Below is the program I am using.

I did ghc --make -threaded program.hs

then

./program +RTS -N2

I don't see any speed gain compared to N1.

Am I missing something?

import System.Time

import Control.Parallel

fib :: Int -> Int

fib 0 = 0

fib 1 = 1

fib n = fib (n-1) + fib (n-2)

mkList :: Int -> [Int]

mkList n = [1..n-1]

relPrime :: Int -> Int -> Bool

relPrime x y = gcd x y == 1

euler :: Int -> Int

euler n = length (filter (relPrime n) (mkList n))

sumEuler :: Int -> Int

sumEuler = sum . (map euler) . mkList

sumFibEuler :: Int -> Int -> Int

sumFibEuler a b = fib a + sumEuler b

parSumFibEuler :: Int -> Int -> Int

parSumFibEuler a b

= f `par` (e `pseq` (e + f))

where

f = fib a

e = sumEuler b

secDiff :: ClockTime -> ClockTime -> Float

secDiff (TOD secs1 psecs1) (TOD secs2 psecs2)

= fromInteger (psecs2 - psecs1) / 1e12 + fromInteger (secs2 - secs1)

r1 :: Int

r1 = sumFibEuler 38 5300

main :: IO ()

main = do

t0 <- getClockTime

pseq r1 (return())

t1 <- getClockTime

putStrLn ("Sum: " ++ show r1)

putStrLn ("time: " ++ show (secDiff t0 t1) ++ " seconds")