cross module optimization issues

[Mitchell, Neil]

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 at haskell.org 
> [mailto:glasgow-haskell-users-bounces at haskell.org] On Behalf 
> Of Simon Peyton-Jones
> Sent: 21 November 2008 10:34 am
> To: John Lato
> Cc: glasgow-haskell-users at 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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