On Tue, May 5, 2009 at 2:05 PM, Jack Kennedy <jack@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@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@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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