[petsc-dev] synchronized printing, singletons, and jumbled GAMG/BJacobi output

[Matthew Knepley]

On Fri, May 24, 2013 at 6:52 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> The output from '-pc_type gamg -ksp_view' in parallel is all jumbled up
> because every process prints on its own singleton (due to
> !same_local_solves), but the singletons aren't synchronized.
>
> I think we should:
>
> 1. Make BJacobi only print from rank 0.  We can have a verbose output
>    flag to print the O(P) data in case of different solvers in different
>    subdomains, but I think it can't be on by default.  Especially in the
>    case of GAMG, there isn't anything interesting from the others
>    because they have zero degrees of freedom.  I would like to apply
>    this change to 'maint', the other points below would be developed on
>    'master'.
>

Definitely.


> 2. Buffer and then synchronize on PetscViewerRestoreSingleton.  This
>    requires adding PetscViewerASCIISynchronizedVPrintf so that normal
>    PetscViewerASCIIPrintf on the singleton viewer will write to a
>    string.
>

I would rather replace the writes with SynchronizedPrintf()s. Why change the
semantics?


> 3. PetscViewerASCIISynchronizedPrintf is currently messy because it
>    writes eagerly on rank 0.  Is that behavior important?  We need some
>    way to make rank 0 of the singleton still write to a buffer and I'd
>    rather not convolute the logic further.  Is it okay if I make
>    synchronized writes always go to a buffer (even from rank 0)?  (This
>    means that in case of a crash part way through a synchronized write,
>    we'll have less output.  I don't see any other disadvantages.)
>

This is alright with me.


> 4. We have two incompatible (private) definitions of the _PrintfQueue
>    structure.  I would like to consolidate by just using a
>    PetscSegBuffer in both places.
>

Fine.

   Matt


> src/sys/fileio/mprint.h:
>
> struct _PrintfQueue {
>   char        *string;
>   int         size;
>   PrintfQueue next;
> };
>
> src/sys/classes/viewer/impls/vu/petscvu.c:
>
> struct _PrintfQueue {
>   char        string[QUEUESTRINGSIZE];
>   PrintfQueue next;
> };
>



-- 
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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