[GHC] #9221: (super!) linear slowdown of parallel builds on 40 core machine

[GHC]

#9221: (super!) linear slowdown of parallel builds on 40 core machine
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              Reporter:  carter      |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  high        |        Milestone:  7.10.1
             Component:  Compiler    |          Version:  7.8.2
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:  Compile-    |       Blocked By:
  time performance bug               |  Related Tickets:  #910
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonmar):

 You should never have more capabilities than cores.

 It's hard to know where to set the default on the memory-vs-time tradeoff
 curve.  GHC has typically been quite conservative here.

 Personally I'd like to know why -j is hardly providing any benefit beyond
 2-3 cores, regardless of heap size settings.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9221#comment:16>
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