[GHC] #12424: RTS stats show wrong productivity.

[GHC]

#12424: RTS stats show wrong productivity.
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           Reporter:  vagarenko       |             Owner:
               Type:  bug             |            Status:  new
           Priority:  normal          |         Milestone:
          Component:  Runtime System  |           Version:  8.0.1
           Keywords:                  |  Operating System:  Windows
       Architecture:  x86_64 (amd64)  |   Type of failure:  None/Unknown
          Test Case:                  |        Blocked By:
           Blocking:                  |   Related Tickets:
Differential Rev(s):                  |         Wiki Page:
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 I have this report after runnig my program:
 {{{
   INIT    time    0.000s  (  0.001s elapsed)
   MUT     time   29.344s  ( 56.484s elapsed)
   GC      time    4.306s  (  1.589s elapsed)
   EXIT    time    0.000s  (  0.001s elapsed)
   Total   time   33.649s  ( 58.075s elapsed)

   Alloc rate    1,530,969,741 bytes per MUT second

   Productivity  87.2% of total user, 50.5% of total elapsed
 }}}

 Elapsed productivity is wrong.

 It should be `MUT elapsed / Total elapsed = 56.484 / 58.075 = 0.972`

 but it looks like `MUT user / Total elapsed = 29.344 / 58.075 = 0.505`

 Looks like the code at
 https://github.com/ghc/ghc/blob/a88bb1b1518389817583290acaebfd6454aa3cec/rts/Stats.c#L702-L704
 uses wrong numerator for elapsed value.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12424>
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