[GHC] #3553: parallel gc suffers badly if one thread is descheduled

[GHC]

#3553: parallel gc suffers badly if one thread is descheduled
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        Reporter:  simonmar          |            Owner:  simonmar
            Type:  bug               |           Status:  closed
        Priority:  normal            |        Milestone:  6.12.2
       Component:  Runtime System    |          Version:  6.10.4
      Resolution:  fixed             |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by tibbe):

 > I noticed that if I change nofib/parallel/ray to do its work in a
 separate thread (see diff), that this "last core slowdown" completely
 vanishes. Can anybody explain this massive variance?

 It could be because main runs in a bound thread. Why that makes a huge
 difference I'm not sure (more context switching?), but that's a likely
 cause.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3553#comment:11>
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