[Haskell-beginners] parallel program in haskell in 5 steps

[Jack Kennedy]

Does this happen for everyone, or just me?

On Tue, May 5, 2009 at 2:05 PM, Jack Kennedy <jack at realmode.com> wrote:

> I am compiling (Windows by the way) using the line from the tutorial:
> ghc -O2 --make par.hs -threaded
>
> and running with the line
>
> par +RTS -N2
>
> CPU usage for the process flits around a little, but stays in the 45% - 55%
> range.
>
>
> On Tue, May 5, 2009 at 12:51 PM, Michael Snoyman <michael at snoyman.com>wrote:
>
>> How are you running the program? You have to explicitly tell the
>> compiler/interpreter to use multiple system threads.
>>
>> Michael
>>
>> On Tue, May 5, 2009 at 10:19 PM, Jack Kennedy <jack at realmode.com> wrote:
>>
>>> In step 4 of Haskell in 5 Steps [
>>> http://haskell.org/haskellwiki/Haskell_in_5_steps],
>>> a parallel program is given. I changed it very slightly so it would run a
>>> long time (see below).
>>>
>>> It compiles and runs but my CPU meter is barely above 50%.  I have a dual
>>> core processor.
>>> What in the world would keep this program from completely saturating the
>>> CPU?
>>>
>>> import Control.Parallel
>>>
>>> main = a `par` b `pseq` print (a + b)
>>>     where
>>>         a = ack 4 10
>>>         b = ack 4 10
>>>
>>> fac 0 = 1
>>> fac n = n * fac (n-1)
>>>
>>> ack 0 n = n+1
>>> ack m 0 = ack (m-1) 1
>>> ack m n = ack (m-1) (ack m (n-1))
>>>
>>> fib 0 = 0
>>> fib 1 = 1
>>> fib n = fib (n-1) + fib (n-2)
>>>
>>>
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>>>
>>
>
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