[petsc-dev] PetscSection

[Dmitry Karpeyev]

Any chance of a more intuitive name in place of PetscSF?


On Tue, Sep 10, 2013 at 8:43 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> Matthew Knepley <knepley at gmail.com> writes:
> >>   I was unclear.  The offset value should be in bytes from the beginning
> >> of the array, currently it is in ints from the beginning of the array.
> Ints
> >> is just plan confusing, Shri has to have this strange size sizeof(his
> >> struct)/sizeof(PetscInt) to indicate how big his chunk is.
> >
> >
> > No, its has nothing to do with Int. Where did this come from? In fact, I
> > use it all the time to mean Scalar offsets. It is
> > interpreter by the creator of the Section. I told him to put in bytes for
> > the sizes. Then you do not need any of that crap.
>
> PetscSF cannot currently scatter individual bytes (4 bytes minimum), and
> even if it could, it's a horribly inefficient representation (4 or 8
> bytes of metadata for each byte of payload).  The quick fix at that
> moment was to send in units of size PetscInt (the struct was always
> going to be divisible by that size).
>
> After looking at code with him yesterday, it looks like he just needs a
> separate Section for each of four different types of node.  Within each
> node type, the sizes are homogeneous (though there may be multiple
> structs at a vertex of the graph).  In that case, he can make an
> MPI_Datatype for sizeof(struct Node) bytes and communicate those.
> PetscSF should do fine with that.
>
> The indexing still needs the size of a unit, but there would be no stray
> sizeof(Int) running around.
>
>
> In that discussion, we also concluded that having the user add code to
> one big struct definition was a terrible approach and we should
> dynamically build structures by registration.  I pointed him to the
> monitor infrastructure in Parmod (like in TS ex11).
>
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