Back in early 2015 I encountered an issue with NetworkManager: Even if you have ever only told it about your one single wireless network (or AP, access point) it insists on scanning the airwaves at regular intervals (about every two minutes) looking for a better connection. I thought that was dumb. This behaviour is known to the developer and is working-as-intended. There is no off-switch. I thought that was really, seriously dumb. I still do.
It was not an issue for me until I tried live streaming, specifically using Steam’s in-home streaming that allows you to play a game on a different computer to the one you’re sitting at and streaming the ‘playback’ to your current machine. Then NetworkManager cuts into the smooth streaming every two minutes, turning it into a screenshot slideshow instead for 3-5 seconds. If you’re playing a game that requires attention to not dying/crashing/clicking-the-wrong-button, this is a bad thing for a long time.
Now, my gaming desktop died shortly afterwards (note to self: Never buy another (cheap) Corsair PSU as long as you live) so it quickly became a non-issue. I recently got a new gaming computer, dual-booting Windows 10 and Ubuntu
16.04 17.04. Coupled with a new 802.11ac wireless network it seemed obvious to try to make in-home streaming work with the desktop-to-HTPC streaming, essentially making the HTPC a high-end Steam Link, rather than a low-end gaming computer in it’s own right. Running the streaming ‘server’ from Windows, everything works. Streaming from linux I was instantly reminded of the problems I had two years ago.
About half a year ago, commenter William Bernting kindly added some information to my original post suggesting how to make NetworkManager stop the scanning routine. I hope it works for whoever finds this information and I should probably have tested his solution before forging ahead with my own, more radical one. However, I have no patience with NetworkManager anymore, I do only connect to one network and I had the impetus last night so here is what works for me: Rip out NetworkManager, replace with systemd-networkd.