[petsc-users] Simple query about GPU usage in PETSc

[Matthew Knepley]

On Tue, Dec 18, 2012 at 9:17 PM, Gaurish Telang <gaurish108 at gmail.com> wrote:
> I am trying out PETSc's GPU features for the first time.
>
> After skimming, a paper on the PETSc-GPU interface.
> http://www.stanford.edu/~vminden/docs/gpus.pdf
>
> I just wanted to confirm whether the following observation is correct.
>
> Suppose I want to solve  Ax=b and set  the PETSc vector- and matrix-type
> from the command-line
>
> Then to make my code run on the GPU,  *all* I need to do is to
>     (1)  set the "-vec_type"  at the command-line as "seqcusp" or "mpicusp"
> (depending on whether I am using a single/multiple GPU process )
>     (2)  set the "-mat_type"  at the command-line as "seqaijcusp" or
> "mpiaijcusp" (depending on whether I am using a single/multiple CPU process
> )
>     (3)  Solving the system Ax=b is done the "usual" way (see below) i.e
> nothing CUDA specific.
>
>   ierr = KSPCreate(PETSC_COMM_WORLD,&ksp);CHKERRQ(ierr);
>   ierr = KSPSetOperators(ksp,A,A,DIFFERENT_NONZERO_PATTERN);CHKERRQ(ierr);
>   ierr = KSPGetPC(ksp,&pc);CHKERRQ(ierr);
>   ierr = PCSetType(pc,PCJACOBI);CHKERRQ(ierr);
>   ierr =
> KSPSetTolerances(ksp,1.e-5,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT);CHKERRQ(ierr);
>
>   if (nonzeroguess) {
>     PetscScalar p = .5;
>     ierr = VecSet(x,p);CHKERRQ(ierr);
>     ierr = KSPSetInitialGuessNonzero(ksp,PETSC_TRUE);CHKERRQ(ierr);
>   }
> ierr = KSPSolve(ksp,b,x);CHKERRQ(ierr);
>
> (4) Looking at the type of the vector and the matrix, PETSc hands over the
> control to the corresponding CUSP solver.

Yes, that should work.

   Matt

> Thank you,
>
> Gaurish



--
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
their experiments lead.
-- Norbert Wiener