[petsc-dev] VecScatter scaling problem on KNL

Mark Adams mfadams at lbl.gov
Thu Mar 9 16:26:52 CST 2017

>      Matt is right,
>      You should definitely try this before writing additional code. But you need to put it in the code so it affects just this one scatter, not all the scatters. So in the place where you create this "all to all" vector scatter do the following.
>     PetscOptionsSetValue(NULL,"-vecscatter_alltoall","true");
>     VecScatterCreate...
>     PetscOptionsClearValue(NULL,"-vecscatter_alltoall")
>    You need to possibly change it slightly for different PETSc versions or Fortran.
>     Please let us know how it goes,

Yes, thanks. I've told them to do this after Matt convinced me that
this is really that simple.  And this is a good suggestion on how to
target just one VecScatter. I was going to use a prefix, but this is
less error prone.

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