Re: [PATCH] Revert "drm/i915: Kill GTT mappings when moving from GTT domain"

[Chris Wilson <chris@chris-wilson.co.uk>]

On Sun, 19 Jun 2011 10:01:23 -0700, Eric Anholt <eric@anholt.net> wrote:
> On Sun, 19 Jun 2011 17:28:11 +0100, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> > For lack of a better mechanism. Even using anholt/gtt-revert, I question
> > the value of caching the GTT mapping in drm_intel_bo. For the cairo-gl and
> > pts benchmarks I've run, the efficacy of the cached vma is very small and
> > there is a very slight improvement by unmapping the vma after use. (The
> > difference is so small, that it will take a lot more runs to determine if
> > it is statistically significant.)
> 
> I'm confused.  You've measured a 5% impact from removing this part of
> the caching, and I've measured 12-19%, so what are you planning that
> doesn't involve caching the mapping that's faster than caching the
> mapping?

As I pointed out, cairo-gl is using fallback code and not spans. Once that
is corrected, cairo-gl no longer continually recreating textures and so
unaffected by the patch. Removing the cached vma is then arguably
beneficial, though the difference looks to be in the noise.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre