Hello,
I'm on Tumbleweed with Plasma 5.8.4 and I'm having some issues with KWin's compositing (GTX 1070 with 375.26).

1. I have to export __GL_YIELD=USLEEP to prevent tearing. Not a big thing, but it would be more convenient if it worked ootb.

2. KWin's vsync doesn't seem to be perfect. I sometimes notice repeated frames, e.g. in old games with vsync turned on or in Firefox (with its OpenGL rendering enabled) at http://www.vsynctester.com.
The mentioned applications work fine without any compositor and with their own vsync internally enabled, there is zero vsync stutter then.

3.) I can still confirm this old problem reported by someone else:
viewtopic.php?f=111&t=128058
Apart from that non-perfect vsync stutter mentioned in 2.) (which usually happens once every ~30 seconds or so), there is a lot of additional stutter with mpv. As soon as I turn off KWin compositing, any stutter is entirely gone (power profile is already set to maximum performance in driver).

I've already tried every possible tweak or configuration I could fine, without success (in compositor settings, mpv settings and Nvidia driver settings).

Well, I simply gave up on KWin compositing on Nvidia. I think it's just broken.
What works is Compton with xrender and vsync forced via driver (ForceFullCompositionPipeline).

I too would like to voice my concern with number 2.

Intel GPU on a haswell CPU for me. I have tried both the standard driver given by Kubuntu 17.04, AND Modesetting, both result in the same exact stuttering nonsense.. Your test outlines the problem that KDE seems to suffer with most for me. Unity, and Gnome do not have these issues.

I made a video detailing this issue. https://www.youtube.com/watch?v=iDG_yiqL5CQ

Moving the mouse seems to aggravated your number 2 issue.

This is on the stock Kubuntu 17.04 install, and even tried using modesetting, and all of the vsync options.

aufkrawall, I just fixed number 2 on my Intel GPU, however it may or may not work on your GTX 1070, as Nvidia seems to be backwards to this.

For me I created /etc/profile.d/kwin.sh

and then added just one line
export KWIN_TRIPLE_BUFFER=0

Rebooted, and that misaligned vsync is completely gone, no more stuttering.. Though from what I understand, Nvidia likes that number to be 1, not 0.. But worth a shot!

EDIT: Can confirm on my Radeon this also fixed any stuttering as well. So this appears that Kwin by default is triple buffering. This should be a no-no in my opinion. Not all drivers are set up for them by default. About the only real benefit for this seems to be JUST nvidia cards.

Hi,
I've just discovered your reply. Now I'm also with Radeon & amdgpu/mesa and I can confirm that your method really seems to do the trick!
I tested
-scrolling in Firefox
-video playback in mpv
-vsync in games
-moving windows
and everything seems to be absolutely smooth with TB=0.

Thanks a lot for your hint!

PS: I'm still the user "aufkrawall" in case my username is shown differently now, I had some hassles with the new forum auth.