Hello Lukas,
Firstly, could you provide output of the following command (requires mesa-demos): `glxinfo|grep Rendering`
$ glxinfo|grep -i rendering
I had an issue like this with KDE having huge lag problems. I checked htop and determined it was caused by applications dropping into uninterruptible sleep due to I/o wait. That in turn was caused by baloo file indexer running rampant in my huge music collection. Baloo is disabled, I already noticed the high CPU usage right after installing KDE. Furthermore, the issue appeared before installing KDE. Not sure if yours would be the same problem, but you could check htop and see if there applications that are lagging are in state D .. that would mean something is using the hard drive and they have to wait. Just ran htop to make sure, and no applications are in "D" state when something is lagging, only "R" and "S". I already checked before that the hard drive isn't the culprit (using iotop and dstat), as well as RAM (no more than 10% used). (My apologies for top posting, on mobile) No troubles, thanks for taking your time :) direct rendering: Yes
glxinfo furthermore says: Extended renderer info (GLX_MESA_query_renderer): Vendor: Intel Open Source Technology Center (0x8086) Device: Mesa DRI Intel(R) HD Graphics 520 (Skylake GT2) (0x1916) Version: 19.1.7 Accelerated: yes Video memory: 3072MB Unified memory: yes Preferred profile: core (0x1) Max core profile version: 4.5 Max compat profile version: 3.0 Max GLES1 profile version: 1.1 Max GLES[23] profile version: 3.2 So indeed the HD 520 seems to be doing all the work, with the NVIDIA Quadro idling around.