My experience with running parallel programs on dual processor machines is similar. With only two processors, one is always busy doing something for the OS. As a result, it rarely gets scheduled. You need a quad cpu to play with parallel programming. ____________________ David Place Owner, Panpipes Ho! LLC http://panpipesho.com d@vidplace.com On Jul 6, 2011, at 11:08 AM, Kees Bleijenberg wrote:

I've carefully followed the instructions in Real World Haskell for parallel sorting: In SortMain.hs 1. Set testfunction=sort Then del *.o (force recompilation) ghc --make -O2 sortMain.hs run SortMain and I get 500000 numbers => 3.9735 sec.

2. Set testFunction = parSort2 2 del *.o ghc -threaded --make -O2 sortMain.hs run SortMain +RTS -N2 -RTS, I get => 5.3 sec run SortMain +RTS -N1 -RTS, I get => 4.3 sec With the +RTS -s option I get 3 SPARK3 (3 converted, 0 pruned) All other testFunctions are worse.

I have a dual core computer that runs Windows XP. I've experimented a lot with par, pseq ... in other programs. I almost always get a few hundred sparks. Half of them are converted and the other half gets pruned. But I never got a faster program (then sequential).

What am I doing wrong, any ideas?

Kees

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