[Haskell-cafe] To my boss: The code is cool, but it is about 100 times slower than the old one...

Clark Gaebel cgaebel at uwaterloo.ca
Thu Nov 29 20:17:35 CET 2012

If you can give an example of some underperforming code, I'm sure someone
(or several people) on this list would be more than happy to help you make
it more performant.

Generally, it doesn't take much. It's all in knowing where to look. Also,
if you know performance is key, you should be using the
performance-oriented data structures (ByteString, Text, Vector) from the
very beginning. Personally, I never find myself using Data.Array, and
rarely use String in real code. It's just not worth the performance

And finally, depending on what you're doing, neither Haskell, nor C might
be right for you! Especially with certain numerics-related code, you might
find fortran, OpenCL, or CUDA easier to make performant.

Examples of this would be lovely.

  - Clark

On Thu, Nov 29, 2012 at 2:00 PM, Alfredo Di Napoli <
alfredo.dinapoli at gmail.com> wrote:

> Hi there,
> I'm only an amateur so just my 2 cent: Haskell can be really fast, but
> reaching that speed can be all but trivial: you need to use different data
> types (e.g. ByteString vs. the normal String type) relies on
> "unconventional" IO (e.g. Conduit, Iterateee) and still be ready to go "out
> of the base", using packages and functions wich are not in base/haskell
> platform (e.g. mwc-random).
> My 2 cents :)
> A.
> On 29 November 2012 18:09, Fixie Fixie <fixie.fixie at rocketmail.com> wrote:
>> Hi all haskellers
>> I every now and then get the feeling that doing my job code in Haskell
>> would be a good idea.
>> I have tried a couple of times, but each time I seem to run into
>> performance problems - I do lots of heavy computing.
>> The problem seems to be connected to lazy loading, which makes my
>> programs so slow that I really can not show them to anyone. I have tried
>> all tricks in the books, like !, seq, non-lazy datatypes...
>> I was poking around to see if this had changed, then I ran into this
>> forum post:
>> http://stackoverflow.com/questions/9409634/is-indexing-of-data-vector-unboxed-mutable-mvector-really-this-slow
>> The last solution was a haskell program which was in the 3x range to C,
>> which I think is ok. This was in the days of ghc 7.0
>> I then tried compile the programs myself (ghc 7.4.1), but found that now
>> the C program now was more that 100x faster. The ghc code was compiled with
>> both O2 and O3, giving only small differences on my 64-bit Linux box.
>> So it seems something has changed - and even small examples are still not
>> safe when it comes to the lazy-monster. It reminds me of some code I read a
>> couple of years ago where one of the Simons actually fired off a new
>> thread, to make sure a variable was realized.
>> A sad thing, since I am More that willing to go for Haskell if proves to
>> be usable. If anyone can see what is wrong with the code (there are two
>> haskell versions on the page, I have tried the last and fastest one) it
>> would also be interesting.
>> What is your experience, dear haskellers? To me it seems this beautiful
>> language is useless without a better lazy/eager-analyzer.
>> Cheers,
>> Felix
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