My mistake, xSDK only says you need to use the given communicators; it
doesn't say you need to use a duped version.
M3. Each xSDK-compatible package that utilizes MPI must restrict its MPI
operations to MPI communicators that are provided to it and not use directly
MPI_COMM_WORLD. The package should use configure tests or version tests to
detect MPI 2 or MPI 3 features that may not be available; it should not be
assumed that a full MPI 2 or MPI 3 implementation is available. The package can
change the MPI error-handling mode by default but should have an option to
prevent it from changing the MPI error handling (which may have been set by
another package or the application). The package should also behave
appropriately regardless of the MPI error handling being used. There is no
requirement that the package provide a sequential (non-MPI) version, although
this functionality is welcome, too. If the package provides a sequential
version, there is no requirement that it be compatible or usable with other
xSDK-compliant packages running without MPI.
Barry
> On Apr 3, 2018, at 4:22 PM, Matthew Knepley <[email protected]> wrote:
>
> On Tue, Apr 3, 2018 at 6:20 PM, Jed Brown <[email protected]> wrote:
> Derek Gaston <[email protected]> writes:
>
> > On Tue, Apr 3, 2018 at 4:06 PM Jed Brown <[email protected]> wrote:
> >
> >> Communicators should be cheap. One per library per "size" isn't a huge
> >> number of communicators.
> >>
> >
> > I agree - but that's not what we're getting here. We're getting one per
> > "object" (Mat / Preconditioner, etc.) associated with the library per
> > "size". If we can fix that I agree that there's no problem (we use a lot
> > of libraries... but not 2000 separate ones simultaneously!).
>
> So PETSc needs to dup and attach a hypre communicator because they
> aren't interested in doing it themselves. Not hard to implement, just
> mildly annoying.
>
> Can't someone tell them its an xSDK requirement?
>
> Matt
>
> --
> What most experimenters take for granted before they begin their experiments
> is infinitely more interesting than any results to which their experiments
> lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/
