[Intel-gfx] [PATCH 15/16] drm/i915: Wa32bitGeneralStateOffset & Wa32bitInstructionBaseOffset

[Chris Wilson]

On Tue, May 26, 2015 at 05:25:48PM +0200, Daniel Vetter wrote:
> On Tue, May 26, 2015 at 03:21:22PM +0100, Michel Thierry wrote:
> > There are some allocations that must be only referenced by 32bit
> > offsets.

> > To limit the chances of having the first 4GB already full,
> > objects not requiring this workaround don't use the first 2 PDPs.

This is complete tosh. Please have a later patch that uses SEARCH_BELOW
for 48bit objects, and cite eviction rates and improvements.

> This is the wrong way round for existing userspace (and remember, bdw is
> shipping already so we can't opt out of that). Instead the w/a needs to
> allow 32bit+ addresses only if the new bit is set.
> 
> Also this needs the usual pile of userspace enabling (libdrm+mesa).

Indeed, the code is very much broken as is. So I expect to see a
Testcase: igt/gem_exec_48bit in the next patch.

As a hint, consider reusing the object.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre