[Intel-gfx] [PATCH 07/18] drm/i915: Defer allocation of stolen memory for FBC until actual first use

[Chris Wilson]

On Mon, 5 Nov 2012 15:00:36 +0000, Ben Widawsky <ben at bwidawsk.net> wrote:
> On Fri, 19 Oct 2012 18:03:13 +0100
> Chris Wilson <chris at chris-wilson.co.uk> wrote:
> 
> > As FBC is commonly disabled due to limitations of the chipset upon
> > output configurations, on many systems FBC is never enabled. For those
> > systems, it is advantageous to make use of the stolen memory for other
> > objects and so we defer allocation of the FBC chunk until we actually
> > require it. This increases the likelihood of that allocation failing,
> > which in turns means that we are already taking advantage of the stolen
> > memory!
> 
> I'm failing to see how this patch is doing what it advertises to do. At
> least applies to dinq it's only deferring the error check. None of the
> steps that now happen before allocating the stolen compressed fb use
> stolen memory. On any of the errors, we seem to free the stolen memory.
> I see a mode check, a platform/plane check, a tiling check, a debug
> check now happening before we setup compression, but I fail to see how
> that really effects anything.... I'm sorry if I am being obtuse, but
> could you please explain a bit better?

All of those previous checks are more likely to be false - and
previously we never tried to recover the stolen memory. I can go back to
a single patch as this is now just an optimisation rather than
preventing a permanent loss of memory.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre