[Dune] Shared memory capabilities?

[Jö Fahlke]

Am Wed, 29. Oct 2014, 09:04:26 +0100 schrieb Aleksejs Fomins:
> What are the current capabilities of Dune to deal with shared memory
> architectures? Is there a plan to implement it?
> 
> By shared memory I mean using all the memory of a node by all its
> processes to avoid communication between them

If you mean whether multithreading is supported: We are working on that in
EXADUNE, and Robert Klöfkorn has done some multithreading with the old
ALUGrid[1].  The current status is approximately:

* With the right gridmanager you can traverse the grid in multiple threads and
  do read-only operations in parallel.

* I would not try communication in parallel with anything else (although one
  thread communicating in parallel with other threads doning traversal should
  be possible in principle).

* YaspGrid works in with threading, although that isn't tested with the most
  recent changes.

* The old ALUGrid could be made to work with threading, but there were some
  patches needed.  These patches would disable caching, slowing alugrid down
  quite a bit.  I think less intrusive patches were possible if you could
  limit yourself never to use an ALUGrid-iterator in a thread other than the
  one it was created in.

* The new dune-alugrid module was supposed to improve multithreading, though I
  haven't tried that yet.  Probably the ALUGrid guys can tell you more.

It is probably not a good idea to use multithreading across multiple
NUMA-nodes, better use MPI for that.  Within one NUMA-node there can be
benefits though.

Regards,
Jö.

[1] http://www.iam.fmph.uniba.sk/amuc/_contributed/algo2012/zbornik/2Kloefkornf.pdf


-- 
Jorrit (Jö) Fahlke, Institute for Computational und Applied Mathematics,
University of Münster, Orleans-Ring 10, D-48149 Münster
Tel: +49 251 83 35146 Fax: +49 251 83 32729

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