[GHC] #14981: GHC parallel GC is not doing well on modern many-core machine

[GHC]

#14981: GHC parallel GC is not doing well on modern many-core machine
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        Reporter:  varosi            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Runtime System    |              Version:  8.4.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by jberryman):

 I only spent a few minutes looking at the eventlog in threadscope, but the
 thing that looked instantly fishy to me was that it looks like we stop the
 world at every minor GC (there are only a dozen collections of gen 1).
 Another thing to observe is that it looks like the spark creation is
 healthy, and all work is sparked within the first third or so of program
 execution (i.e. those little pauses aren't yields because no work is ready
 to be done, which is what I thought might be happening at first glance.

 Supposedly RTS flags used were: `-N -A15m -qb0 -qn8`. Attaching op's
 screenshot from the reddit thread

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14981#comment:2>
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