[GHC] #7602: Threaded RTS performing badly on recent OS X (10.8?)

[GHC]

#7602: Threaded RTS performing badly on recent OS X (10.8?)
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        Reporter:  simonmar        |            Owner:  thoughtpolice
            Type:  bug             |           Status:  new
        Priority:  highest         |        Milestone:  7.8.1
       Component:  Runtime System  |          Version:  7.7
      Resolution:                  |         Keywords:
Operating System:  MacOS X         |     Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown    |       Difficulty:  Unknown
       Test Case:                  |       Blocked By:  7678
        Blocking:                  |  Related Tickets:
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Comment (by ezyang):

 I must admit, I'm surprised that passing the thread-local state as a
 variable is not good performance-wise. At least within a function like
 evacuate, where everything ends up getting inlined into one giant function
 body, register pressure on x86_64 is low enough that I have seen
 (experimentally) that GCC is able to arrange for an extra parameter to not
 get spilled. Perhaps the situation is not so good across function call
 boundaries, but I don't see why it should necessarily be a problem.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7602#comment:29>
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