Re: [PATCH] drm/i915: Skip fence installation for objects with rotated views (v2)

Chris Wilson
2015-10-27T18:47:27Z

On Tue, Oct 27, 2015 at 08:35:36PM +0200, Ville Syrjälä wrote:
> On Tue, Oct 27, 2015 at 06:03:52PM +0000, Chris Wilson wrote:
> > On Tue, Oct 27, 2015 at 02:26:55PM +0000, Tvrtko Ursulin wrote:
> > >
> > > On 27/10/15 13:48, Ville Syrjälä wrote:
> > > >On Tue, Oct 27, 2015 at 01:34:44PM +0000, Tvrtko Ursulin wrote:
> > > >>
> > > >>On 27/10/15 12:51, Ville Syrjälä wrote:
> > > >>>On Mon, Oct 26, 2015 at 06:23:26PM -0700, Vivek Kasireddy wrote:
> > > >>>>While pinning a fb object to the display plane, only install a fence
> > > >>>>if the object is using a normal view. This corresponds with the
> > > >>>>behavior found in i915_gem_object_do_pin() where the fencability
> > > >>>>criteria is determined only for objects with normal views.
> > > >>>>
> > > >>>>v2:
> > > >>>>Look at the object's map_and_fenceable flag to determine whether to
> > > >>>>install a fence or not (Chris).
> > > >>>>
> > > >>>>Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > > >>>>Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > > >>>>Cc: Daniel Vetter <daniel@ffwll.ch>
> > > >>>>Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> > > >>>>---
> > > >>>> drivers/gpu/drm/i915/intel_display.c | 3 ++-
> > > >>>> 1 file changed, 2 insertions(+), 1 deletion(-)
> > > >>>>
> > > >>>>diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > > >>>>index 52fb3f2..108c000 100644
> > > >>>>--- a/drivers/gpu/drm/i915/intel_display.c
> > > >>>>+++ b/drivers/gpu/drm/i915/intel_display.c
> > > >>>>@@ -2357,7 +2357,8 @@ intel_pin_and_fence_fb_obj(struct drm_plane *plane,
> > > >>>> * framebuffer compression. For simplicity, we always install
> > > >>>> * a fence as the cost is not that onerous.
> > > >>>> */
> > > >>>>- ret = i915_gem_object_get_fence(obj);
> > > >>>>+ if (obj->map_and_fenceable)
> > > >>>
> > > >>>This will now get the fence and pin it for the 90/270 view as well,
> > > >>>even though the fence doesn't even cover that particualr gtt mapping.
> > > >>
> > > >>I don't follow. obj->map_and_fenceable will be true only when normal
> > > >>view exists, so this avoids setting up the fence when no normal view
> > > >>exists and so avoids the WARN_ON in i915_gem_object_get_fence.
> > > >
> > > >Sure, but it's pointless to use up a fence if all we care about
> > > >is the 90/270 mapping.
> > >
> > > After a brief IRC discussion we agreed that the patch doesn't
> > > introduce any new negative behaviours.
> >
> > Urm, consider
> >
> > intel_unpin_fb_obj():
> > ...
> > i915_gem_object_unpin_fence(intel_fb_obj(obj));
>
> We'll have (pointlessly) pinned the fence too, so I think it'll end up
> working. I would have just put in view==NORMAL checks myself as an
> interim solution to avoid that, but whatever.

No, it didn't. If we rotated first, we don't get a fence and so don't
pin it. Then we attach an unrotated, grab a fence and pin it. Then we
end up unpinning twice vs a single pin.
-Chris

--
Chris Wilson, Intel Open Source Technology Centre