[Bug 99634] keypress is delayed to keyrelease on rotated screen in xorg 1.19

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99634

--- Comment #8 from Frederick Eaton <frederik-freedesktop at ofb.net> ---
Thank you Sven for being the first reproducer, and also for observing the
stalled blinking cursor, which perhaps elucidates why the bug is connected to
the graphics driver. (I try to avoid blinking things)

I re-confirmed that I only experience the bug with a rotated screen, but I
experimented a bit to try to understand the connection to graphics updates. If
I open a window and run

    while true; do perl -le 'print rand()'; sleep 0.01; done

then when I try to type in another window, the keypresses are *not* delayed.
This random-number loop also eliminates the delay I saw in the 'xev' output. I
don't understand why this should be. If the graphics updates are being delayed
until an event occurs or 200ms elapses, then the output of the random number
loop should be jerky - but it is not. If the graphics updates are triggered by
a new line appearing in the terminal, but not by a single character or a
blinking cursor, then 'xev' should not have shown a delay, as it outputs
several lines per keypress.

Another thing I don't understand is why this appeared in xorg-server 1.19.1. I
think 1.19 made some kind of change to use 'libinput' as the default, at least
in Arch - certainly when I downgraded I had to install a package called
"xf86-input-evdev" to fix up the dependencies, which is an alternative to
"xf86-input-libinput". The 1.19.1-1 package depends on "xf86-input-libinput",
while the 1.18.4-1 package only dependen on the 'virtual package'
"xf86-input-driver". Does this bug have a connection to libinput, or is that
just a coincidence?

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