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

[Michel Dänzer]

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.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer