[Intel-gfx] [PATCH] drm/i915: Unconditionally flush writes before execbuffer

[Chris Wilson]

On Mon, May 11, 2015 at 04:25:52PM +0100, Chris Wilson wrote:
> On Mon, May 11, 2015 at 12:34:37PM +0200, Daniel Vetter wrote:
> > On Mon, May 11, 2015 at 08:51:36AM +0100, Chris Wilson wrote:
> > > With the advent of mmap(wc), we have a path to write directly into
> > > active GPU buffers. When combined with async updates (i.e. avoiding the
> > > explicit domain management along with the memory barriers and GPU
> > > stalls) we start to see the GPU read the wrong values from memory - i.e.
> > > we have insufficient memory barriers along the execbuffer path. Writes
> > > through the GTT should have been naturally serialised with execution
> > > through the GTT as well and so the impact only seems to be from the WC
> > > paths.
> > > 
> > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > > Cc: Akash Goel <akash.goel at intel.com>
> > > Cc: stable at vger.kernel.org
> > 
> > Do we have a nasty igt for this? Bugzilla?
> 
> I've added igt/gem_streaming_writes.

So far the only thing that makes a difference on !llc is hitting it with
wbinvd().

I wonder if EXEC_OBJECT_WBINVD (or EXEC_OBJECT_WMB to be less specific)
is acceptable?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre