Hi John, I'm vaguely curious, and have next week off, so if you can provide the code, and directions for running in both variants and the test case, I'll take a look. Please email me at ndmitchell -AT- gmail.com though, as I loose this email address at 11pm tonight :-) Thanks Neil
-----Original Message----- From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users-bounces@haskell.org] On Behalf Of Simon Peyton-Jones Sent: 21 November 2008 10:34 am To: John Lato Cc: glasgow-haskell-users@haskell.org; Don Stewart Subject: RE: cross module optimization issues
| 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.
I'm totally snowed under with backlog from my recent absence, so I can't look at this myself, but if anyone else wants to I'd be happy to support with advice and suggestions.
In general, having an explicit export list is good for performance. I typed an extra section in the GHC performance resource http://haskell.org/haskellwiki/Performance/GHC to explain why. In general that page is where we should document user advice for performance in GHC.
I can't explain why *adding* unused functions would change performance though!
Simon
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