[Intel-gfx] [PATCH 05/14] drm/i915: kill ranged cpu read domain support

[Daniel Vetter]

On Thu, Feb 16, 2012 at 03:52:46PM -0800, Eric Anholt wrote:
> On Thu, 16 Feb 2012 18:38:08 +0100, Daniel Vetter <daniel at ffwll.ch> wrote:
> > On Thu, Feb 16, 2012 at 08:48:07AM -0800, Eric Anholt wrote:
> > > On Thu, 16 Feb 2012 13:11:31 +0100, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> > > > No longer needed.
> > > 
> > > What this code was for: Before gtt mapping, we were doing software
> > > fallbacks in Mesa with pread/write on pages at a time (or worse) of the
> > > framebuffer.  It would regularly result in hitting the same page again,
> > > since I was only caching the last page I'd pulled out, instead of
> > > keeping a whole copy of the framebuffer during the fallback.
> > 
> > Urgh, that's not really efficient ;-) I think for s/w fallbacks and
> > readbacks we can presume decent damage tracking (like sna does) on the
> > userspace sides.
> > 
> > > Since we've been doing gtt mapping for years at this point, I'm happy to
> > > see the code die.
> > > 
> > > I'm not sure about the rest of the code.  In particular, for the code
> > > that's switching between gtt and cpu mappings to handle a read/write,
> > > I'm concerned about whether the behavior matches for tiled objects.  I
> > > haven't reviewed enough to be sure.
> > 
> > Behaviour should match old code if you read/write entire pages (we should
> > have decent set of tests for that). If you do non-cacheline-aligned
> > reads/writes on tiled objects, we might hit an issue, but they should be
> > solveable (I've simply been too lazy to write testcases for this). Not
> > cacheline aligned reads/writes on untiled also work, I've created a set of
> > tests to exercise issues there (and tested the tests by omitting some of
> > the clflushes, i.e. all the clfushes now left _are_ required).
> > 
> > If old mesa depends on sub-page reads/writes to tiled objects I need to
> > create the respective tests and double-check the code, otherwise I think
> > we're covered. Do you want me to adapt the tests to check correctness for
> > sub-page reads/writes to tiled objects?
> 
> In the long long ago, I believe we did per-pixel accesses of tiled
> objects through pread/pwrite.  Crazy, I know.

Ok, I'll create a new tests to check partial, unaligned pwrites/preads on
tiled objects. On re-reading the patches the thing I'll likely got wrong
is that I don't swizzle the clflushing. But if we need to swizzle a page
we go through the slow-path anyway (no point in adding optimized code for
something no one cares about perf-wise anymore), so there shouldn't be any
issues with adding another branch to fix up the flushing. Won't be fast
though, but I guess no one cares ;-)

Cheers, Daniel
-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48