[petsc-dev] Subcomms

[Matthew Knepley]

On Sat, Jan 28, 2012 at 8:00 AM, Mark F. Adams <mark.adams at columbia.edu>wrote:

>
> On Jan 27, 2012, at 8:22 PM, Barry Smith wrote:
>
> >
> > On Jan 27, 2012, at 6:36 PM, Mark F. Adams wrote:
> >
> >>
> >> On Jan 27, 2012, at 6:58 PM, Jed Brown wrote:
> >>
> >>> On Fri, Jan 27, 2012 at 17:48, Matthew Knepley <knepley at gmail.com>
> wrote:
> >>>  Is now the right time. Shouldn't we wait until MPI's replacement is
> working and do things with that model?
> >>>
> >>> I'm laughing. Am I supposed to be?
> >>>
> >>> I'm laughing too.
> >>>
> >>> There isn't going to be a replacement for MPI until the smart people
> that understand parallel programming, performance, and libraries start
> working on something other than MPI. But most of those people are on the
> MPI Forum, trying to improve MPI. Now we need a good model for threads, and
> that might not be based on MPI, but it sure looks like the large-scale
> distributed-memory model will be MPI for the foreseeable future.
> >>>
> >>
> >> I don't think its a matter of smart people not having worked on this,
> they have IMO, its just a hard problem.
> >
> >   I disagree; it is not necessarily hard, it is just that the non-MPI
> people are pretty fucking stupid.
> >
>
> It is not hard, intellectually intriguing, fundable, and smart people
> won't do it.  What am I missing?


I think Barry's point is that this is another case where, no matter how
smart or motivated you are, if you start
out with a bad design decision in the beginning, and refuse to change it
for whatever reason, you will not
succeed.

   Matt


> >   Barry
> >
> >>
> >>>
> >>> As for sources of parallel errors, yes, it's somewhat tricky, but as
> long as the model is to get a sub-object out of a bigger one (submatrix,
> coarse level, etc), I think we can manage it. At any particular time, the
> user should still be looking at essentially single-comm collections of
> objects, but not all processes will end up being called in every context.
> >>
> >
> >
>
>


-- 
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
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