Just to remove one variable: what happens if you run the same executable multiple times, rather than rebuilding it each time?

On Jan 15, 2017 6:34 PM, "Juan Luis Martty" <jmartty@hotmail.com> wrote:

Hello everyone,

I'm having a consistency issue with the following piece of code:

heavyAm = 500

lightAm = 1000

heavyCalc :: Int -> Int

heavyCalc s = sum [1..1000000*s]

parallel = (heavyCalc lightAm, heavyCalc heavyAm) `using` (parTuple2 rseq rseq)

For some reason, during runtime the RTS sometimes parallelizes the evaluation and sometimes it doesn't. I'm running with all the RTS/compile time options correctly afaik. Here is the output from a couple of runs of the program:

jmartty@walrus:~/hs/parallel$ stack build && time stack exec par-exe

Warning: File listed in par.cabal file does not exist: README.md

(500000000500000000,125000000250000000)

Computation time: 1.557007s

real    0m1.732s

user    0m2.528s

sys 0m0.464s

jmartty@walrus:~/hs/parallel$ stack build && time stack exec par-exe

Warning: File listed in par.cabal file does not exist: README.md

(500000000500000000,125000000250000000)

Computation time: 1.544837s

real    0m1.720s

user    0m2.544s

sys 0m0.712s

jmartty@walrus:~/hs/parallel$ stack build && time stack exec par-exe

Warning: File listed in par.cabal file does not exist: README.md

(500000000500000000,125000000250000000)

Computation time: 2.316537s

real    0m2.484s

user    0m2.592s

sys 0m0.680s

jmartty@walrus:~/hs/parallel$ stack build && time stack exec par-exe

Warning: File listed in par.cabal file does not exist: README.md

(500000000500000000,125000000250000000)

Computation time: 2.318514s

real    0m2.489s

user    0m2.612s

sys 0m0.688s

jmartty@walrus:~/hs/parallel$ stack build && time stack exec par-exe

Warning: File listed in par.cabal file does not exist: README.md

(500000000500000000,125000000250000000)

Computation time: 1.544975s

real    0m1.718s

user    0m2.512s

sys 0m0.456s

As you can see, sometimes wall time roughly equals userspace time, sometimes it doesn't (meaning it parallelized at least some amount). I'm running on a dual core machine under Ubuntu using stack with lts-7.14 (GHC 8.0.1) and parallel-3.2.1.0.

Regards,
Juan

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