[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:  7.12.1
       Component:  Compiler          |                 Version:  7.8.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:  #910              |  Differential Revisions:
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Comment (by simonmar):

 @ezyang: I absolutely agree.  Parallelism within a single process is
 always going to be harder to scale than separate processes.  That said,
 there might still be low-hanging fruit (e.g. better default heap settings)
 for parallel compilation.

 I very much like `-j` in GHCi though - we cut the time to load a large
 project by 3x just by turning on `-j` in GHCi with some suitable heap
 settings (`-A256m`).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9221#comment:25>
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