High CPU usage after capture on RPi Zero running showmewebcam

[okawo80085]

Problem Description:
The /opt/uvc-webcam/uvc-gadget -l -p 21 -b process keeps running and using more then 20% CPU after the host system finished capturing from the v4l2 device. CPU usage from top when connecting to the debug shell on the RPi Zero:

Before host started capture (idle):

Mem: 33600K used, 375412K free, 1516K shrd, 1108K buff, 16028K cached
CPU:   0% usr   2% sys   0% nic  97% idle   0% io   0% irq   0% sirq
Load average: 0.07 0.04 0.00 2/43 334
  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
  326   278 root     R     1880   0%   3% /opt/uvc-webcam/uvc-gadget -l -p 21 -b
  334   274 root     R     2756   1%   0% top
    1     0 root     S     7564   2%   0% {systemd} /sbin/init
   64     1 root     S     7520   2%   0% /usr/lib/systemd/systemd-udevd
   60     1 root     S     7104   2%   0% /usr/lib/systemd/systemd-journald
   93     1 dbus     S     5008   1%   0% /usr/bin/dbus-daemon --system --addres
   94     1 root     S     2756   1%   0% -sh
  274     1 root     S     2756   1%   0% -sh
  278     1 root     S     2628   1%   0% {start-webcam.sh} /bin/sh /opt/uvc-web
    8     2 root     SW       0   0%   0% [ksoftirqd/0]
   14     2 root     SW       0   0%   0% [kcompactd0]
   44     2 root     IW<      0   0%   0% [kworker/0:1H-kb]
  332     2 root     IW       0   0%   0% [kworker/0:0-eve]
  333     2 root     IW       0   0%   0% [kworker/0:1-eve]
    2     0 root     SW       0   0%   0% [kthreadd]
    5     2 root     IW       0   0%   0% [kworker/u2:0-ev]
    6     2 root     IW<      0   0%   0% [mm_percpu_wq]
    7     2 root     SW       0   0%   0% [rcu_tasks_trace]
    9     2 root     SW       0   0%   0% [kdevtmpfs]
   10     2 root     IW<      0   0%   0% [netns]

When host is capturing stream (streaming):

Mem: 34476K used, 374536K free, 1516K shrd, 1108K buff, 16028K cached
CPU:   5% usr  67% sys   0% nic  26% idle   0% io   0% irq   0% sirq
Load average: 0.70 0.28 0.10 2/43 335
  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
  335     2 root     RW       0   0%  35% [kworker/0:0-eve]
  326   278 root     S     2832   1%  29% /opt/uvc-webcam/uvc-gadget -l -p 21 -b
   39     2 root     SW<      0   0%   4% [vchiq-slot/0]
  277     2 root     IW       0   0%   3% [kworker/u2:2-mm]
  334   274 root     R     2756   1%   2% top
    8     2 root     SW       0   0%   0% [ksoftirqd/0]
    1     0 root     S     7564   2%   0% {systemd} /sbin/init
   64     1 root     S     7520   2%   0% /usr/lib/systemd/systemd-udevd
   60     1 root     S     7104   2%   0% /usr/lib/systemd/systemd-journald
   93     1 dbus     S     5008   1%   0% /usr/bin/dbus-daemon --system --addres
   94     1 root     S     2756   1%   0% -sh
  274     1 root     S     2756   1%   0% -sh
  278     1 root     S     2628   1%   0% {start-webcam.sh} /bin/sh /opt/uvc-web
   14     2 root     SW       0   0%   0% [kcompactd0]
   44     2 root     IW<      0   0%   0% [kworker/0:1H-kb]
  333     2 root     IW       0   0%   0% [kworker/0:1-eve]
   40     2 root     SW<      0   0%   0% [vchiq-recy/0]
   42     2 root     IW       0   0%   0% [kworker/0:2-eve]
    2     0 root     SW       0   0%   0% [kthreadd]
    5     2 root     IW       0   0%   0% [kworker/u2:0-ev]

When host finished capturing (should be idle again):

Mem: 33756K used, 375256K free, 1516K shrd, 1108K buff, 16028K cached
CPU:   9% usr  21% sys   0% nic  68% idle   0% io   0% irq   0% sirq
Load average: 0.55 0.31 0.12 1/43 335
  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
  326   278 root     S     1880   0%  26% /opt/uvc-webcam/uvc-gadget -l -p 21 -b
  334   274 root     R     2756   1%   3% top
    8     2 root     SW       0   0%   0% [ksoftirqd/0]
    1     0 root     S     7564   2%   0% {systemd} /sbin/init
   64     1 root     S     7520   2%   0% /usr/lib/systemd/systemd-udevd
   60     1 root     S     7104   2%   0% /usr/lib/systemd/systemd-journald
   93     1 dbus     S     5008   1%   0% /usr/bin/dbus-daemon --system --addres
   94     1 root     S     2756   1%   0% -sh
  274     1 root     S     2756   1%   0% -sh
  278     1 root     S     2628   1%   0% {start-webcam.sh} /bin/sh /opt/uvc-web
  335     2 root     IW       0   0%   0% [kworker/0:0-eve]
   39     2 root     SW<      0   0%   0% [vchiq-slot/0]
  277     2 root     IW       0   0%   0% [kworker/u2:2-mm]
   42     2 root     IW       0   0%   0% [kworker/0:2-eve]
   14     2 root     SW       0   0%   0% [kcompactd0]
   44     2 root     IW<      0   0%   0% [kworker/0:1H-kb]
  333     2 root     IW       0   0%   0% [kworker/0:1-eve]
   40     2 root     SW<      0   0%   0% [vchiq-recy/0]
    2     0 root     SW       0   0%   0% [kthreadd]
    5     2 root     IW       0   0%   0% [kworker/u2:0-ev]

Expected behavior:
1-5% CPU usage by /opt/uvc-webcam/uvc-gadget -l -p 21 -b on idle after the host system finishes capturing from the v4l2 device.

Additional Notes:
The issue goes away if i restart the RPi, however that is not fitting my use case. In my use case the RPi is plugged in indefinitely into a VR system, wasting more power on idle is the last thing i want.

Host OS: Ubuntu 20.04.3 LTS
Board Running showmewebcam : Raspberry Pi Zero

uname -a from the board: Linux piwebcam 5.10.11 #1 Mon Nov 8 06:25:02 UTC 2021 armv6l GNU/Linux

Would be nice to see some sort of work around/solution to this! If its possible to enforce that state via shell commands that works for me too!

[okawo80085]

Originally reported on showmewebcam issue tracker in issue#178