Re: [Haskell-cafe] Haskell performance question

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

#define n 100000000

double a[n];

int main() { int i; for (i = 0; i

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?

I tried both, but it would be really helpful to see your command line options. I used: $ gcc -O3 ghc-bench.c -o ghcbC ghc-bench.c: In function ‘main’: ghc-bench.c:16: warning: incompatible implicit declaration of built-in function ‘printf’ $ ghc --make -O2 ghc-bench.hs and got: $ time ./ghc-bench 2.0e7 real 0m0.714s user 0m0.576s sys 0m0.132s $ time ./ghcbC 20000000.000000 real 0m0.305s user 0m0.164s sys 0m0.132s This is on a first-gen Macbook running Ubuntu. 1GB RAM. 1.83Ghz Core Duo $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.8.0.20071019 $ gcc --version gcc (GCC) 4.1.2 (Ubuntu 4.1.2-0ubuntu4) Copyright (C) 2006 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.