Joost Behrends wrote:
Neil Mitchell
writes: If it can be reproduced on anyones machine, it is a bug. If you can bundle up two programs which don't read from stdin (i.e. no getLine calls) or the standard arguments (i.e. getArgs) which differ only by the Data.Char import, and have massive speed difiference, then report a bug.
You should probably also give your GHC versions and platforms etc.
Thanks for your attention too !
Now i tried a version without input (just computing the primefactors of the constant 2^61+1, what it did correctly in spite of its bugginess). And it didn't have the Data.Char bug (and Data.List bug) too.
As my original code hasn't on Linux also it seems.
Thus it happens only in an exotic configuration. Windows will stay exotic in the Haskell community. Before should noone has reproduced it at least on Windows (XPpro SP2 is my version), i will do nothing more.
The hardware is Intel Celeron 2.2GHZ, 512 MB Ram. ghc 6.8.1 lives on D:\\Programme (not on the system drive C:, which poses problems to Cabal, told aside).
Even if it only happens on Windows, if it isn't specific to your hardware then it could still be a bug. I have seen strange artifacts like this before that turned out to be caused by one of two things: - bad cache interactions, e.g. we just happen to have laid out the code in such a way that frequently accessed code sequences push each other out of the cache, or the relative position of the heap and stack have a bad interaction. This happens less frequently these days with 4-way and 8-way associative caches on most CPUs. - alignment issues, such as storing or loading a lot of misaligned Doubles in the second case, I've seen the same program run +/- 50% in performance from run to run, just based on random alignment of the stack. But it's not likely to be the issue here, I'm guessing. If it is code misalignment, that's something we can easily fix (but I don't *think* we're doing anything wrong in that respect). I have an Opteron box here that regularly gives +/- 20% from run to run of the same program with no other load on the machine. I have no idea why... Cheers, Simon