https://bitbucket.org/petsc/petsc/issue/46/replace-petscsubcomm-with-the-information
On Jul 31, 2013, at 10:59 AM, Jed Brown <[email protected]> wrote: > Barry Smith <[email protected]> writes: > >> Jed, >> >> Hong and I were discussing MatGetRedundantMatrix() etc and she >> mention that you don't like PetscSubcomm. I suggested removing the >> PetscSubcomm object from PETSc but retaining the functionality of >> PetscSubcomm by putting the subcomm information into an MPI >> attribute inside an MPI_Comm (so this new comm behaves like a >> MPI_Comm subclass with extra data over a regular MPI_Comm) and >> having something like PetscCommSublimate(comm, …., &subcomm with >> attribute). Then in all the places in PETSc that take PetscSubcomm >> they would instead take a MPI_Comm and check for the attribute and >> use the additional information if it is there. > > I would be inclined to remove dependence on this extra information > whenever possible. For example, I think it is counter-productive in > MatGetRedundantMatrix because it imposes a distribution that has poor > locality. But if we need that extra information, or can do something > better if it is there, I prefer attaching it as an attribute to having a > wrapper (PetscSubcomm). > >> Managing destruction will be tricky due to possible reference >> loops but presumably we can figure out a way to do it. > > What is missing in the MPI attribute callbacks to implement reference > counting? (We already use it for this purpose.)
