Re: PROBLEM: Evdev epoll_wait Lag

["dmitry.torokhov@gmail.com" <dmitry.torokhov@gmail.com>]

Hi,

On Fri, Oct 08, 2021 at 11:29:51PM +0000, Ryan McClue wrote:
> Hi there,
> 
> PROBLEM:
> 
> I'm on a laptop, 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 'evdev-lag.c', compile with $(gcc evdev-lag.c -o evdev-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 do not observe stalls but did you mean to essentially busy-loop in
your program? epoll_wait with 0 timeout causes it return immediately,
you want to use -1 if you want to wait indefinitely or give it a real
timeout.

Thanks.

-- 
Dmitry