Hello John, Thursday, November 5, 2009, 1:59:14 PM, you wrote:
I hope you don't mind me asking this, but when you state that "idiomatic haskell is much slower than idiomatic C", what do you mean by "much slower"? 2 times? 3 times? 20 times? Order of magnitude?
it depends on task, of course. with a number crunching code, it may be hundreds or even thousands, but this application area isn't typical for haskell, after all. for typical apps like text processing it may be dozens. when we are going into real life, use of FFI libraries and OS calls makes difference even smaller, so i think that practical difference is 3-10 times, in most cases
I'm not going to disagree with you, however it seems to me the gap is closing.
except for BS library, i don't see too much practical improvements. GHC by itself was made ~20% faster with pointer tagging
My opinion may be colored by having just examined Masayuki Takagi's SPH code, which I considered very idiomatic Haskell and for me performed equivalently to his C++ code with the changes I detailed in an earlier email (none of which involved any substantial changes to his code or style in my opinion).
i don't know why his haskell code is so fast - it may be due to improvements in ghc about compiling tight loops, unoptimal C code, bounds placed by memory speed. well, i know one problem in his C compilation - he doesn't used -O3 -fexcess-precision and other funny optimization tricks there is difference in treating good and bad comparisons. when someone shows that haskell is much slower, there are lot of suggestions how to improve the code, add strictness, use other libs, apply tricky compiling options, even unroll loops by hand. when someone shows small gap between C and Haskell, noone checks that C code is optimized as much as possible. of course, it's mainly because many haskellers can't optimize C code. but this should lead to the conclusion "i'm incompetent in comparison" rather than "haskell is fast"
Best, John
From: Bulat Ziganshin
i don't say that haskell is slow for real programs. i say that idiomatic haskell is much slower than idiomatic C and these papers demonstrates how much, for simple computation-intensive loops
-- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com
-- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com