Enormous FFI speedup observed

[Simon Marlow]

On 27/02/2012 10:46, Joachim Breitner wrote:
> Hi,
>
> as I wrote on
> http://www.joachim-breitner.de/blog/archives/546-GHC-7.4.1-speeds-up-arbtt-by-a-factor-of-22.html
> I observe an enormous speed up (22×) in arbtt, and it seems to be
> related to FFI function calls. The release notes do not give a hint what
> has changed to result in this speed up, so I’m curious whether someone
> here knows the reason, or can make a good guess?

A couple of guesses:

Avoiding slop in pinned objects:
http://hackage.haskell.org/trac/ghc/changeset/cc2ea98ac4a15e40a15e89de9e47f33e191ba393

Stack chunks:
http://hackage.haskell.org/trac/ghc/changeset/f30d527344db528618f64a25250a3be557d9f287


but it's hard to know for sure without investigating more closely.

Cheers,
	Simon