[Intel-gfx] [RFC] drm/i915: Scratch page optimization for blanking buffer

[Chris Wilson]

On Mon, May 05, 2014 at 05:13:18PM +0530, akash.goel at intel.com wrote:
> From: Akash Goel <akash.goel at intel.com>
> 
> There is a use case, when user space (display compositor) tries
> to directly flip a fb (without any prior rendering) on primary
> plane. So the backing pages of the object are allocated at page
> flip time only, which takes time. Since, this buffer is supposed to
> serve as a blanking buffer (black colored), we can setup all the GTT entries
> of that blanking buffer with scratch page (which is already zeroed out).
> This saves the time in allocation of real backing physical space for the
> blanking buffer and flushing of CPU cache.

So what happens with concurrent rendering via the GPU or GTT? And who
said that scratch was blank?

I wonder if there is a trivial operation in which you could grab the
pages and pull it into the mappable area prior to flipping.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre