Can I switch graphics drivers without deinstalling?

[Mister Pi]

You have to change the blacklist place a hash mark before #nouveau and it will be loaded on next boot.
Then you'll have to add Nvidia to the blacklist (blacklist nvidia) and it will not load the next boot.

Yes, I know commenting out. But wasn't sure about how to specify the driver in the blacklist. I take from your post that "blacklist" doesn't require an exact string match, and "blacklist nvidia" will block any driver containing the substring "nvidia"?

[Mister Pi]

So your black list will look like this when using nouveau
#blacklist nouveau
blacklist nvidia

The blacklist file put there by NVIDIA reads:

blacklist nouveau
blacklist lbm-nouveau
alias nouveau off
alias lbm-nouveau off

So what is the lbm-* for? And should I add corresponding aliases for nvidia? Like

alias nvidia off
alias lbm-nvidia off

[Mister Pi]

Or perhaps a bash script to make the change.

I was thinking of having two files, and swapping one out, rather than fiddling with commenting out/in each time. The man page for modprobe.d says it looks at *.conf files. So if I change /etc/modprobe.d/foo.conf to /etc/modprobe.d/foo.nonconf will it be completely ignored?

[Mister Pi]

So after some searching, reading man pages, and trial-and-error, I did the following:

1. Moved the NVIDIA blacklist file /etc/modprobe.d/nvidia-graphics-drivers.conf (the one that blacklists the nouveau driver) to /etc/modprobe.d/nvidia-graphics-drivers.NOconf
2. Made a new file with the original name containing:

blacklist nvidia
options nvidia modeset=0

3. Did

sudo update-initramfs -u

4. Rebooted

I could tell something was different because in the Plasma startup screen, the little half circle that spins around while it's working would spin much faster with the Nvidia driver. Also, lsmod no longer listed any nvidia devices.

And glmark2 gave lower scores:

Intel graphics: 2180
NVIDIA GPU with nouveau: 2128
NVIDIA GPU with nvidia-390 driver: 4658

This is on a laptop with an Intel i7-8550U at 1.8GHz (but lscpu says it's
running at 2.5GHz) and a GeForce MX150 GPU.

The second number is lower than the first, but I'll call that noise.
I'm not sure whether this means the first test did not properly disable the GPU
or the Nouveau driver is not very good (at least for glmark2).

[kc1di]

The Nouveau driver is an open source driver that was basically reversed engineered and may not have all the functions that the Propriety Nvidia driver has. So I think your test is quite good.

At least that has been my experience with nvidia cards and drivers.

[GreyGeek]

https://unix.stackexchange.com/quest...-eth0-on-linux

[Mister Pi]

The Nouveau driver is an open source driver that was basically reversed engineered and may not have all the functions that the Propriety Nvidia driver has. So I think your test is quite good.

IDK... Seems like glmark2 is saying a GPU with Nouveau is no better (or marginally worse) than the builtin graphics. I would've expected the score to land somewhere between the other two. IOW, if I don't want to use the proprietary driver, I might as well not use the GPU at all! At least that's what glmark2 is telling me.

I don't object to using a proprietary driver per se... but it seems to be causing other problems on my system, as I say on another thread (https://www.kubuntuforums.net/showth...reen-is-broken). Seems like I'll have to switch back and forth according to whether or not I need the perf (I originally installed the NVIDIA driver to use CUDA).

[Mister Pi]

So after some searching, reading man pages, and trial-and-error, I did the following:

Unfortunately, that wasn't quite enough. When I got some audio pops on VLC, I discovered the systemd-udevd process was eating up 100% of the CPU (according to top, so that's one core), and another systemd-udevd process was taking up another 10%.

After some searching, I tried "udevadm monitor" and saw some error msgs about nvidia modeset, so I commented out the "options nvidia modeset=0" line in my blacklist file, reran "sudo update-initramfs -u" and rebooted. Now instead of one or two systemd-udevd processes eating up lots of CPU cycles, there were *25* of these, although each one only took up 1 or 2%. Also, /var/log/syslog was expanding at about 100 lines a second.

So I found that installing the Nvidia driver had added a file /lib/udev/rules.d/71-nvidia.rules, so I did

sudo touch /etc/udev/rules.d/71-nvidia.rules

which created a blank file which overrides the other rules file (according to the man page for udev). After rebooting, there is only one systemd-udevd process and it seems well-behaved.