cairo performance is very bad

[guest]

I first generate 100,000 random lines. Drawing them with the cairo package takes 99 seconds. Drawing them with safe foreign imports takes 15 seconds. I haven't benchmarked unsafe foreign imports.

The 6.6x slowdown is rather high.

Benchmarking code attached. It might fail on systems where Double /= CDouble (a possible cause of the slowdown might be conversion between these).

[guest]

cairo performance benchmarking (random lines)

[guest]

Adding a link to the recent relevant discussion which indicates that float conversion suboptimality is probably to blame: http://www.haskell.org/pipermail/haskell-cafe/2011-November/096562.html

[dmwit]

Per the discussion on the mailing list, all the conversion functions are marked {-# INLINE #-} now.