[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:  normal          |   Milestone:  _|_          
   Component:  Runtime System  |     Version:  7.7          
    Keywords:                  |          Os:  MacOS X      
Architecture:  x86_64 (amd64)  |     Failure:  None/Unknown 
  Difficulty:  Unknown         |    Testcase:               
   Blockedby:  7678            |    Blocking:               
     Related:                  |  
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Comment(by simonmar):

 Ok, so an inline `pthread_getspecific` is good, but it's still not ideal,
 because the compiler can't see the code inside the inline asm.  Multiple
 references to the TLS variable should not cause repeated reads, but with
 the inline `pthread_getspecific`, they will.

 However, this can be worked around in the code by loading the TLS variable
 into a local once at the start of the function.  I wouldn't object to
 this, it's less invasive than passing around the TLS variable as a
 parameter everywhere.  But we should peer at the asm before and after to
 make sure it's doing what we expect.

 Stealing the WebKit-reserved slot would probably work for now, until some
 library developer has the same idea, and then we have a bizarre bug
 waiting to happen.  I suppose I slightly prefer to use gcc for now, since
 we know it works, has good performance, and doesn't have this infelicity.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7602#comment:16>
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