[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):

 One reason for extra user/system time that could account for your results
 in #910 is that if there isn't enough parallelism during GC then you'll
 have 30 threads spinning looking for work, and doing the occasional
 sched_yield().  Spinning accounts for the user time, the sched_yield()
 accounts for the system time.  Still, it does look like a lot, so it would
 be good to look at some !ThreadScope traces.

 That doesn't account for the 200ms in the empty program though, so there
 could be something else going on here.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8224#comment:9>
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