> On Jan 22, 2020, at 6:11 PM, Felix Huber <[email protected]>
> wrote:
>
> Hello,
>
> I currently investigate why our code does not show the expected weak scaling
> behaviour in a CG solver. Therefore I wanted to try out different
> communication methods for the VecScatter in the matrix-vector product.
> However, it seems like PETSc (version 3.7.6) always chooses either
> MPI_Alltoallv or MPI_Alltoallw when I pass different options via the
> PETSC_OPTIONS environment variable. Does anybody know, why this doesn't work
> as I expected?
>
> The matrix is a MPIAIJ matrix and created by a finite element discretization
> of a 3D Laplacian. Therefore it only communicates with 'neighboring' MPI
> ranks. Not sure if it helps, but the code is run on a Cray XC40.
>
> I tried the `ssend`, `rsend`, `sendfirst`, `reproduce` and no options from
> https://www.mcs.anl.gov/petsc/petsc-3.7/docs/manualpages/Vec/VecScatterCreate.html
> which all result in a MPI_Alltoallv. When combined with `nopack` the
> communication uses MPI_Alltoallw.
>
> Best regards,
> Felix
>
3.7.6 is a quite old version. You should consider upgrading
