[Mesa-dev] [PATCH 09/10] st/vdpau: implement the new DMA-buf based interop

[Marek Olšák]

On Wed, Sep 7, 2016 at 5:36 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Wed, Sep 7, 2016 at 4:08 AM, Michel Dänzer <michel at daenzer.net> wrote:
>> On 07/09/16 04:19 AM, Christian König wrote:
>>> Am 06.09.2016 um 21:05 schrieb Ilia Mirkin:
>>>> On Tue, Sep 6, 2016 at 2:22 PM, Christian König
>>>> <deathsimple at vodafone.de> wrote:
>>>>> Am 06.09.2016 um 16:23 schrieb Ilia Mirkin:
>>>>>> On Mon, Sep 5, 2016 at 2:48 AM, Michel Dänzer <michel at daenzer.net>
>>>>>> wrote:
>>>>>>> On 05/09/16 04:37 AM, Ilia Mirkin wrote:
>>>>>>>> On Tue, Mar 8, 2016 at 7:21 AM, Christian König
>>>>>>>> <deathsimple at vodafone.de> wrote:
>>>>>>>>> @@ -80,7 +82,7 @@ vlVdpOutputSurfaceCreate(VdpDevice device,
>>>>>>>>>       res_tmpl.depth0 = 1;
>>>>>>>>>       res_tmpl.array_size = 1;
>>>>>>>>>       res_tmpl.bind = PIPE_BIND_SAMPLER_VIEW |
>>>>>>>>> PIPE_BIND_RENDER_TARGET |
>>>>>>>>> -                   PIPE_BIND_LINEAR;
>>>>>>>>> +                   PIPE_BIND_LINEAR | PIPE_BIND_SHARED;
>>>>>>>> Hi Christian,
>>>>>>>>
>>>>>>>> This change appears to have semi-broken vdpau on nouveau. Whenever I
>>>>>>>> flip on the OSD in mplayer, the rendering becomes *extremely* slow.
>>>>>>>> However regular up-scaling without the OSD is plenty fast. This
>>>>>>>> effectively is forcing the output surfaces to live in GART instead of
>>>>>>>> VRAM.
>>>>>>> Strictly speaking, they'd only need to be forced to GART while they're
>>>>>>> actually being shared between different GPUs. That's how it works with
>>>>>>> the amdgpu and radeon kernel drivers.
>>>>>> Any suggestions on how to handle this? Perhaps reallocate + copy the
>>>>>> surface in st/vdpau when actual dmabuf sharing is requested?
>>>>>>
>>>>>> To be clear - with this change, vdpau with nouveau is unusable in the
>>>>>> presence of an OSD in mplayer. The OSD comes up whenever you seek
>>>>>> around in the video, so in effect, it's unusable. Used to work great.
>>>>>
>>>>> Well I think you should clearly figure out why adding
>>>>> PIPE_BIND_SHARED has
>>>>> such dramatic effect.
>>>> Because the buffer goes into GART. And then you try to blend on it,
>>>> which involves readback from GART (that's how the functions OSD is
>>>> based on work, I believe). We normally don't allocate renderable
>>>> surfaces or textures in GART.
>>>>
>>>>> We not only need this for DMA-buf based interop, but also for the
>>>>> DRI3 based
>>>>> sharing of buffers with X.
>>>>>
>>>>> So that clearly sounds like a bug in nouveau to me.
>>>> OK, so SHARED != GART? With nouveau, buffers are placed statically in
>>>> either VRAM or GART, so I think that if it's shared it has to end up
>>>> in GART, no?
>>>
>>> As far as I understand it no. Shared just means that we can share it
>>> between applications, doesn't it? Or does it mean the buffer should be
>>> shareable between GPUs?
>>>
>>> Could be that my understanding was wrong and so if it's the later feel
>>> free to provide a patch to just remove the flag.
>>>
>>>> I'm pretty weak on all these concepts, as well as how the DRI3 stuff
>>>> works, unfortunately.
>>>
>>> I have to confess I'm not so deeply into this stuff either. Marek,
>>> Michel what exactly is the meaning of the flag?
>>
>> According to src/gallium/docs/source/screen.rst:
>>
>> * ``PIPE_BIND_SHARED``: A sharable buffer that can be given to another
>>   process.
>>
>> It's also used e.g. for buffers shared via DRI3. So I'm afraid this is
>> something nouveau has to deal with better.
>
> Any suggestions that don't involve rewriting nouveau bo handling at
> every level (kernel, ddx, mesa)?
>
> Otherwise I'll send a revert for this change.

PIPE_BIND_SHARED means texture_get_handle is expected to be used on
the resource, meaning that inter-API, inter-process, or inter-device
sharing is possible. All window back buffers should have the flag. If
they don't, it's a bug. If the flag causes nouveau to put the buffer
in GART, it's a bug too. There is no reason to use GART for inter-API
and inter-process sharing like VDPAU and DRI3 are.

To be honest, the flag is pratically useless with respect to EGL and
VDPAU, which allow sharing almost any texture.

I suggest you fix nouveau. The first step would be to become less
dependent on BIND flags whose existence is already questionable.

Marek