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

4 May 2016


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

Hong Yang