[RFC PATCH] XAA: Remove pluggable GC validation.

[Aaron Plattner]

On Tue, Jul 06, 2010 at 09:56:51AM -0700, Jamey Sharp wrote:
> This patch is part of a long series-in-progress, available here:
>         http://cgit.freedesktop.org/~jamey/xserver/log/?h=ops-rework
> I'm trying to reduce GC structures to only protocol-visible data plus
> privates, following a plan keithp suggested a few weeks ago. That plan
> has basically three goals:
>  - use callback chains where possible (e.g. resource destruction);
>  - replace the remaining wrappers with explicit linked lists;
>  - and move all GC-related function hooks from GC to ScreenRec.
> That requires not using ValidateGC to select GC ops.

This sounds bad.  GC ops are simple enough that every bit of validation
overhead causes significant performance regressions.  Pierre-Loup did an
experiment recently that showed that moving validation from ValidateGC to
the ops cost 5% on lines.