[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:  8.2.1
       Component:  Runtime System    |              Version:  7.7
      Resolution:                    |             Keywords:  IO Manager,
                                     |  System Time
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Runtime           |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9221             |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 In reply to comment:31

 > Hi, as a developer on 48-core machine, I upvote the issue. I can
 reproduce it with many programs, e.g. this trivial one:

 It is far from clear to me that we should expect the program you cited to
 run well with `-N`. It allocates heavily and `-N` will use parallel GC on
 a heavily imbalanced heap. Looking at the eventlog confirms that nearly
 all of the cores are simply waiting for GC. As expected disabling parallel
 GC with `+RTS -qg` drastically reduces system time due to reduced
 synchronization overhead.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8224#comment:33>
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