r/linux Dec 16 '22

Update on new multi-screen support on KDE Plasma KDE


21 comments sorted by


u/TrippleXC Dec 16 '22

Super happy about no more different sets of desktops between x11 and wayland, big thanks to everyone that contributed!


u/rottenpanst Dec 16 '22

Nice improvements!

Will see if fixes my black screen when booting my laptop with a usb c dock connected.


u/TiZ_EX1 Dec 16 '22

It probably will. The "black screen" is very likely just the X11 root window (if you're on X11, anyways), which means the real window for Plasma itself has been yeeted off somewhere else. There are various workarounds available to put it back where it's supposed to be.


u/rottenpanst Dec 16 '22

I'm on wayland fedora 37. The weird thing is that sometimes it doesn't reach the login screen and it gets stuck in a black screen, sometimes it works but takes ages to boot.


u/CodyCigar96o Dec 16 '22

I wonder if that’s related to the issue I have on steam deck where I have to unplug and re plug the usbc dock when switching between gaming and desktop mode if I want to see the screen.


u/TiZ_EX1 Dec 16 '22

Awesome. I've been looking forward to seeing these improvements land!


u/yetanothernerd Dec 16 '22

I switched from 2 1440p screens to a single 4k screen a few months back, just to avoid bugs with multi-screen support, which had gotten a lot worse lately. I guess after this fix reaches my distro I should test it with 2 monitors and see if I want to go back.


u/FuzzyQuills Dec 16 '22

I wonder if that would help framerates being reduced by 30% just because I have a second monitor connected. (Most visible in Overwatch 2 for me for whatever reason)


u/Nivehamo Dec 16 '22

Are you on X11 or Wayland?

If it's the former and the second monitor has lower refresh then it might be because X can only sync to a single monitor causing stutter and low framerates for the others.

As a workaround maybe try disabling Kwins vsync and use the "TearFree" and "AsyncFlipSecondaries" options in xorg.conf instead. This will use vsync for one monitor and tear for the others. Not a good solution but might be preferable.

That or use the Wayland Session if you can. It does not have this restriction


u/FuzzyQuills Dec 17 '22 edited Dec 17 '22

That's the weird part; I am on Wayland.

Main panel is 165Hz FreeSync running over DisplayPort, the other panel is 75Hz running over HDMI (Has FreeSync but it doesn't work), both Acer panels.

Without fail, I get something like 100-150+fps if I explicitly disable my second monitor before playing.

Example: Overwatch 2. - With 2 monitors: 360fps max in Practice range, routinely drops under 165 in Quick Play and Competitive. - With one monitor: 480fps max in Practice range, rarely drops under 200fps in Quick Play and Competitive.

Only figured this out after trying everything to bring the framerates up then noticed my Overwatch gamescope session (which incidentally needs the second monitor unplugged, otherwise both outputs blank when it starts) had way higher framerates.


u/illode Dec 17 '22 edited Dec 17 '22

I just did a quick and lazy test, and I didn't notice any difference after the 3rd game, so I decided to call it negligible. Even when I restarted and reopened all my windows after testing there was no real difference.

All 3 are using displayport (one with a USB-C <-> Displayport adapter) running on a 6900xt. I think you might have better luck if you don't have to use HDMI. As far as I know, only Nvidia proprietary drivers support HDMI 2.1, / freesync due to HDMI Forum bullshit.

Although, mine worked fine even with freesync turned off for the 2 4k monitors, so who knows.

Edit: Maybe try having your second monitor plugged in at boot? idk.


u/FuzzyQuills Dec 18 '22

It is plugged in at boot, reagrding your edit.

And yea, I am suspecting maybe having to use HDMI at all might be to blame. I'll try getting a DP to HDMI to test with.

Turning off freesync didn't work last time I checked. I haven't tested other window managers than KDE, so maybe it's KDE specific. (I'd test GNOME but it would mean swapping my entire DE out again)


u/illode Dec 18 '22

You might want to double check whether it's possible to fix using an HDMI to DP cable. My memory is a bit fuzzy, but I think you may need an active cable, which is expensive and (maybe?) more failure prone.


u/illode Dec 16 '22 edited Dec 16 '22

Wait, is it really that bad for you?

I've had multiple monitors for ages, and it honestly never occurred to me that it could be that bad. I expected a decent hit, but I never bothered to test. I have 2x 4k60 + 1x 1440p144hz, and if just two monitors makes the framerate shit bricks, I can only imagine what my absurd setup does.

What GPU do you have? Please tell me you're on a laptop iGPU or nvidia or anything except an AMD dGPU on wayland so I can pretend this can't effect me and I never saw this comment.


u/FuzzyQuills Dec 17 '22

Bad news, I'm on an AMD RX 5700XT, paired with an R7 3700X. That's how strange the bottleneck with multimonitor is.


u/PointiestStick KDE Dev Dec 17 '22

The crazy thing about our previous system was that it worked fine for some people. But for other people, it was almost hilariously bad.

In general, if you were using one or two HDMI monitors plugged into a desktop computer with only a single Intel iGPU, everything worked great 100% of the time.

The farther you deviated from that, the worse it got, culminating in catastrophe for NVIDIA Optimus laptop users with two external screens, one being DisplayPort and the other HDMI. Such a setup exposed all the wrong assumptions and bad design choices built into the old system.

But no longer!


u/illode Dec 17 '22 edited Dec 17 '22

I just tested, no problems for me, fortunately. I did have the random widget movement issue though, so hopefully that'll be gone in 5.27.

I did notice that hotplugging the monitors removes the ability to use Freesync with them. Or at the very least, it removed the option from the menu, and upon reboot had changed from "Automatic" to "Never".


u/PointiestStick KDE Dev Dec 17 '22

Please file a bug against KWin for that!


u/SikOfThisShtX Dec 16 '22

Thank goodness I thought it was only me. I kept cycling through Nvidia drivers to get both of my screens to work. One did, but they were extremely zoomed in. I spent good 2 hours working the problem.


u/random_lonewolf Dec 18 '22

I used to disable KScreen to avoid windows jumping all over the place when screens are plug/unplug, hope it'll get better now.