On 2008 Aug 23, at 18:34, Krzysztof Skrzętnicki wrote:
Recently I wrote computation intensive program that could easily utilize both cores. However, there was overhead just from compiling with -threaded and making some forkIO's. Still, the overhead was not larger than 50% and with 4 cores I would probably still get the results faster - I didn't experience an order of magnitude slowdown. Perhaps it's the issue with OS X.
All that's needed for multicore to be a *lot* slower is doing it wrong. Make sure you're forcing the right things in the right places, or you could quietly be building up thunks on both cores that will cause lots of cross-core signaling or locking. And, well, make sure the generated code isn't stupid. Quite possibly the PPC code is an order of magnitude worse than the better-tested Intel code. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH