pi400kb uses 100% CPU on one core

[Hermann-SW]

Could be fixed by adding an usleep() in main processing loop: https://github.com/Gadgetoid/pi400kb/blob/feature/toggle-hook/pi400.c#L202-L248

[Gadgetoid]

WHOOPS! Yeah. That's a bit silly of me.

[Hermann-SW]

I added "usleep(100)" at end of main loop, resulted in 16.5% CPU. Replaced with "usleep(1000)", resulting in <4% CPU on one core. Finally used 10000, sleeping for 1/100th second should be OK for keyboard and mouse, resulting in <1% CPU utilization.

Just verified that it is OK by running cpuburn-a53 on same Pi400 and still getting fast keyboard as well as mouse reaction.

Could be enhanced by doing usleep() in a loop only if neither key nor mouse events happened in that loop.

pi@raspberrypi400:~/pi400kb/build $ top -b | grep pi400kb$
32191 root      20   0    2040    404    344 S   0.0   0.0   0:00.12 pi400kb
32191 root      20   0    2040    404    344 S   0.3   0.0   0:00.13 pi400kb
32191 root      20   0    2040    404    344 S   0.7   0.0   0:00.15 pi400kb
32191 root      20   0    2040    404    344 S   0.0   0.0   0:00.15 pi400kb
32191 root      20   0    2040    404    344 S   0.7   0.0   0:00.17 pi400kb
32191 root      20   0    2040    404    344 S   0.3   0.0   0:00.18 pi400kb
32191 root      20   0    2040    404    344 S   0.3   0.0   0:00.19 pi400kb
^C
pi@raspberrypi400:~/pi400kb/build $ 

[gpetersson]

I would recommend using poll or epoll (or even select) instead of a usleep since it is designed exactly to solve this problem... it will wait (efficiently) until there is activity on any of the file descriptors you are watching.

[Gadgetoid]

@gpetersson agreed- forgot about those! This grew from a very rough gist prototype into a more mature project quite suddenly 🤣

[normen]

I made a PR that uses poll(), if only for testing. Seems to work fine for me, basically 0% CPU load.