[petsc-dev] ugly shit

[Barry Smith]

On Nov 10, 2011, at 4:10 PM, Jed Brown wrote:

> On Thu, Nov 10, 2011 at 16:05, Barry Smith <bsmith at mcs.anl.gov> wrote:
>   You could have ./configure check for MPI_IN_PLACE and generate an error if it doesn't exist.  But do we want to say PETSc requires MPI 2.0 (or at least parts of it)????  Since we already have support for not having MPI_IN_PLACE I'd only like to remove that extra support if we knew that all (sane) users had access to MPI_IN_PLACE. Do we know this?
> 
> If we found an implementation that doesn't have it, we could define the MPI_IN_PLACE value and have our own wrapper that did the right thing (allocated the work array).

   I don't see this being simple. We would need to implement many MPI functions that take MPI_IN_PLACE.

>  
> 
> 
> > In general, can we rely on any MPI-2.0 features that have been implemented in mpiuni and remove the macro checking?
> 
>    I don't have a clue what parts of MPI-2.0 that MPIUni does or does not support :-(.  I'm afraid we'll need to find out one operation at a time. It definitely doesn't have the one-sided stuff, can/should that be added? I don't see a big upside in putting the one-sided stuff into MPI uni.
> 
> MPI one-sided is normally used to talk to remote processes, much like MPI_Send, which we currently define to produce an error if called. I think it would make sense to do the same thing with the one-sided stuff.