which process is using nvidia module?

Question

I've got bumblebee 3.0 installed, I started chromium-browser with optirun and although I have closed chromium off, the card is still on. How can I know which process is using nvidia module that prevents the card from switching off?

root@magneto:/# cat /proc/acpi/bbswitch 
0000:01:00.0 ON
root@magneto:/# 
root@magneto:/# tee /proc/acpi/bbswitch <<<OFF
OFF
root@magneto:/# cat /proc/acpi/bbswitch 
0000:01:00.0 ON
root@magneto:/# dmesg |tail -1
[92040.608982] bbswitch: device 0000:01:00.0 is in use by driver 'nvidia', refusing OFF
root@magneto:/# 

Answer 1

I've noticed that Flash sometimes turns the card automatically on and then loads the driver. If the module is not used you can safely unload it after which you manually disable the card:

sudo rmmod nvidia
sudo tee /proc/acpi/bbswitch <<<OFF

If the driver cannot be unloaded, it will display:

ERROR: Module nvidia is in use

There is not much that you can do about that. A CUDA application of Xorg server is possible using it. You can check it with:

lsof -n -w -t /dev/nvidia*

It'll return a PID list unless you remove -t.