[Haskell-cafe] how to read CPU time vs wall time report from GHC?

Wishnu Prasetya s.w.b.prasetya at uu.nl
Sun Aug 14 20:11:36 CEST 2011

Hi guys,

I'm new in parallel programming with Haskell. I made a simple test 
program using that par combinator etc, and was a bit unhappy that it 
turns out to be  slower than its sequential version. But firstly, I dont 
fully understand how to read the runtime report produced by GHC with -s 

   SPARKS: 5 (5 converted, 0 pruned)

   INIT  time    0.02s  (  0.01s elapsed)
   MUT   time    3.46s  (  0.89s elapsed)
   GC    time    5.49s  (  1.46s elapsed)
   EXIT  time    0.00s  (  0.00s elapsed)
   Total time    8.97s  (  2.36s elapsed)

As I understand it from the documentation, the left time-column is the 
CPU time, whereas the right one is elapses wall time. But how come that 
the wall time is less than the CPU time? Isn't wall time = user's 
perspective of time; so that is CPU time + IO + etc?

Any help?


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