[Intel-gfx] [PATCH 1/3] drm/i915: Unbind the bo if the user requests a different alignment

[Chris Wilson]

On Mon, 12 Apr 2010 10:10:22 -0700, Eric Anholt <eric at anholt.net> wrote:
> On Sun,  4 Apr 2010 22:35:19 +0100, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > If the buffer is currently bound and does not meet the requested
> > alignment, then unbind it and repin.
> 
> Do we have any users legitimately requesting an alignment?  I thought
> they never existed or only lied when they did.

Yes, I invented one. ;-) Reusing surfaces within a batch with different
per-surface tiling parameters on pre-i965, without informing the kernel
that the buffer is tiled [so we can get away with reusing the surface
multiple times in the batch with different parameters...], and so having 
to manually request the minimal legal alignment for the relocated bo.
Given the transient nature of clip masks, glyph masks and intermediate
back buffers, we can reuse a lot of buffers within a single batch and
avoid catastrophic aperture thrashing.
-ickle

-- 
Chris Wilson, Intel Open Source Technology Centre