[GHC] #910: --make should have a -j flag for parallel building

[GHC]

#910: --make should have a -j flag for parallel building
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        Reporter:  igloo             |                Owner:
            Type:  feature request   |               Status:  closed
        Priority:  normal            |            Milestone:  ⊥
       Component:  Compiler          |              Version:  6.4.2
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:  N/A
      Blocked By:  8184, 8235        |             Blocking:
 Related Tickets:  #9221             |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nh2):

 @rrnewton: That may or may not be a good idea - since tools like stack
 already do a `-j` on the package level, it seems that the best results can
 be achieved if such tools are aware of GHC's `-j` and use it correctly
 (e.g. you'd probably not want full `-j` for both stack and GHC as that
 would give you N*N threads and a lot of overhead) - so it may be worth
 more pushing for these tools to use GHC's `-j`.

 Also, if there was a `GHC_MAKE_CORES` env var, and `-j` was also given,
 which one would take precedence?

 To answer one of your questions directly, most of these tools accept a
 `--ghc-options` flag, e.g. you can do `stack build --ghc-options="-j4"`.

 I think another reason why not all tools use `ghc -j` is because of #9221.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/910#comment:64>
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