[GHC] #14714: RTS Timings on windows are somewhat unreliable

[GHC]

#14714: RTS Timings on windows are somewhat unreliable
-------------------------------------+-------------------------------------
           Reporter:  AndreasK       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Times given by the RTS are very unreliable on small scales.

 Part of that is I assume simply the lack of precision.
 But CPU Time often is reported higher than wall clock time (using the
 single threaded RTS) as well.

 Examples:
 {{{
 $ ./binary-trees 12 +RTS -t
 stretch tree of depth 13         check: -1
 ...
 long lived tree of depth 12      check: -1
 <<ghc: 43098232 bytes, 42 GCs, 345148/647488 avg/max bytes residency (2
 samples), 3M in use,
 0.000 INIT (0.000 elapsed),
 0.016 MUT (0.009 elapsed),
 0.000 GC (0.003 elapsed) :ghc>>

 $ ./binary-trees 12 +RTS -t
 stretch tree of depth 13         check: -1
 8192     trees of depth 4        check: -8192
 ...
 32       trees of depth 12       check: -32
 long lived tree of depth 12      check: -1
 <<ghc: 43098232 bytes, 42 GCs, 345148/647488 avg/max bytes residency (2
 samples), 3M in use,
 0.000 INIT (0.000 elapsed),
 0.000 MUT (0.010 elapsed),
 0.016 GC (0.003 elapsed) :ghc>>
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14714>
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