[GHC] #8224: Excessive system time -- new IO manager problem?

[GHC]

#8224: Excessive system time -- new IO manager problem?
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        Reporter:  rrnewton          |            Owner:
            Type:  bug               |           Status:  new
        Priority:  high              |        Milestone:  7.8.1
       Component:  Runtime System    |          Version:  7.7
      Resolution:                    |         Keywords:  IO Manager,
Operating System:  Linux             |  System Time
 Type of failure:  Runtime           |     Architecture:  x86_64 (amd64)
  performance bug                    |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by simonmar):

 The first safe call on each Capability will cause the creation of a new OS
 thread, which probably accounts for some of the cost.  From the strace
 profile it looks like there is some contention too.  It might be useful to
 do some mutex profiling to see what lock is being contended for - perhaps
 it is `all_tasks_mutex`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8224#comment:15>
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