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

[Baojun Wang]

ByteString Builder is supposed to build bytestring incrementally (as
monoid), in the example it prints the builder immediately after build a
single ``char7'', thus not necessary to use bytestring builder at all
(which introduces overhead).

On Wed, May 4, 2016 at 7:21 PM Hong Yang <hyangfji at gmail.com> wrote:

> 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?
>> >> >
>> >> >
>> >> > _______________________________________________
>> >> > Haskell-Cafe mailing list
>> >> > Haskell-Cafe at haskell.org
>> >> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> >> >
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe at haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>>
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20160505/11724925/attachment.html>