[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 Austin Seipp <austin@…>):

 In [changeset:"28b031c506122e28e0230a562a4f6fd3d0256d0c/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="28b031c506122e28e0230a562a4f6fd3d0256d0c"
 Refactor GCTDecl.h, and mitigate #7602 a bit

 This basically cleans a lot of GCTDecl up - I found it quite hard to
 read and a bit confusing. The changes are mostly cosmetic: better
 delineation between the alternative cases and light touchups, and tries
 to make every branch as consistent as possible.

 However, this patch does have one significant effect: it will ensure
 that any LLVM-based compilers will use __thread if they support it.
 Before, they would simply always use pthread_getspecific and
 pthread_setspecific, which are almost surely even *more* inefficient.

 The details are a bit too long and boring to go into here; see #7602.
 After talking with Simon, we decided to play it safe - __thread can at
 least be optimized by future clang releases even further on OS X if they
 choose, and it's safer until we can investigate the pthread
 implementation further on Mavericks.

 For Linux, the story isn't so bleak if you use Clang (for whatever
 reason) - Linux directly writes to `%fs` for __thread slots (while OS X
 will perform a load followed by an indirect call.) So it should still be
 fairly competitive, speed-wise.

 Signed-off-by: Austin Seipp <austin at well-typed.com>
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7602#comment:35>
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