On 15/12/09 00:37, Philip Beadling wrote:
If you still have trouble, then try using ThreadScope
http://code.haskell.org/ThreadScope/
with GHC 6.12.1. You can use ThreadScope directly from the darcs repository on code.haskell.org, and we hope to do a proper release soon.
Cheers, Simon
Thanks for the advice, just downloaded ThreadScope and it's pretty useful (before I was using Ubuntu's System Monitor which isn't ideal).
I've moved onto 6.12 and I now have my program working nicely over 2 cores - the problem was at least in part my own design - I was generating large thunks in my parallel version which was killing performance. With this solved 2 cores gives me ~50% performance increase.
What I'm doing now is taking a list I am going to fold over and splitting it up so I have a list of lists, where each parent list element representing work for 1 core. I then fold lazily and only parallelise on the final sum operation which (as far as I can see) sends each chunk of folds to a different core and sums the results.
Can I confirm - what you are suggesting is that although I can't parallelise fold itself, I could force evaluation on the list I am about to fold in parallel and then merely accumulate the result at the end -- thus most the donkey work is done in parallel?
Yes. If it turns out that the list elements are too small to spark individually, then you may want to split the list into chunks and evaluate/sum the chunks in parallel, before summing the result. This is a typical map/reduce pattern. Cheers, Simon