[Haskell-cafe] Unable to get parallelism using `par`

[C K Kashyap]

Hi,
I tried the first example from "A tutorial on Parallel and Concurrent
programming in Haskell" but I cant seem to get sparks to get converted to OS
threads.

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")
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