[Haskell-cafe] Using loop fusion for writing efficent high-level code Re[2]: [Haskell] [Fwd: Re: Computer Language Shootout]

Duncan Coutts duncan.coutts at worc.ox.ac.uk
Wed Feb 28 18:56:16 EST 2007

On Wed, 2007-02-28 at 09:51 -0800, Bryan O'Sullivan wrote:
> Bulat Ziganshin wrote:
> > can you please provide examples of such code?
> I'd recommend taking a look at the new binary package.  It's very 
> cleanly written, and mostly easy to understand.  It's also easy to see 
> where the optimisations have been made.  The only part that might induce 
> sudden cranial expansion is the Builder monoid, which constructs a big 
> delayed computation to efficiently fill out a lazy ByteString when the 
> Put monad is run.
> The optimisations haven't perverted the readability of the code much, 
> but it's still quite fast.  I've clocked end-to-end serialisation and 
> deserialisation over an Infiniband network at 234 MB/sec (~25% of line 
> rate).  This consumed about 90% of one CPU on the sending side, while 
> the receiving side was 100% pegged.

Yes, we've optimised the writing side much more than the reading side at
the moment. I'm sure it's possible to get the reading up to at least the
same speed. I think we ought to be able to push both further after that
because we're still not doing the bounds check commoning up
transformation that we'd planned on (more GHC rules). So given enough
hacking time there's more performance available.

In our benchmarks reading is currently about 40% of writing speed and
we're topping out at about 30-40% of maximum memory bandwidth for
writes. Apparently that's only 200x faster than the faster of two common
python serialisation libs, so we've got some way to go yet.


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