[Haskell-cafe] Re: blas bindings, why are they so much slower the C?

[Don Stewart]

patperry:
> Last month Anatoly Yakovenko published some disturbing numbers about  
> the Haskell BLAS bindings I wrote being significantly slower than   
> using plain C.  I wanted to let everyone know that I've closed the  
> performance gap, and now for doing ten million dot products, the  
> overhead for using Haskell instead of C is about 0.6 seconds on my  
> machine, regardless of the size of the vectors.  The next version will  
> incorporate the changes.  If you can't wait for a formal release, the  
> darcs repository is at http://www-stat.stanford.edu/~patperry/code/blas/
> 
> Anyone interested in more details can check out my blog:
> http://quantile95.com/2008/07/24/addressing-haskell-blas-performance-issues/
> 
> Thanks everyone for the input on this (especially Anatoly).  If any  
> else finds any performance discrepancies, please let me know and I  
> will do whatever I can to fix them.
> 

Great work, Patrick!

So if I read correctly, the main change was to flatten the
representation (and thus in loops the vector's structure will be
unpacked and kept in registers, which isn't possible for sum types).

-- Don