[Intel-gfx] [PATCH] agp/intel, drm/i915: Use a write-combining map for updating PTEs

[Daniel Vetter]

On Sun, Aug 12, 2012 at 08:12:02PM +0100, Chris Wilson wrote:
> On Sun, 12 Aug 2012 17:01:08 +0100, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > On Sun, 12 Aug 2012 17:47:46 +0200, Daniel Vetter <daniel at ffwll.ch> wrote:
> > > On Sun, Aug 12, 2012 at 12:04:39PM +0100, Chris Wilson wrote:
> > > > In order to be able to ioremap_wc the GTT space, we need to remove the
> > > > conflicting pci_iomap from drm/i915, so we limit the register map in
> > > > drm/i915 to the suitable range for each generation. The benefit of doing
> > > > this is an order of magnitude reduction in time spent rewriting the GTT
> > > > entries when inserting and removing objects. For example, this halves the
> > > > CPU time spent in X when pushing pixels for chromium through a userptr
> > > > (chromium has a bug where it likes to recreate its ShmPixmap on every
> > > > draw).
> > > > 
> > > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > > 
> > > How well does this work with ums?
> > > 
> > > I guess if it blows up, we could ioremap uncached, but when kms
> > > initializes drop that uc mapping and try to remap wc. But I fear that ums
> > > will map the entire bar and hence we can't just unconditionally map the
> > > gatt wc.
> > 
> > It will work equisitely with ums. It will fail to do as it wishes and
> > fallback to VESA and everybody will be much happier...
> 
> So having rediscovered the hard truth that i915.modeset=1 and
> xf86-video-2.6.0 results in nasty hangs, setting the GTT table to WC has
> no effect upon the ancient UMS module - it shows the retro background
> and appears to function. We struck lucky. \o/

Ok, let's them the wrath of the abi gods. Merged to -queued, thanks for
the patch.
-Daniel
-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48