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st/dri: decrease input lag by syncing sooner in SwapBuffers

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It's done by:
- decrease the number of frames in flight by 1
- flush before throttling in SwapBuffers
  (instead of wait-then-flush, do flush-then-wait)

The improvement is apparent with Unigine Heaven.

Previously:
    draw frame 2
    wait frame 0
    flush frame 2
    present frame 2

    The input lag is 2 frames.

Now:
    draw frame 2
    flush frame 2
    wait frame 1
    present frame 2

    The input lag is 1 frame. Flushing is done before waiting, because
    otherwise the device would be idle after waiting.

Nine is affected because it also uses the pipe cap.
This commit is contained in:
Marek Olšák 2019-04-22 17:11:00 -04:00
parent d30ce03bc0
commit 20909284f2
2 changed files with 11 additions and 11 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
src/gallium/auxiliary/util/u_screen.c
View file

@ -356,7 +356,7 @@ u_pipe_screen_get_param_defaults(struct pipe_screen *pscreen,
return 0;
case PIPE_CAP_MAX_FRAMES_IN_FLIGHT:
return 2;
return 1;
case PIPE_CAP_DMABUF:
#ifdef PIPE_OS_LINUX

20
src/gallium/state_trackers/dri/dri_drawable.c
View file

@ -562,19 +562,19 @@ dri_flush(__DRIcontext *cPriv,
* flush method returns a fence even if there are no commands to flush.
*/
struct pipe_screen *screen = drawable->screen->base.screen;
struct pipe_fence_handle *fence;
struct pipe_fence_handle *oldest_fence, *new_fence = NULL;
fence = swap_fences_pop_front(drawable);
if (fence) {
(void) screen->fence_finish(screen, NULL, fence, PIPE_TIMEOUT_INFINITE);
screen->fence_reference(screen, &fence, NULL);
st->flush(st, flush_flags, &new_fence);
oldest_fence = swap_fences_pop_front(drawable);
if (oldest_fence) {
screen->fence_finish(screen, NULL, oldest_fence, PIPE_TIMEOUT_INFINITE);
screen->fence_reference(screen, &oldest_fence, NULL);
}
st->flush(st, flush_flags, &fence);
if (fence) {
swap_fences_push_back(drawable, fence);
screen->fence_reference(screen, &fence, NULL);
if (new_fence) {
swap_fences_push_back(drawable, new_fence);
screen->fence_reference(screen, &new_fence, NULL);
}
}
else if (flags & (__DRI2_FLUSH_DRAWABLE | __DRI2_FLUSH_CONTEXT)) {