[PATCH] drm/i915: Before pageflip, also wait for shared dmabuf fences.

[Mike Lothian]

Hi Mario

That fixes the tearing, it's been replaced with a strange stutter, like
it's only showing half the number of frames being reported - it's really
noticeable in tomb raider

Thanks for your work on this, the stutter is much more manageable than the
tearing was

I've attached the patch that applies cleanly to 4.10-wip



On Fri, 28 Oct 2016 at 18:37 Mario Kleiner <mario.kleiner.de at gmail.com>
wrote:

>
>
> On 10/28/2016 03:34 AM, Michel Dänzer wrote:
> > On 27/10/16 10:33 PM, Mike Lothian wrote:
> >>
> >> Just another gentle ping to see where you are with this?
> >
> > I haven't got a chance to look into this any further.
> >
> >
>
> Fwiw., as a proof of concept, the attached experimental patch does work
> as tested on Intel HD Haswell + AMD R9 380 Tonga under amdgpu and
> DRI3/Present when applied to drm-next (updated from a few days ago).
> With DRI_PRIME=1 tearing for page-flipped fullscreen windows is gone
> under all loads. The tearing with "windowed" windows now looks as
> expected for regular tearing not related to Prime.
>
> ftrace confirms the i915 driver's pageflip function is waiting on the
> fence in reservation_object_wait_timeout_rcu() as it should.
>
> That entry->tv.shared needs to be set false for such buffers in
> amdgpu_bo_list_set() makes sense to me, as that is part of the buffer
> validation for command stream submission. There are other places in the
> driver where tv.shared is set, which i didn't check so far.
>
> I don't know which of these would need to be updated with a "exported
> bo" check as well, e.g., for video decoding or maybe gpu compute? Adding
> or removing the check to amdgpu_gem_va_update_vm(), e.g., made no
> difference. I assume that makes sense because that functions seems to
> deal with amdgpu internal vm page tables or page table entries for such
> a bo, not with something visible to external clients?
>
> All i can say is it fixes 3D rendering under DRI3 + Prime + pageflipping
> without causing any obvious new problems.
>
> -mario
>
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