[aspect-devel] Performance issue with box geometry

[Wolfgang Bangerth]

On 06/09/2017 12:30 PM, Bart Niday wrote:
> I’m running simulations in a 3d box, using specified “Repetitions” for a mesh with an unequal number of cells in the X, Y, and Z-directions. When I specify enough repetitions, ASPECT reports spending a lot of time in setup - for a mesh with 1 million nodes, it’s spending 20% of runtime in “Initialization”.
> In comparison, with the same parameters and mesh size but without specifying repetitions “Initialization” takes less than 1% of time. From performance it looks like specifying a large number of repetitions causes memory usage problems.

While deal.II isn't necessarily intended to be used for very large 
coarse meshes (and instead for adaptively refined meshes starting from 
relatively small coarse meshes), the slowdown you observe is still 
clearly undesirable.

The initialization happens in core.cc between lines 227 and 665 of the 
current developer version. It would be very interesting to see which 
part of those 440 lines is the problem, and that should be easy to find 
out by putting
   computing_timer.enter_section("xxx1");  // or some other "xxx2","xxx3"
   ...
   computing_timer.exit_section();
blocks around groups of lines, and then looking for what "xxx*" blocks 
take long.

Anyone interested in trying this?

Best
  W.

-- 
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Wolfgang Bangerth          email:                 bangerth at colostate.edu
                            www: http://www.math.colostate.edu/~bangerth/