[GHC] #13830: '+RTS -s' gives incorrect value for work balance in some cases

[GHC]

#13830: '+RTS -s' gives incorrect value for work balance in some cases
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        Reporter:  duog              |                Owner:  duog
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Runtime System    |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Debugging         |  Unknown/Multiple
  information is incorrect           |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by duog):

 * owner:  (none) => duog


Comment:

 The number of garbage collection threads is limited to the number of cores
 right? I believe that this bug will result in the work balance being
 significantly under reported if the number of capabilities is much more
 than the number of gc threads.

 I don't expect dynamically changing capabilities is very common in the
 wild, but a number of capabilities several times the number of cores may
 be, I think I remember a blog post of Simon Marlow's saying that they do
 that at facebook.

 I'm assigning this to myself as I have a fix in mind: track a value like
 (or instead of) cumulative_par_max_copied_bytes.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13830#comment:2>
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