[Intel-gfx] xf86-video-intel: src/xvmc/intel_xvmc.c

[Barry Scott]

Zou, Nanhai wrote:
>> -----Original Message-----
>> From: Wang, Zhenyu Z
>> Sent: 2008年12月18日 16:07
>> To: Zou, Nanhai
>> Cc: intel-gfx
>> Subject: Re: xf86-video-intel: src/xvmc/intel_xvmc.c
>>
>> On 2008.12.17 13:55:41 +0800, Nan hai Zou wrote:
>>     
>>>  src/xvmc/intel_xvmc.c |    2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> New commits:
>>> commit 555eea5411cf8c725df5f1b4cb80198fa6a1225b
>>> Author: Zou Nan hai <nanhai.zou at intel.com>
>>> Date:   Wed Dec 17 13:55:07 2008 +0800
>>>
>>>      wait vblank before render to fix tearing
>>>
>>> diff --git a/src/xvmc/intel_xvmc.c b/src/xvmc/intel_xvmc.c
>>> index dbde22f..c197e35 100644
>>> --- a/src/xvmc/intel_xvmc.c
>>> +++ b/src/xvmc/intel_xvmc.c
>>> @@ -757,7 +757,7 @@ _X_EXPORT Status XvMCPutSurface(Display
>>>       
>> *display,XvMCSurface *surface,
>>     
>>>      }
>>>      intel_surf->last_draw = draw;
>>>      /* fill intel_surf->data */
>>> -    if (0)
>>> +    if (1)
>>>      {
>>>  	drmVBlank vbl;
>>>  	vbl.request.type = DRM_VBLANK_RELATIVE;
>>>       
>> This is broken as no care is taken for vblank pipes (e.g I have to
>> add DRM_VBLANK_SECONDARY for my GM965 LVDS on pipe B).
>> As XvMC uses Xv port for video playback, we should just fix
>> Xv port for vblank sync. My suggest is to add a Xv port attribute
>> for texture video, that can flip vblank wait on or off. Or we
>> might steal some idea from radeon driver. But doing this in XvMC
>> lib is wrong to me anyway.
>>
>>     
> Wait in server context is not a good idea, either busy wait or sleep, user experience will not be good when server stall for vblank.
> So let's do it in client context.
>   

I agree in principle. But we found that only one app on a host can wait
for VBLANK. If, for example OpenGL has the vblank
when you try for it in XvMC VBLANK will be delivered late and cause tearing.

In our application we had to ensure only one process waited for VBLANK
and then use futext to send a pulse to all our
other apps that need to be in sync with VBLANK.

We believe that you will need to fix DRM for intel to allow multiple
clients to wait for VBLANK if you wish to make this work.
There is code in DRM that changes notification delivery based on the
number of clients waiting. When there is 1 it works
great, 2 or more it delivers about ~10ms late. (We see a tear between
1/3 and 2/3 down the screen).

Barry