[Haskell-cafe] how to read CPU time vs wall time report from GHC?
Edward Z. Yang
ezyang at MIT.EDU
Sun Aug 14 20:23:55 CEST 2011
That is slightly odd. What CPU and operating system are you running on?
Include Kernel versions if Linux.
Excerpts from Wishnu Prasetya's message of Sun Aug 14 14:11:36 -0400 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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