From: Derek Foreman Date: Wed, 23 Nov 2016 22:40:42 +0000 (-0600) Subject: gbm/drm: Pick the oldest available buffer in get_back_bo X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=4f1d27a406478d405eac6f9894ccc46a80034adb;p=mesa.git gbm/drm: Pick the oldest available buffer in get_back_bo Applications may query the back buffer age to efficiently perform partial updates. Generally the application will keep a fixed length damage history, and use this to calculate what needs to be redrawn based on the age of the back buffer it's about to render to. If presented with a buffer that has an age greater than the length of the damage history, the application will likely have to completely repaint the buffer. Our current buffer selection strategy is to pick the first available buffer without considering its age. If an application frequently manages to fit within two buffers but occasionally requires a third, this extra buffer will almost always be old enough to fall outside of a reasonably long damage history, and require a full repaint. This patch changes the buffer selection behaviour to prefer the oldest available buffer. By selecting the oldest available buffer, the application will likely always be able to use its damage history, at a cost of having to perform slightly more work every frame. This is an improvement if the cost of a full repaint is heavy, and the surface damage between frames is relatively small. It should be noted that since we don't currently trim our queue in any way, an application that briefly needs a large number of buffers will continue to receive older buffers than it would if it only ever needed two buffers. Reviewed-by: Daniel Stone Signed-off-by: Derek Foreman Reviewed-by: Pekka Paalanen --- diff --git a/src/egl/drivers/dri2/platform_drm.c b/src/egl/drivers/dri2/platform_drm.c index 20993147c8a..f812ab543a6 100644 --- a/src/egl/drivers/dri2/platform_drm.c +++ b/src/egl/drivers/dri2/platform_drm.c @@ -215,13 +215,15 @@ get_back_bo(struct dri2_egl_surface *dri2_surf) struct dri2_egl_display *dri2_dpy = dri2_egl_display(dri2_surf->base.Resource.Display); struct gbm_dri_surface *surf = dri2_surf->gbm_surf; + int age = 0; unsigned i; if (dri2_surf->back == NULL) { for (i = 0; i < ARRAY_SIZE(dri2_surf->color_buffers); i++) { - if (!dri2_surf->color_buffers[i].locked) { + if (!dri2_surf->color_buffers[i].locked && + dri2_surf->color_buffers[i].age >= age) { dri2_surf->back = &dri2_surf->color_buffers[i]; - break; + age = dri2_surf->color_buffers[i].age; } } }