[Haskell-cafe] ghc-prof-options and libraries on Hackage

[Oliver Charles]

Hi all,

I'd like to start a conversation around the ghc-prof-options option that
can be used in Cabal-ized libraries. As you may know, this option specifies
extra GHC options that are used when --enable-library-profiling is enabled.
This is very convenient for local development, but I argue that it can be
counter-productive for releases onto Hackage.

To provide an example, I'm currently working on a little game engine that
uses JuicyPixels to load images. I have a problem in my code that needs
optimizing, but the current state of things results in profiles that are
very difficult to work with. JuicyPixels specifies -auto-all in its cabal
file, which means I have no alternative but to profile JuicyPixels code. In
this scenario, the bottleneck is actually within my FRP game loop and
nothing to do with image loading! As a result, the profiles are fairly
useless to me.


Roman Cheplyaka also points out that by doing this, profiles are skewed -
-auto-all is not free, so we actually pay in runtime performance every time
a library does this.

I would like to hear from others if we should consider managing this option
a little more. My personal feeling is that this flag shouldn't be used
unless in local development, so guarded by an off-by-default build flag. I
think cabal should also warn authors who are using this flag, and encourage
them to place a guard around this option.

Thoughts?
- ocharles
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