From 31e9de9c8ac72399427cb0fc15f19205dd8182c9 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Michel=20D=C3=A4nzer?= Date: Fri, 2 Oct 2020 15:55:05 +0200 Subject: [PATCH] loader/dri3: Allocate up to 4 back buffers for page flips With swap interval 0, i.e. sync-to-vblank disabled. This can be necessary for unthrottled drawing with Xwayland: 1) One buffer can be scanned out 2) One buffer can be pending in the kernel for a page flip 3) One buffer can be pending in the Wayland compositor Therefore, with 3 buffers, the frame-rate could be capped much lower than the throughput the GPU is capable of, in the worst case at the Wayland compositor refresh rate. (The native Wayland EGL backend always uses up to 4 buffers) Leave the maximum number of buffers at 3 for swap interval != 0, it's sufficient in that case to always be able to queue one frame ahead of time. https://gitlab.gnome.org/GNOME/mutter/-/issues/1455 https://gitlab.gnome.org/GNOME/mutter/-/issues/1462 Cc: mesa-stable Reviewed-by: Eric Anholt Reviewed-by: Adam Jackson Part-of: --- src/loader/loader_dri3_helper.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-) diff --git a/src/loader/loader_dri3_helper.c b/src/loader/loader_dri3_helper.c index 1cb482d..82b8cba 100644 --- a/src/loader/loader_dri3_helper.c +++ b/src/loader/loader_dri3_helper.c @@ -275,10 +275,29 @@ static void dri3_update_max_num_back(struct loader_dri3_drawable *draw) { switch (draw->last_present_mode) { - case XCB_PRESENT_COMPLETE_MODE_FLIP: - /* Leave cur_num_back unchanged, it'll grow as needed */ - draw->max_num_back = 3; + case XCB_PRESENT_COMPLETE_MODE_FLIP: { + int new_max; + + if (draw->swap_interval == 0) + new_max = 4; + else + new_max = 3; + + assert(new_max <= LOADER_DRI3_MAX_BACK); + + if (new_max != draw->max_num_back) { + /* On transition from swap interval == 0 to != 0, start with two + * buffers again. Otherwise keep the current number of buffers. Either + * way, more will be allocated if needed. + */ + if (new_max < draw->max_num_back) + draw->cur_num_back = 2; + + draw->max_num_back = new_max; + } + break; + } case XCB_PRESENT_COMPLETE_MODE_SKIP: break; -- 2.7.4