Once upon a time XFree86 and Xorg updated the pointer directly in a SIGIO handler. But that's ancient history at this point, and nowadays I wouldn't expect Way

Once upon a time XFree86 and Xorg updated the pointer directly in a SIGIO handler. But that's ancient history at this point, and nowadays I wouldn't expect Wayland and Xorg to have a hugely different situation in this area. IIRC it all started going downhill in Xorg when glamour appeared. After the cursor rendering path wasn't async-safe for execution from the signal handler (which something opengl-backed certainly wouldn't be), the latency was worse. I remember when even if your Linux box was thrashing your mouse pointer would stay responsive, and that was a reliable indicator of if the kernel was hung or not. If the pointer prematurely became unresponsive, it was because you were on an IDE/PATA host and needed to enable unmask irq w/hdparm. An unresponsive pointer in XFree86 was that useful of a signal that something was wrong or misconfigured... ah, the good old days.