[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 thoughtpolice):

 I investigated Mavericks and talked with Simon about this.

 10.9 is problematic. It still emits indirect jumps via a call through
 `%rdi` when using `__thread`, so it can't perform a simple direct
 load/store to a 'fast' location. You can also use
 `pthread_{get,set}specific`, but these are indirect dynamic calls too (and
 probably performs even worse.) Furthermore I can't find the source code
 for `pthread_getspecific` & co, so it's impossible to check if my 10.8 fix
 still works OK.

 We decided to:

   * Make the runtime use `__thread` on OS X for now. This cleans up the
 code, and in the future could be optimized by the compiler/runtime
 handling of TLS variables in future versions.
   * Document the fact OS X will suffer a performance regression with the
 `-threaded` garbage collector.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7602#comment:33>
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