[Haskell-cafe] Slow IO?

[Steve]

On Wed, 2009-09-02 at 11:55 +0800, Steve wrote:
> On Tue, 2009-09-01 at 08:45 +0400, Eugene Kirpichov wrote:
> > Hm, on my machine Don's code has exactly the same performance my code above.
> That's strange.
> 
> > Also, replacing the 'test' and 'parse' functions with this one
> > 
> > add :: Int -> Int -> S.ByteString -> Int
> > add k i s = fst $ S.foldl' f (i, 0) s
> >   where f (!i, !n) '\n' | n`divisibleBy`k = (i+1, 0)
> >                         | otherwise       = (i,   0)
> >         f (!i, !n) w  = (i, 10*n+ord w-ord '0')
> > 
> > increases performance by another 15% (0.675s vs 0.790s)
> 
> On my system I get a 50% slowdown using this add function!
> 
> I guess is just shows that benchmarking code on one single
> CPU/memory/OS/ghc combination does not give results that apply widely.
> I'm using:
> AMD Athlon X2 4800
> 2GB memory
> Linux (Fedora 11, 64-bit version)
> ghc 6.10.3

I should have also said that the test method and test data is important
too.

This is what I have been using:
$ time ./0450 < 0450.input.data
and looking at the 'real' value.

The file 0450.input.data is generated with a Python script:
#!/usr/bin/env python
'''
generate a data file for problem 0450
'''

from __future__ import division        # new in 2.2, redundant in 3.0
from __future__ import absolute_import # new in 2.5, redundant in
2.7/3.0
from __future__ import print_function  # new in 2.6, redundant in 3.0

import io
import random

inFile = '0450.input.data'
#n, k, tiMax = 10**6, 3, 10**9
n, k, tiMax = 10**7, 3, 10**9

with io.open(inFile, 'wb') as f:
  f.write('%d %d\n' % (n, k))
  for i in xrange(n):
    ti = random.randint(1, tiMax)
    f.write('%d\n' % (ti,))


Steve