[ET Trac] [Einstein Toolkit] #530: Change default for --num-threads

[Einstein Toolkit]

#530: Change default for --num-threads
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  Reporter:  eschnett     |       Owner:  hinder  
      Type:  enhancement  |      Status:  assigned
  Priority:  major        |   Milestone:          
 Component:  SimFactory   |     Version:          
Resolution:               |    Keywords:          
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Comment (by eschnett):

 I am afraid that we are here over-designing something that is not really a
 problem at all. Do we know even of a single case where someone would be
 severely affected by changing the default?

 We don't go through these hoops when it comes to MPI processes. There is
 no "this thorn doesn't do MPI" flag. If a thorn can't handle MPI, it would
 check this at startup, and abort with an error. We could do the same with
 OpenMP, except that OpenMP is "backward compatible" in the sense that it
 doesn't break anything, it would just run a bit slower than naively
 expected.

 Having a single thorn disable OpenMP for a whole simulation is overkill.
 The thorn will still work fine with OpenMP. Whether this is acceptable or
 not depends on the user's settings and the user's expectations. Is there a
 thorn which should disable OpenMP today? Which would it be? AHFinderDirect
 comes to my mind... When it comes to performance problems, then e.g.
 CarpetIOASCII is a much bigger sinner with it's missing MPI
 parallelisation (it serialises output).

 I think we are just being afraid of taking this step. We are imagining
 problems, trying to design a perfect solution, and in the process
 complicate things for everybody and avoid progress for everybody. Let's
 just do it, and if it doesn't work out, let's listen to the complaints and
 address them. This is the development version, after all.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/530#comment:9>
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