What a relief that no one castigated me for including a "goto"! I'm teaching out of Kupferschmid's "Classical Fortran", and he makes a rather compelling case that goto s actually more pedagogically sound (for beginners) than "do while"
Successive steps in the equilibration are time-dependant, so they're IMPOSSIBLE to parallelize. I suppose I could get around the re-initialization by including a "SINGLE" directive around the iteration control structure. Nathan On Fri, Nov 21, 2008 at 9:05 AM, <[EMAIL PROTECTED]> wrote: > Hi All > > I thing the problem could be the convergence "loop" test and the criation > of threads > > 10 converged = 1 > !$OMP PARALLEL > !$OMP DO > ..... > !$OMP ENDDO > !$OMP END PARALLEL > if(converged.eq.0) then > > goto 10 > endif > > Each time you "goto 10" > the compiler "create" and "initialize" the threads > and this is time comsuming. > try to change the convergence test to a > reduce operation this will > take time but not some much as !$OMP > PARALLEL > > I hope its help > > Renato Silva > > > > > Hi All, > > > > I'm getting to the end of a semester of computational physics at my > > institution, and thought it would be fin to close the semester with a > > discussion of parallel programming. Initially, I was simply planning to > > discuss MPI, but while reading through the gfortran man page I realized > > that > > gcc now supports OpenMP directives. > > > > Given that the machines my students are using are all dual core, I > started > > working on a simple example that I hoped would show a nice speedup from > > the > > "easy" library. > > > > The specific problem I'm working on is a 2-d solution to the laplace > > equation (electrostatics). The bulk of the computation is a recursion > > relation, applied to elements of a 2-d array, according to the following > > snippet. > > > > Of course, by now I should know that "simple" never really is. When I > > compile with gfortran and run with 1 or 2 cores (ie, OMP_NUM_THREADS=2, > > export OMP_NUM_THREADS) there is basically no difference in execution > > time. > > > > > > Any suggestions? I figured that this would be a simple example to > > parallelize. Is there a better example for OpenMP parallelization? Also, > > is there something obvious I'm missing in the example below? > > > > Nathan Moore > > > > integer,parameter::Nx=1000 > > integer,parameter::Ny=1000 > > real*8 v(Nx,Ny) > > integer boundary(Nx,Ny) > > > > v_cloud = -1.0e-4 > > v_ground = 0.d0 > > > > convergence_v = dabs(v_ground-v_cloud)/(1.d0*Ny*Ny) > > > > ! initialize the the boundary conditions > > do i=1,Nx > > do j=1,Ny > > v_y = v_ground + (v_cloud-v_ground)*(j*dy/Ly) > > boundary(i,j)=0 > > v(i,j) = v_y > > ! we need to ensure that the edges of the domain are held > > as > > boundary > > if(i.eq.0 .or. i.eq.Nx .or. j.eq.0 .or. j.eq.Ny) then > > boundary(i,j)=1 > > endif > > end do > > end do > > > > 10 converged = 1 > > !$OMP PARALLEL > > !$OMP DO > > do i=1,Nx > > do j=1,Ny > > if(boundary(i,j).eq.0) then > > old_v = v(i,j) > > v(i,j) = > > 0.25*(v(i-1,j)+v(i+1,j)+v(i,j+1)+v(i,j-1)) > > dv = dabs(old_v-v(i,j)) > > if(dv.gt.convergence_v) then > > converged = 0 > > endif > > endif > > end do > > end do > > !$OMP ENDDO > > !$OMP END PARALLEL > > if(converged.eq.0) then > > goto 10 > > endif > > _______________________________________________ > > Beowulf mailing list, Beowulf@beowulf.org > > To change your subscription (digest mode or unsubscribe) visit > > http://www.beowulf.org/mailman/listinfo/beowulf > > > -- - - - - - - - - - - - - - - - - - - - - - Nathan Moore Assistant Professor, Physics Winona State University AIM: nmoorewsu - - - - - - - - - - - - - - - - - - - - -
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