[Mesa-dev] [PATCH v3 5/5] loader/dri3: Enable adaptive sync via _VARIABLE_REFRESH property

[Kazlauskas, Nicholas]

On 10/11/2018 03:57 AM, Michel Dänzer wrote:
> On 2018-10-05 10:43 p.m., Nicholas Kazlauskas wrote:
>> The DDX driver can be notified of adaptive sync suitability by
>> flagging the application's window with the _VARIABLE_REFRESH property.
>>
>> This property is set on the first swap the application performs
>> when adaptive_sync_enable is set to true in the drirc.
>>
>> It's performed here instead of when the loader is initialized for
>> two reasons:
>>
>> (1) The window's drawable can be missing during loader init.
>>      This can be observed during the Unigine Superposition benchmark.
>>
>> (2) Adaptive sync will only be enabled closer to when the application
>>      actually begins rendering. For some displays this means there is
>>      less time spent watching flickering occur during application load.
>>
>> For now this property is only set on the glx DRI3 backend. This should
>> cover most common applications and games on modern hardware.
>>
>> Vulkan support can be implemented in a similar manner but would likely
>> require splitting the function out into a common helper function.
>>
>> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
>>
>> [...]
>>   
>> @@ -331,16 +360,25 @@ loader_dri3_drawable_init(xcb_connection_t *conn,
>>      draw->have_back = 0;
>>      draw->have_fake_front = 0;
>>      draw->first_init = true;
>> +   draw->adaptive_sync_enable = false;
>> +   draw->adaptive_sync_active = false;
>>   
>>      draw->cur_blit_source = -1;
>>      draw->back_format = __DRI_IMAGE_FORMAT_NONE;
>>      mtx_init(&draw->mtx, mtx_plain);
>>      cnd_init(&draw->event_cnd);
>>   
>> -   if (draw->ext->config)
>> +   if (draw->ext->config) {
>>         draw->ext->config->configQueryi(draw->dri_screen,
>>                                         "vblank_mode", &vblank_mode);
>>   
>> +      draw->ext->config->configQueryb(draw->dri_screen,
>> +                                      "adaptive_sync_enable",
>> +                                      &adaptive_sync_enable);
>> +
>> +      draw->adaptive_sync_enable = adaptive_sync_enable;
>> +   }
>> +
>>      switch (vblank_mode) {
>>      case DRI_CONF_VBLANK_NEVER:
>>      case DRI_CONF_VBLANK_DEF_INTERVAL_0:
>> @@ -879,6 +917,12 @@ loader_dri3_swap_buffers_msc(struct loader_dri3_drawable *draw,
>>      back = dri3_find_back_alloc(draw);
>>   
>>      mtx_lock(&draw->mtx);
>> +
>> +   if (draw->adaptive_sync_enable && !draw->adaptive_sync_active) {
>> +      set_adaptive_sync_property(draw->conn, (xcb_window_t)draw->drawable, true);
>> +      draw->adaptive_sync_active = true;
>> +   }
> 
> The window property should also either be deleted, or its value set to
> 0, when adaptive_sync_enable is false, to address the following scenario:
> 
> 1. Xorg is running without a compositor, and the user runs an OpenGL app
> which draws to the root window, e.g. an xscreensaver hack.
> 
> 2. Later, the user starts a compositor which draws to the root window.
> 
> Step one sets the window property to 1, so without the above, the
> compositor will use variable refresh even if it's blacklisted.
> 
> 

Good point. I'll go with setting the property to 0 only if the property
is already on the window so we don't end up adding it to windows that
don't need it.

Nicholas Kazlauskas