[Haskell-cafe] why PArr slower than list ?

[Albert Lee]

I read the GHC/Data Parallel Haskell/GHC.PArr page
http://haskell.org/haskellwiki/Data_Parallel_Haskell/GHC.PArr

and make a simple test to compare the speed of PArr against List:

{-# OPTIONS -fparr -fglasgow-exts #-}
module Main where
import GHC.PArr
import System.CPUTime

dotp :: Num a => [:a:] -> [:a:] -> a
dotp xs ys = sumP [:x * y | x <- xs | y <- ys:]

main = do
  t1 <- getCPUTime
  print $ sum [x*y|x<-[1..90000]|y<-[1..90000]]
  t2 <- getCPUTime
  print $ dotp [:1..90000:] [:1..90000:]
  t3 <- getCPUTime
  print $ t2 - t1
  print $ t3 - t2

and I get the result:

*Main> main
243004050015000
243004050015000
384540000000
1701841000000

My laptop is macbook macosx 10.4.8 and ghc-6.8 , anything wrong or I missed ?