[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):

 Simfactory doesn't parse parameter files, it parses thorn lists to
 add/remove thorns not supported on a machine.

 It is really necessary to have this mechanism? While some people want to
 run GRHydro with a single thread, others work on improving its performance
 and want to run it with multiple threads. So we can't make this thorn
 single-thread, and it wouldn't address this problem. In GRHydro, someone
 recently replaced the workshare constructs with explicit loops, addressing
 a shortcoming in the Intel compiler.

 I am really afraid that we are over-designing here. We are trying to
 anticipate problems, and are designing a non-trivial solution before we
 know what the problem is. I say we change the default number of threads,
 correct the (possibly wrong) MDB entries as we go along, and wait for
 feedback. We announce this change in a positive way and enjoy progress.

 Since this discussion is about a default setting, Simfactory's choice
 reflects the state of the art, namely that most machines these days
 require OpenMP to achieve good performance. This has changed from a few
 years ago, and hence changing the default makes sense. I outlined several
 ways in which users can choose their own settings overriding the default,
 and (as we all know) adding --num-threads to a submit command isn't that
 big of a deal -- we've been doing it for a long time ourselves.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/530#comment:10>
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