Composite redraw speedup?

[Michel Dänzer]

On 2020-02-12 6:42 p.m., Carsten Haitzler wrote:
> On Wed, 12 Feb 2020 16:45:50 +0100 Michel Dänzer <michel at daenzer.net> said:
> 
>> On 2020-02-12 4:34 p.m., Carsten Haitzler wrote:
>>> On Wed, 12 Feb 2020 15:36:06 +0100 Michel Dänzer <michel at daenzer.net> said:
>>>
>>>> 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?
>>>
>>> drmVBlank vbl;
>>> vbl.request.type = DRM_VBLANK_RELATIVE | DRM_VBLANK_EVENT;
>>> vbl.request.sequence = 1;
>>> vbl.request.signal = 0;
>>> drmWaitVBlank(drm_fd, &vbl);
>>>
>>> has worked a charm for maybe give or take close to a decade (as i said -
>>> before present existed).
>>
>> That selects the first CRTC. It'll work most of the time, except when
>> the first CRTC isn't enabled for some reason.
> 
> I've seen it select multiple crtc's as I get multiple vblank events with the
> same frame number... (thus filter out the dups to only get one).

Sounds like something's wrong.

Try setting vbl.request.signal to a unique (e.g. monotonically
increasing) value for each drmWaitVBlank call. The value is replicated
in the user_data field of the corresponding event. If you get multiple
events with the same user_data value, that indicates a kernel bug.


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