[GHC] #2140: cpuTimePrecision is wrong for me on Windows (XP)

[GHC]

#2140: cpuTimePrecision is wrong for me on Windows (XP)
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 Reporter:  guest           |          Owner:                
     Type:  bug             |         Status:  new           
 Priority:  normal          |      Milestone:  6.10 branch   
Component:  libraries/base  |        Version:  6.8.2         
 Severity:  normal          |     Resolution:                
 Keywords:                  |     Difficulty:  Unknown       
 Testcase:                  |   Architecture:  x86_64 (amd64)
       Os:  Windows         |  
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Comment (by guest):

 I use getCPUTime to measure the start and end times of some code I want to
 benchmark and need to know cpuTimePrecision to ensure that time
 quantisation is not a significant source of error and to normalise the
 times to some grokable number of "ticks".
 I don't know what part of windows API should be used for this, but 15.625
 mS seems too coarse resolution (at least 4 orders of magnitude too coarse
 assuming a non-brain dead OS) and the figure given by cpuTimePrecision is
 in any case wrong.

 If it can't be made right then it would be better not to have it at all,
 or have some function which determines it empirically (you could use
 unsafePerformIO to keep the existing API I guess).

 Unfortunately the mess that is MSDN doesn't make it at all easy to figure
 out what can or should be done about this. I can't figure it out but
 perhaps someone else knows.

 The queryPerformanceFrequency and queryPerformanceCounter functions seem
 to offer better resolution, but AFAICT measure "wall clock" time rather
 than CPU time and may not be available on all windows systems (according
 to MSDN).

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2140#comment:2>
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