BUG: Multiple Keyboards Lag

[Carlos Garnacho]

Hi,

On Mon, Oct 11, 2021 at 12:16 AM Ryan McClue <re.mcclue at protonmail.com> wrote:
>
> PROBLEM:
> I'm on a fresh install of Ubuntu 20.04 (xorg 1.20.11), with 2 connected keyboards (built-in and USB).
> When I hit keys on each keyboard simultaneously in a program like firefox, gnome-terminal etc. stalling/lag occurs.
> It only happens for keyboards it seems as moving an external mouse and trackpad together causes no issues.
>
> TO REPRODUCE:
> To investigate the problem I wrote a simple C file (see attached 'xorg-lag.c', compile with $(gcc xorg-lag.c -o xorg-lag))
> The program finds keyboard devices under /dev/input/event and uses epoll to poll them for input via the evdev interface.
>
> If I start entering keys on one keyboard and then switch to the other, the program stalls briefly.
> If I simultaneously enter keys on each keyboard the program stalls indefinitely until I stop entering keys.
> I have tested with different keyboards and experience the same result.
> If I switch to a virtual terminal and run I experience no lag.
> This makes me think it is a bug with xorg.

It sounds like you mean
https://gitlab.gnome.org/GNOME/mutter/-/issues/398 (although
https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/1858 has more
recent context). I don't think there's a single culprit here, and
they're likely just indirectly relevant in this mailing list.

Cheers,
  Carlos