[Haskell-cafe] performance difference for binary-0.4.3.1 with ghc-6.8.3 and ghc-6.10

[Don Stewart]

jwlato:
> On Mon, Oct 27, 2008 at 12:34 AM, Alexander Dunlap
> <alexander.dunlap at gmail.com> wrote:
> > On Sun, Oct 26, 2008 at 9:36 AM, John Lato <jwlato at gmail.com> wrote:
> >> Hello,
> >>
> >> I was experimenting with using ghc-6.10.0.20081007 on a project, and
> >> it seems that binary-0.4.3.1 has markedly worse performance in certain
> >> cases.  With the following simple test:
> >>
> >>> import qualified Data.ByteString.Lazy as L
> >>> import Data.Binary
> >>> import Data.Binary.Get
> >>> import Control.Monad
> >>>
> >>> main :: IO ()
> >>> main = do
> >>>     b <- L.readFile "some_binary_file"
> >>>     putStrLn $ show $ runGet getter b
> >>
> >>> getter :: Get [Word16]
> >>> getter = replicateM 1000000 getWord16le
> >>
> >> running this program compiled with ghc-6.10 takes about 4 times as
> >> long (and consumes much more memory) as when compiled with ghc-6.8.3.
> >> The extra time appears to be proportional to the number of elements
> >> processed in the Get.  Running the programs with -hT shows a clear
> >> memory difference, which I think is the source of the problem.  I've
> >> placed pdfs of that output at https://webspace.utexas.edu/latojw/data/
> >>
> >> The difference seems to manifest itself only when the elements are
> >> actually processed; changing "show $ runGet " to "show $ length $
> >> runGet " is slightly faster in 6.10.
> >>
> >> I was working on an Intel Mac with OS 10.4, binary-0.4.3.1, and
> >> bytestring-0.9.1.4.  Can anyone confirm this, or suggest what might be
> >> the difference?
> >>
> >> Thank you,
> >> John Lato
> >> _______________________________________________
> >> Haskell-Cafe mailing list
> >> Haskell-Cafe at haskell.org
> >> http://www.haskell.org/mailman/listinfo/haskell-cafe
> >>
> >
> > With GHC 6.8.2:
> >
> > test: too few bytes. Failed reading at byte position 1613914
> >
> > real    0m27.573s
> > user    0m12.917s
> > sys     0m0.087s
> >
> > With GHC 6.11.20081003:
> >
> > test: too few bytes. Failed reading at byte position 1613914
> >
> > real    0m21.528s
> > user    0m14.759s
> > sys     0m0.135s
> >
> > I'm not using the exact same versions as you are, but I seem to be
> > getting different results.
> >
> 
> Hi Alexander,
> 
> Thanks for trying this out.  Based on your error, I'd guess that the
> file isn't large enough to read all the requested data.  In my case,
> it was about 70MB.  You could try reading from /dev/random, or rather
> than reading from a file, use something like
> 
> >> test_pure = let b = Data.ByteString.Lazy.repeat 1 in putStrLn $ show $ runGet getter b
> 
> I haven't tried a pure version myself, so I don't know what to expect
> from it.  Something to do tonight...
> 

I can reproduce the slowdown with ghc 6.10 in the binary benchmark
suite.  Investigating.

-- Don