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

[Christian König]

Am 07.09.2016 um 18:06 schrieb 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.

Actually I can think of a very good use case for the kernel where I 
could reduce the per command submission / per BO handle overhead 
significantly if we could mark BOs which are never shared between 
applications as such.

Christian.

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