[GHC] #13246: hPutBuf issues unnecessary empty write syscalls for large writes

[GHC]

#13246: hPutBuf issues unnecessary empty write syscalls for large writes
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        Reporter:  nh2               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Runtime System    |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13245            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nh2):

 I've extracted the relevant code into a simple-to-run-and-modify single
 file, so that we can play around with it without recompiling `base`:

 * [https://gist.github.com/nh2/4cd40c2a4b15bf056bcae87907773786#file-ghc-
 bug-13246-repro-hs Without fix]
 * [https://gist.github.com/nh2/4cd40c2a4b15bf056bcae87907773786#file-ghc-
 bug-13246-fix-hs With fix]

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13246#comment:1>
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