I'll cut to the chase. The short program below works perfectly: when I compile it with -O2 -threaded and run with +RTS -N2 command-line options, I get a nearly 50% real-time improvement:
$ time ./primes-test +RTS -N2 5001 real 0m9.307s user 0m16.581s sys 0m0.200s However, if I move the `parallelize' definition into another module and import that module, the performance is completely lost: $ time ./primes-test +RTS -N2 5001 real 0m15.282s user 0m15.165s sys 0m0.080s I'm confused. I know that `par` must be able work across modules boundaries, because Control.Parallel.Strategies is a module and presumably it works. What am I doing wrong? > module Main where > > import Control.Parallel > import Data.List (find) > import Data.Maybe (maybe) > > --import Parallelizable > parallelize a b = a `par` (b `pseq` (a, b)) > > test :: Integer -> Integer -> Integer > test n1 n2 = let (p1, p2) = parallelize > (product $ factors $ product [1..n1]) > (product $ factors $ product [1..n2]) > in p2 `div` p1 > > factors n = maybe [n] (\k-> (k : factors (n `div` k))) > (find (\k-> n `mod` k == 0) [2 .. n - 1]) > > main = print (test 5000 5001) _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
