I'm Jason Firth.
Sometimes it's a real struggle going through and trying to find out how to do something, and when you find a simple answer you just wish someone else had written it down.
I have a Dell Latitude E5440 I got off of eBay. Great little machine. It has a decent screen for the era, 8GB of DDR3 memory, I put a 512GB SATA SSD into it, I really like this little thing! I initially installed Windows 10 on it, but I wasn't happy with how it ran. It just didn't quite seem like the machine it was, so I kept moving.
I eventually decided to put Ubuntu Linux 21.04 onto it, since that more or less met my use case.
The problem I had is that the Geforce GT 720M is a really strange model. Even trying to get drivers for Windows 10 was challenging, and that's rarely a problem!
Normally in Ubuntu, you'll just go to the driver manager, and then go to "additional drivers", and any proprietary devices will be shown. Unfortunately, the Geforce GT 720M was not shown on this window.
I tried a few different things, including the bumblebee optimus program, but I didn't want to run certain programs using the Geforce, I wanted to run all my programs including compositing using the Geforce.
Finally, I found the solution!
First, I had to get rid of the nouveau open source video driver
sudo apt-get purge xserver-xorg-video-nouveau
Second, I ran an autoremove just to clean things up.
Finally, I had to install the 390 series driver. This particular version is important because the 720M is actually a 600 series card.
After a quick reboot, I didn't immediately see a difference, but there was now an nvidia X Server settings item in my menu. Going into it, I was able to select "performance mode (nvidia)" which ensures the discrete GPU is always doing the heavy lifting when displaying graphics.
I don't think a lot of people have Dell Latitude E5440s running a Geforce GT 720M discrete graphics chip, so there weren't a lot of clues about where to start. Hopefully from now on people searching for the solution to this problem can find the solution in this post.
Thanks for reading!