm). Is this simply an issue of syntax? I've been trying this out on several smaller, toy problems but I'm having trouble getting what I learn with a smaller test to apply in this context. For reference purposes I asked a similar question a few months back but the problem has changed slightly since then and I don't believe the solution is as straightforward now ( link ).

Thanks for any help/comments!

Upvotes: 1

Views: 2314

Answers (1)

n.a
n.a

Reputation: 105

I'm using Intel Fortran compiler, but I have had a similar experience like you, segmentation fault at runtime.

In my case, the following solves the problem, which increases thread stack size. I hope this helps.

[hoge@hoge]$ ulimit -s unlimited
[hoge@hoge]$ export OMP_STACKSIZE=1g # 1GB for thread stack size

Upvotes: 1

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