[Haskell-cafe] Using DPH

[Ben Lippmeier]

On 12/04/2011, at 11:50 PM, Wilfried Kirschenmann wrote:

> surprisingly, when removing the R.force from the code you attached,
> performances are better (speed-up=2). I suppose but I am not sure that
> this allow for loop fusions beetween the R.map ant the R.sum.
> 
> I use ghc 7.0.3, Repa 2.0.0.3 and LLVM 2.9.
> 
> By the end, the performances with this new version (0.48s) is 15x
> better than my original version (6.9s)
> However, the equivalent sequential C code is still 15x better (0.034s).
> 
> This may indeed be explained by the fact that all computations are
> performed inside the R.sum.

Yeah, the Repa fold and sum functions just use the equivalent Data.Vector ones. They're not parallelised and I haven't looked at the generated code. I'll add a ticket to the trac to fix these, but won't have time to work on it myself  in the near future.

Ben.