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

[John Lato]

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
>> _______________________________________________
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>> 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...

Cheers,
John