Proton Experimental: Multiple games experience input lag / input event loss

Using latest Proton (probably started with experimental-wine-5.13-20210120 or experimental-wine-5.13-20210115), multiple games see input event loss or extreme lag.

Usually, single button presses on the gamepad aren't recognized, pressing it a second or third time and it works.

Sometimes, button presses are detected but the release isn't detected.

Axes sometimes do not update and just hang in some position until the situation eventually recovers after some time.

Button presses sometimes lag behind (usually just a short period, sometimes seconds). Axes also lag behind, often releasing an axis lags behind several seconds (see above).

In some games, this can also be observed for keyboard events. Mouse movement seems not to be affected but mouse buttons are. I usually do not play with mouse so I cannot really confirm this.

Games tested and affected:

• Borderlands 3
• Detroit: Become Human (this is very extreme)
• Control (by Remedy)

The problem is probably depending on CPU usage of the game, titles putting more pressure on the CPU experience the problem more intense. From a programmer perspective, I'd say that the scheduler is starving the input event threads in wine. This MAY be a result from using the MuQSS scheduler in my kernel but even if it is, this is a problem that should be fixed in wine as scheduler behavior tends to change over time or due to pressure put on the system.

No files, tests, or entry points are identified. Start by reproducing the input loss or lag in Borderlands 3, Detroit: Become Human, or Control under CPU load and trace the relevant Proton/Wine input path. Done would require affected gamepad or keyboard events to be delivered without loss or significant delay.