[Haskell] repa not running in parallel?

[Tikhon Jelvis]

I think you need to specify how many cores to use when you call your ./Main
program. Something like "./Main -random 4096 4096 -random 4096 4096 +RTS
-N4" (given that you have 4 cores). You'll also need to add -rtsopts when
you're compiling your code with ghc.


On Thu, Nov 7, 2013 at 1:40 AM, Alexander Herz <alexander.herz at mytum.de>wrote:

> Hi,
>
> I'm new to haskell and I tried to reproduce the perfomance values from the
> paper "Regular, Shape-polymorphic, Parallel Arrays in Haskell".
>
> I modified the repa-mmult example from the repa-example package to use the
> mmultP from Data.Array.Repa.Algorithms.Matrix.
>
> Then I compile it with "ghc -threaded -fglasgow-exts -O Main.hs" but
> running it with two large matrices :
>
> "./Main -random 4096 4096 -random 4096 4096" I can see that only one of my
> 4 cpus is utilized.
>
> What am I doing wrong?
>
> Note: The unmodified repa-example also does not run in parallel.
>
> Thx,
> Alex
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