[Haskell-cafe] Is Haskell IO inherently slower than C?

[Hong Yang]

I never used Data.ByteString.Builder before. But I guess "char7" is
encoding a space to something. Will this slow things down?

On Wed, May 4, 2016 at 8:44 PM, Mike Izbicki <mike at izbicki.me> wrote:

> That convinces me that your Haskell program is actually slower.  My
> guess is this is due to a buffering issue, and not due to anything
> haskell related.  Buffering is how the opeating system makes a
> tradeoff between performance and safety for io operations, and I'm
> guessing your two code fragments are (behind the scenes) making a
> different decision about how to do buffering.
>
> For a Haskell-related discussion about buffering, see:
> http://book.realworldhaskell.org/read/io.html#io.buffering
>
> BTW, a good rule of thumb for io performance in any language is to
> never write anything character by character, and instead write large
> chunks of characters at once.  The above link should make clear why
> this is the case.
>
> On Wed, May 4, 2016 at 6:22 PM, Jake <jake.waksbaum at gmail.com> wrote:
> > Thanks for the tip! I tried it again, this time using 100000000, and the
> > Haskell one runs at around 25 seconds. The C one is only 1.5 seconds. Can
> > that still be the run time system?
> >
> > On Wed, May 4, 2016 at 9:18 PM Mike Izbicki <mike at izbicki.me> wrote:
> >>
> >> You need to be doing tests that take much longer to accurately compare
> >> runtimes of executables.  Here's why:
> >>
> >> Haskell programs have a more complicated run time system than C
> >> programs, and the binaries output by GHC are much larger.  Therefore,
> >> there will be a small additional overhead that you have to pay once
> >> when the program starts.  For some machines, this could possibly be on
> >> the order of 0.3 seconds.
> >>
> >> I'd recommend you scale your test so that it takes at least 30 seconds
> >> for the slowest program.  This will give you more meaningful results.
> >>
> >> On Wed, May 4, 2016 at 6:07 PM, Jake <jake.waksbaum at gmail.com> wrote:
> >> > I also tried the more standard forM_ [0..100000] idiom and got similar
> >> > times. I hoped loop might be faster, but apparently not.
> >> >
> >> > On Wed, May 4, 2016 at 9:05 PM Jake <jake.waksbaum at gmail.com> wrote:
> >> >>
> >> >> I'm trying to write a program in Haskell that writes a large file at
> >> >> the
> >> >> end, and it seems like that output alone is taking way longer than it
> >> >> should. I don't understand why Haskell shouldn't be able to write
> data
> >> >> as
> >> >> quickly as C, so I wrote two test files:
> >> >>
> >> >> -- Test.hs
> >> >> import Control.Loop
> >> >> import Data.ByteString.Builder
> >> >> import System.IO
> >> >>
> >> >> main :: IO ()
> >> >> main =
> >> >>   numLoop 0 1000000 $ \_ ->
> >> >>     hPutBuilder stdout $ char7 ' '
> >> >>
> >> >> // test.c
> >> >> #include <stdio.h>
> >> >>
> >> >> int main() {
> >> >>   int i;
> >> >>   for (i = 0; i < 1000000; i++) {
> >> >>     fprintf(stdout, " ");
> >> >>   }
> >> >>   return 0;
> >> >> }
> >> >>
> >> >> I compiled them both with -O2, and ran them redirecting their outputs
> >> >> to
> >> >> /dev/null. For the Haskell version I got times aroudn 0.3 seconds,
> >> >> while the
> >> >> C version was around 0.03. Is there any reason why in simple IO the
> >> >> Haskell
> >> >> version would be slower by an order of magnitude?
> >> >
> >> >
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> >> >
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