[Haskell-cafe] Haskell performance question
Thomas Schilling
nominolo at googlemail.com
Thu Nov 8 14:24:07 EST 2007
On Thu, 2007-11-08 at 10:33 -0800, Dan Piponi wrote:
> I see lots of shootout examples where Haskell programs seem to perform
> comparably with C programs, but I find it hard to reproduce anything
> like those figures when testing with my own code. So here's a simple
> case:
>
> I have this C program:
>
> #include <stdio.h>
>
> #define n 100000000
>
> double a[n];
>
> int main()
> {
> int i;
> for (i = 0; i<n; ++i)
> {
> a[i] = 1.0f;
> }
> for (i = 0; i<n-1; ++i)
> {
> a[i+1] = a[i]+a[i+1];
> }
> printf("%f\n",a[n-1]);
> }
>
> And this Haskell program:
>
> import Data.Array.IO
> import Control.Monad
>
> n = 10000000
>
> main = do
> a <- newArray (0,n-1) 1.0 :: IO (IOUArray Int Double)
> forM_ [0..n-2] $ \i -> do { x <- readArray a i; y <- readArray a
> (i+1); writeArray a (i+1) (x+y) }
> x <- readArray a (n-1)
> print x
>
> Even though 'n' is 10 times bigger in the C program it runs much
> faster than the Haskell program on my MacBook Pro with Haskell 6.6.1.
> I've tried lots of different combinations of flags that I've found in
> various postings to haskell-cafe but to no avail.
>
> What flags do I need to get at least within a factor of 2 or 3 of C?
> Am I using the wrong kind of array? Or is Haskell always going to be
> 15-20 times slower for this kind of numerical work?
Wow. You should *really* try using GHC 6.8.1:
GHC 6.6.1 (-O2)
real 0m7.062s
user 0m5.464s
sys 0m0.288s
GHC 6.8.0.20071019
real 0m0.723s
user 0m0.616s
sys 0m0.100s
result is "2.0e7" for both
More information about the Haskell-Cafe
mailing list