Edit: see here for the MathieuGras-TimRichardson solution:
I have two Optimus laptops, a Thinkpad P50 and a W520. I have just spent two hours testing 18.04 and it was a shocking experience.
prime sync is broken on both, despite a released fix.
EDIT: it works, but configuration is different, see below
But that’s nothing compared to the problems with prime-select.
This command line tool turns off or on the nvidia card.
On 17.10 and as far back as 16.04, it moves some libraries around, executes quickly and it works. You never ever end up with an unbootable machine. This is interesting to note, because not a single one of those things is true at the moment.
to change between intel-only and hybrid mode, it seems to install and uninstall packages, and it rebuilds the initramfs. This is very slow. But worse, if I leave it in intel mode and go to discrete graphics in the bios, the greeter doesn’t start, it just loops flashing the screen black and colorful very fast.
I have reported a new bug and suggested that the prime sync bug is not fixed. I have other strange situations: once I booted into discrete graphics, had my external monitors working, but had tearing on the laptop panel and nvidia settings said the nvidia driver was not loaded. How that is possible I have no idea. The tearing indicates that prime output is happening, but you’d think with discrete mode set in bios the intel card should be invisible, so I always thought. This is so weird I didn’t report a bug. Although perhaps that was just nouveau.
In 17.10 I permanently set prime-select intel and turn on discrete when back at my desk, which starts the machine in full nvidia mode (I don’t use hybrid graphics in nvidia mode because audio to my display port monitor doesn’t work).
That sure doesn’t work anymore. I thought I’d see if I can get to intel-only mode by blacklisting nvidia but that didn’t work: I have no external monitors, but judging by power consumption, the nvidia card was not turned off.
I think the cause of these problems is the multi-dispatch libglvnd innovation which sounded like it was going to make life better, allowing other distributions to reach the nice experience of Ubuntu. Sad to see that for Ubuntu, it is a disaster. I wonder why the 17.10 method was abandoned.
Is it time to look elsewhere? Bumblebee sounds wrong for me, since I want a Ubuntu 17.10-style multi-monitor experience where three monitors work as one desktop.