I don't know what would cause a second or more of keyboard-specific delay.
Hmm.
I think the first step I'd try is running them in windowed mode with evtest
running in a terminal alongside your game, so that you can see both at once. That can display a list of all keyboard events as they come in. If evtest
is showing the events immediately as they come in, but Doom isn't responding quickly, then the kernel is reporting the events quickly, and it's Doom not processing them quickly. If evtest
is delaying display, then there has to be something at the hardware or kernel level that's problematic.
That won't alone solve your problem, but it'll help narrow down what the cause is.