[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:  patch
        Priority:  normal            |        Milestone:  _|_
       Component:  Compiler          |          Version:  6.4.2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:  N/A               |       Blocked By:  8184
        Blocking:                    |  Related Tickets:
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Comment (by parcs):

 Replying to [comment:35 rrnewton]:
 > By the way, I've had various hard-to-pin-down problems with changing
 capabilities at runtime myself.
 >
 > Is it possible in this case to just disable the use of that feature for
 the initial release?  That is, you would have to use +RTS -N to get real
 speedup.  But, hey, it's kind of an advanced compilation feature anyway.
 In this scenario we could get a lot of testing experience with parallel
 builds without setNumCapabilities and then combine them when there is
 higher confidence.
 >
 >

 I don't mind going that route if the issue doesn't get sorted out soon. A
 subsequent point release of GHC could reinstate the feature (automatically
 setting the number of capabilities for the user), then. But I think I
 could fix it on time.

 ----

 Replying to [comment:34 simonmar]:
 > The changes to handle loops look OK to me, but I would test it on a GHC
 build to be sure. You want to build the whole of ghc/compiler with --make
 -O2; the build system doesn't do this so you have to make a command line
 by hand.

 At first I couldn't even get GHC to compile itself via `--make -O2`
 without `-j` (see #8184). Since that's been fixed I was able to build GHC
 via `--make -O2 -j` after a minor tweak in the code, so the loop handling
 should be solid now.

 On to the `setNumCapabilities` issue...

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/910#comment:38>
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