Xorg 1.20 Mouse Cursor Lag

[apokalypz]

My platform: Chromebook Plus (RK3399 chipset) running aarch64. Xorg drivers: Modesetting (no acceleration), xf86-input-libinput.

Problem: When running GIMP, I noticed very severe mouse lag while having a part of my image selected. I noticed the lag occurs in step with the "marching ants" around the selected portion of the image. This tells me the Xorg dirty screen writes are blocking the mouse from updating. I noticed this issue right after I updated to Xorg 1.20 and rebooted.

Troubleshooting: I looked through my Xorg log and noticed that "SilkenMouse" was disabled (I remembered it used to be enabled prior to 1.20). Looking at the documentation for SilkenMouse, I learned that it was implemented to handle mouse events separately from graphics updates to prevent the exact issue I'm having. The strange thing is, I searched the interwebs for more information and noticed that most people that run Xorg 1.20 have SilkenMouse Disabled in their logs as well, where as most logs prior to 1.20 have it enabled. This leads me to believe it might not just be me having this issue. So I downloaded the pkgbuild and friends from the arch repository, looked where it enabled SilkenMouse and noticed it depends on InputThreadEnable being true...which it isn't. I spent some more time looking around and saw there was a config option in the configure.ac that checked for pthread support to enable the input thread. Since it now uses meson, I checked the meson options file and didn't see a single thing in there mentioning input thread.

Current Hypothesis: I think they forgot to transfer over the input thread enable bits when they converted over to Meson, causing the build to disable the input thread.

Honestly, I have little faith that my hypothesis is correct because it's kind of a stupid mistake, and there are mentions of input thread in other Meson build files, just not anything checking for support and explicitly enabling it. But it is the closest I have to an answer of why as of yet.

Thoughts?