[petsc-dev] Subcomms

[Barry Smith]

On Jan 28, 2012, at 10:59 AM, Matthew Knepley wrote:

> 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's got it!  The slight difference is that I submit is that people who "start out with a bad design decision in the beginning, and refuse to change it for whatever reason" are fundamentally stupid even though they may be considered by most measures to be smart.  To me the "bad design decisions" are so blindly obviously wrong it is hard for me to label the people who "refuse to change it for whatever reason," anything but stupid, what other phrase should I use "smart in many ways but blindly stupid in this one regard?"


   Barry


> 
>    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