Recently news went around about explicit sync being merged into Wayland protocols, and in the wake of that I saw a lot of people having questions about it, and why it was such a big deal… So here’s a short-ish explanation of what it is, why it’s needed and what the benefits are over the old model.

tl;dr this Wayland protocol will implement explicit sync in a standardised way which means better Wayland performance and compatibility with Nvidia cards in particular

If we already have “explicit sync through a backdoor”, and explicit sync doesn’t bring major performance improvements for everyone, why is it such big news then?

The answer is simple: The proprietary NVidia driver doesn’t support implicit sync at all, and neither commonly used compositors nor the NVidia driver support the first explicit sync protocol, which means on Wayland you get significant flickering and frame pacing issues. The driver also ships with some workarounds, but they don’t exactly fix the problem either:

  • it delays Wayland commits until rendering is completed, but it goes against how graphics APIs work on Wayland and can cause serious issues, even crash apps in extreme cases
  • it delays X11 presentation until rendering is completed, but as Xwayland copies window contents sometimes, that still often causes glitches if Xwayland is also using the NVidia GPU for those copies