Composite redraw speedup?

[Michel Dänzer]

On 2020-02-12 2:06 p.m., Carsten Haitzler wrote:
> On Wed, 12 Feb 2020 13:23:28 +0200 Pekka Paalanen <ppaalanen at gmail.com> said:
> 
>> On Wed, 12 Feb 2020 11:07:56 +0000
>> Carsten Haitzler <raster at rasterman.com> wrote:
>>
>>> On Wed, 12 Feb 2020 12:40:15 +0200 Pekka Paalanen <ppaalanen at gmail.com>
>>> said:
>>>
>>>> On Wed, 12 Feb 2020 10:21:02 +0000
>>>> Carsten Haitzler (The Rasterman) <raster at rasterman.com> wrote:
>>>>   
>>>>> even better - if the /dev/dri/card0
>>>>> device exists, dlopen libdrm and get some symbols from it and ... use
>>>>> it to request the drm device sent you vsync events so you can use the
>>>>> vsync interrupt as your frame event. this will be another fd to listen
>>>>> on in select() and of course you can turn this vblank event stream on
>>>>> and off.  
>>>>
>>>> Please don't. Talk to the X server instead.  
>>>
>>> and what vsync events does the xserver provide? 
>>
>> You don't want vsync events. You have no idea what they
>> correspond to, or even if you opened the right device.
>>
>> https://gitlab.freedesktop.org/xorg/proto/xorgproto/blob/master/presentproto.txt
> 
> I wrote the drm support before the present extension existed. The drm
> path is  easy to support - only open if a single card exists (if multiple -
> don't do it and fall back to timer based animation) and you can filter for
> multiple screens as you get events for all screens. Yes - you end up syncing
> with a single chosen screen if you filter for just one of the vblank events,
> but it's better than using the system clock.

You only get an event for the CRTC you ask for in the
DRM_IOCTL_WAIT_VBLANK ioctl. How do yo know which CRTC to pick?


> I have found x present XPresentNotifyMSC() to be unreliable where the
> drm back-door above is far more reliable. For example - on my amdgpu driver
> here it just refuses to produce any events (yes - extension is there), [...]

I haven't seen any such reports, so I'm not aware of such issues with
xf86-video-amdgpu.


-- 
Earthling Michel Dänzer               |               https://redhat.com
Libre software enthusiast             |             Mesa and X developer