On Wed, Nov 19, 2008 at 4:17 PM, Simon Peyton-Jones <[EMAIL PROTECTED]> wrote: > | I'm compiling with -O2 -Wall. After looking at the Core output, I > | think I've found the key difference. A function that is bound in a > | "where" statement is different between the monolithic and split > | sources. I have no idea why, though. I'll experiment with a few > | different things to see if I can get this resolved. > > In general, splitting code across modules should not make programs less > efficient -- as Don says, GHC does quite aggressive cross-module inlining. > > There is one exception, though. If a non-exported non-recursive function is > called exactly once, then it is inlined *regardless of size*, because doing > so does not cause code duplication. But if it's exported and is large, then > its inlining is not exposed -- and even if it were it might not be inlined, > because doing so duplicates its code an unknown number of times. You can > change the threshold for (a) exposing and (b) using an inlining, with flags > -funfolding-creation-threshold and -funfolding-use-threshold respectively. > > If you find there's something else going on then I'm all ears. > > Simon >
I did finally find the changes that make a difference. I think it's safe to say that I have no idea what's actually going on, so I'll just report my results and let others try to figure it out. I tried upping the thresholds mentioned, up to -funfolding-creation-threshold 200 -funfolding-use-threshold 100. This didn't seem to make any performance difference (I didn't check the core output). This project is based on Oleg's Iteratee code; I started using his IterateeM.hs and Enumerator.hs files and added my own stuff to Enumerator.hs (thanks Oleg, great work as always). When I started cleaning up by moving my functions from Enumerator.hs to MyEnum.hs, my minimal test case increased from 19s to 43s. I've found two factors that contributed. When I was cleaning up, I also removed a bunch of unused functions from IterateeM.hs (some of the test functions and functions specific to his running example of HTTP encoding). When I added those functions back in, and added INLINE pragmas to the exported functions in MyEnum.hs, I got the performance back. In general I hadn't added export lists to the modules yet, so all functions should have been exported. So it seems that somehow the unused functions in IterateeM.hs are affecting how the functions I care about get implemented (or exported). I did not expect that. Next step for me is to see what happens if I INLINE the functions I'm exporting and remove the others, I suppose. Thank you Simon and Don for your advice, especially since I'm pretty far over my head at this point. John _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
