CPU usage is too high when clone device by v4l2loopback

[trungthanhnguyen0502]

I use v4l2loopback + Gstreamer to clone device. Sometimes Using this plugin results in very high CPU usage.

Step 2: Environment

• v4l2loopback version: v0.12.7 and main (9ba7e29)
• kernel version: 5.10.104-tegra
• Distribution (+version): Ubuntu 20.04.5 LTS
• Jetson xavier nx: JetPack 5.0.2.
• Deepstream and Gstreamer version are 6.1.1 and 1.16.3.

Step 3: Describe the problem:

Steps to reproduce:

1. Create virtual devices:
   sudo modprove v4l2loopback devices=3

2. Clone the data stream from the original device to virtual devices.

gst-launch-1.0 v4l2src device=/dev/video0 ! videorate drop-only=true ! "video/x-raw,framerate=(fraction)30/1" !
tee name=t ! queue ! v4l2sink device=/dev/video1 sync=false async=true
t. ! queue ! v4l2sink device=/dev/video2 sync=false async=true
t. ! queue ! v4l2sink device=/dev/video3 sync=false async=true

Observed Results:

• In good case, CPU usage like that:

• but most of the cases i run this gst-launch command, CPU usage is too high. like that:

Or worst case like that:

I've checked and not see any strange programs that can cause this problem. I see that someone else had the same problem, Nvidia supporter said "For CPU usage, it is probably v4l2loopback as well causing high CPU load. high-cpu-usage-for-video-capturing

Expected Results:

I want to know why CPU usage is too high and how to fix it. Because this problem affects my system a lot.

[umlaeute]

hmm, well.
the high CPU load you see is obviously in user-space (the green bar), which is GStreamer.
the load in kernel-space (the red bar), which is where you would see anything done by v4l2loopback, seems to be pretty constant.

so i conclude that the v4l2loopback is not doing any excessive work, but instead GStreamer is.
(it could still be a problem with v4l2loopback that makes GStreamer burn your CPU cycles).

so, if I were you, i would do some analysis where GStreamer is spending its time (and see whether something can be done on the v4l2loopback side of things)

[trungthanhnguyen0502]

I tried some analysis with simple gstreamer command. When I run
gst-launch-1.0 v4l2src device=/dev/video0 ! videoconvert ! appsink
CPU usage is 17%.

But when I replace appsink with v4l2sink (to a virtual device created by v4l2loopback). CPU usage is 60%.

[chrisiberg]

I think your problem hast to do with missing DMA support, or am I wrong? @umlaeute
#501

[sanbrother]

I think your problem hast to do with missing DMA support, or am I wrong? @umlaeute #501

Will copy without DMA consume a lot of CPU? mmap still costs high CPU usage?

[angeelalg]

• kernel version: 5.10.104-tegra
• Distribution (+version): Ubuntu 20.04.5 LTS
• Jetson xavier nx: JetPack 5.0.2.
• Deepstream and Gstreamer version are 6.1.1 and 1.16.3.

Hello @trungthanhnguyen0502 , good morning.

How did you get v4l2loopback working for you? I'm trying to get my Jetson NX to work, with the same kernel version and it's impossible. I keep getting this error when running modprobe v4l2loopback:
modprobe: ERROR: could not insert 'v4l2loopback': Operation not permitted