Why is this Haskell array filling operation so slow?

Question

For a specific task, I need a lot of fast, separate entries in a mutable array. To test performance, I used the following test:

size :: Int
size = 256*256*16

arr :: UArray Int Int
arr = runST $ do
    arr <- newArray (0,size) 0 :: ST s (STUArray s Int Int)
    forM_ [0..size] $ \i -> do
        writeArray arr i i 
    unsafeFreeze arr

arr_sum = foldl' (\ sum i -> sum + (arr ! i)) 0 [0..size-1]

main = print arr_sum

Here is the result:

vh:haskell apple1$ ghc -O3 bench.hs -o bench; time ./bench
Linking bench ...
549755289600

real    0m0.748s
user    0m0.697s
sys 0m0.048s

I suspected it should not take 0.7 to fill the 256 * 256 * 16 array in memory, so I tested the equivalent program in JavaScript:

size = 256*256*16;
x = new Array(size);
s = 0;
for (var i=0; i<size; ++i)
    x[i] = i;
for (var i=0; i<size; ++i)
    s += x[i];
console.log(s);

And the result:

vh:haskell apple1$ time node bench.js
549755289600

real    0m0.175s
user    0m0.150s
sys 0m0.024s

In C, time was 0.012s, which is a good lower bound.

#include <stdio.h>

#define SIZE (256*256*16)
double x[SIZE];

int main(){
    int i;
    double s = 0;
    for (i = 0; i<SIZE; ++i)
        x[i] = i;
    for (i = 0; i<SIZE; ++i)
        s += x[i];
    printf("%f",s);
};

, Haskell - , . , - , , foldl' forM_, , , , . , ?

Answer 1

GHC , , C. 3 , .

, Vector:

import qualified Data.Vector.Unboxed as V

size = 256*256*16 :: Int

doit = V.foldl' (+) 0 vec
  where vec = V.generate size id 

main = print doit

Answer 2

, . , -Wall ( , ):

module Main where

import Data.Array.Unboxed
import Data.Array.ST
import Data.Array.Unsafe
import Control.Monad.ST
import Control.Monad
import Data.List

size :: Int
size = 256*256*16

ar :: UArray Int Int
ar = runST $ do
    a <- newArray (0,size) 0 :: ST s (STUArray s Int Int)
    forM_ [0..size] $ \i -> do
        writeArray a i i 
    unsafeFreeze a

arrSum :: Int
arrSum = foldl' (\ s i -> s + (ar ! i)) 0 [0..size-1]

main :: IO ()
main = print arrSum

haskell node repsectively:

jberryman /tmp » time ./t         
-524288
./t  0.04s user 0.01s system 92% cpu 0.056 total
jberryman /tmp » time nodejs t.js 
549755289600
nodejs t.js  0.19s user 0.01s system 100% cpu 0.200 total

GHC 7.8 7.6 ( import Data.Array.ST hiding (unsafeFreeze), ).

: , ; , 32- haskell, JS, ; Integer .

-, , .

, C, .

Answer 3

, , . , , GHC -O2, . force-rrecomp:

ghc -fforce-recomp -O2 bench.hs -o bench

, #haskell @freenode, Cabal .