I want the epoll_wait to return immediately if no data, so I believe the timeout of 0 is correct. I'm using an adapted version of this loop for a hobby program. However, every time I open it up in a debugger (or just normally) htop shows CPU usage for the process is ~97% and the CPU fan becomes very loud. Like I said, I'm experiencing stalls from a fresh install of Ubuntu in all native applications like gnome-terminal, firefox, gedit, vi etc. I don't understand what is going on or how to go about debugging it. -- Ryan McClue, Sydney ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Saturday, October 9th, 2021 at 2:19 PM, dmitry.torokhov@xxxxxxxxx <dmitry.torokhov@xxxxxxxxx> wrote: > 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
