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

[Christian König]

Am 28.10.2016 um 19:37 schrieb Mario Kleiner:
>
>
> 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.

Yeah, that's pretty much what I had in mind as well. You additionally 
need to wait for the shared fences when you export the BO for the first 
time, but that's only a nitpick.

>
> 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?

Yes, exactly. VM updates doesn't matter for anybody else than amdgpu. 
Additional to that we don't even add a fence to the shared slot we 
reserve (could probably drop that for optimization).

Please remove the debugging stuff and the extra code on the VM updates 
and add a reservation_object_wait_timeout_rcu() to the export path and 
we should be good to go.

Regards,
Christian.

>
> All i can say is it fixes 3D rendering under DRI3 + Prime + 
> pageflipping without causing any obvious new problems.
>
> -mario