[petsc-dev] Expensive VecDuplicate_MPI_DA

[Junchao Zhang]

I met an expensive VecDuplicate. See the attached call
stack. VecDuplicate_MPI_DA indirectly calls MPI_Allreduce/Allgather to
build the vector's layout, but it then immediately destroys it
with VecGetLayout & VecSetLayout. Is it wrong?
src/dm/impls/da/dadist.c
PetscErrorCode  VecDuplicate_MPI_DA(Vec g,Vec *gg)
{
  PetscErrorCode ierr;
  DM             da;
  PetscLayout    map;

  PetscFunctionBegin;
  ierr = VecGetDM(g, &da);CHKERRQ(ierr);
  ierr = DMCreateGlobalVector(da,gg);CHKERRQ(ierr);
  ierr = VecGetLayout(g,&map);CHKERRQ(ierr);
  ierr = VecSetLayout(*gg,map);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

--Junchao Zhang
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