dmesg | grep bbswitch
[ 3031.384683] bbswitch: version 0.8
[ 3031.384689] bbswitch: Found integrated VGA device 0000:00:02.0: \_SB_.PCI0.GFX0
[ 3031.384694] bbswitch: Found discrete VGA device 0000:01:00.0: \_SB_.PCI0.PEG0.PEGP
[ 3031.384782] bbswitch: detected an Optimus _DSM function
[ 3031.384816] bbswitch: device 0000:01:00.0 is in use by driver 'nvidia', refusing OFF
[ 3031.384817] bbswitch: Succesfully loaded. Discrete card 0000:01:00.0 is on