Mesa Lands Option That Can Help XWayland-Based Gaming On The Steam Deck

Mesa 21.3 today landed a debug option that can help with the XWayland-based gaming performance around latency and for power management as well.

Via the vk_xwayland_wait_ready=false DRIConf option, Mesa's Vulkan windowing system integration code will wait less. Currently the Mesa Vulkan WSI code with XWayland will wait for buffers to be ready before they are submitted to XWayland when operating in Vulkan's "immediate" mode. But for some Wayland compositors that default behavior is undesirable.

This change was proposed three months ago to alter the default behavior of the Vulkan X11 WSI code but with it regressing things for some Wayland compositors, the decision was made to make it a DRIConf option so users can opt-in to avoiding the wait around fences.

Simon Ser who proposed this change noted their motivation with this option to not wait under XWayland was done in the name of power management for better balancing between the CPU/GPU for battery-powered devices.

Valve's Pierre-Loup Griffais commented as well and was the motivating factor in moving this from a default behavior change to just an option, "Even without the power management aspect (which is quite important), this model would prevent effective pipelining of the composition step behind the app's buffer and would always result in a CPU bubble reliant on just-in-time scheduling - we're not really interested in leaving perf, latency or functionality on the table because of limitations of other compositors / platforms, so could we just cut this discussion short and make that a tunable setting instead of arguing about usecases? The alternative would be for us to have a ship a downstream patched tree, which would be quite annoying."

Given that commentary, they are very interested in the change for Valve's forthcoming Steam Deck for improving the XWayland-based gaming experience.

That change is now merged for Mesa 21.3.