Occasional black screen flashing for approx 1/4 second

Occasionally (several times a day now, it seems to have gotten worse within the last few weeks) my left monitor goes completely black for about 1/4 - 1/2 second and the returns to normal. Whenever it happens, I have something like this in Xorg.0.log:

[ 54945.022] (EE) client bug: timer event0 debounce: scheduled expiry is in the past (-0ms), your system is too slow
[ 54945.022] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-13ms), your system is too slow

But note that I have more messages like that than screen flashes. In other words, as far as I’ve noticed, every time the screen flashes a corresponding message appears in the log. But, every time such an error is logged the screen does not necessarily flash.

Also, sometimes, but not every time (I think), I get this in the log when the screen flashes:

[ 55307.471] (--) NVIDIA(GPU-0): DFP-0: disconnected
[ 55307.471] (--) NVIDIA(GPU-0): DFP-0: Internal TMDS
[ 55307.471] (--) NVIDIA(GPU-0): DFP-0: 330.0 MHz maximum pixel clock
[ 55307.471] (--) NVIDIA(GPU-0): 
[ 55307.471] (--) NVIDIA(GPU-0): DFP-1: disconnected
[ 55307.471] (--) NVIDIA(GPU-0): DFP-1: Internal TMDS
[ 55307.471] (--) NVIDIA(GPU-0): DFP-1: 165.0 MHz maximum pixel clock
[ 55307.471] (--) NVIDIA(GPU-0): 
[ 55307.472] (--) NVIDIA(GPU-0): DELL S3221QS (DFP-2): connected
[ 55307.472] (--) NVIDIA(GPU-0): DELL S3221QS (DFP-2): Internal DisplayPort
[ 55307.472] (--) NVIDIA(GPU-0): DELL S3221QS (DFP-2): 2660.0 MHz maximum pixel clock
[ 55307.472] (--) NVIDIA(GPU-0): 
[ 55307.474] (--) NVIDIA(GPU-0): DFP-3: disconnected
[ 55307.474] (--) NVIDIA(GPU-0): DFP-3: Internal TMDS
[ 55307.474] (--) NVIDIA(GPU-0): DFP-3: 165.0 MHz maximum pixel clock
[ 55307.474] (--) NVIDIA(GPU-0): 
[ 55307.474] (--) NVIDIA(GPU-0): DELL S3221QS (DFP-4): connected
[ 55307.474] (--) NVIDIA(GPU-0): DELL S3221QS (DFP-4): Internal DisplayPort
[ 55307.474] (--) NVIDIA(GPU-0): DELL S3221QS (DFP-4): 2660.0 MHz maximum pixel clock
[ 55307.474] (--) NVIDIA(GPU-0): 
[ 55307.476] (--) NVIDIA(GPU-0): DFP-5: disconnected
[ 55307.476] (--) NVIDIA(GPU-0): DFP-5: Internal TMDS
[ 55307.476] (--) NVIDIA(GPU-0): DFP-5: 165.0 MHz maximum pixel clock
[ 55307.476] (--) NVIDIA(GPU-0):

I have a GeForce RTX 2060 SUPER with 2 monitors attached via DisplayPort (the graphics card has 2 ports so I have each monitor plugged into 1 port). Both monitors are 3840x2160. I’ve only observed the left (main) monitor flashing, never the right monitor.

I tried uploading nvidia-bug-report.log.gz but the website is giving an error. I’ll try uploading again after I post.

Email sent to linux-bugs@nvidia.com as I was unable to attach nvidia-bug-report.log.gz to this thread (the file is only 310KB).

Dis you already try swapping cables?

Hm, no that sounds obvious now that you say it. I’ll try that and see if the flashing follows the cable or remains on the left monitor.

I switched the cables only on the monitor ports, and to my surprise the left monitor remained as the left monitor and the right monitor remained the right monitor. I thought I would have to switch both the monitor ends and the card ends.

Anyway, the flashing is now on the right monitor. So either that cable is bad or that port on the video card. Next I’ll switch the cables at the video card side and see if the flashing remains on the right monitor (which would mean the cable is bad).

Ok weird… I haven’t messed with the cables yet (I was going to switch ports on the video card, but haven’t done it yet), but now the black screen flashing is back to the left monitor again.

I just ordered 2 new DisplayPort cables to test - should arrive tomorrow.

I tried the 2 new cables and still get the screen flashing. I already replied to nvidia support with the new nvidia-bug-report.log.gz. Right now the flashing is rare enough that’s it’s annoying, but not debilitating.

Thinking it might be KDE, I tried disabling the compositor in KDE, but that didn’t help.

Please check if disabling KDE’s kscreen2 service for testing prevents the flashing.

Ok, I just disabled KScreen 2 in KDE’s System Settings and will wait and see today if I get any flashing and/or “client bug” messages in /var/log/Xorg.0.log.

Soon after disabling KScreen 2 I had another screen flash. I logged out and logged back in and yesterday didn’t have any screen flashes. However, today I’m starting to have them again. I’ll note I am compiling some stuff in the background, so the system is under a decent load right now. Actually right now the flashing is really bad - 1 flash every 10 seconds or so.

But, throughout yesterday and today the “client bug” messages in /var/log/Xorg.0.log have persisted:

[ 95727.120] (EE) client bug: timer event0 debounce: scheduled expiry is in the past (-7ms), your system is too slow
[ 95727.120] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-20ms), your system is too slow
[ 96028.527] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-2ms), your system is too slow
[ 96253.230] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-9ms), your system is too slow
[ 96683.760] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-6ms), your system is too slow
[ 96840.673] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-7ms), your system is too slow
[ 96949.141] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-3ms), your system is too slow
[ 96983.335] (EE) client bug: timer event0 debounce: scheduled expiry is in the past (-0ms), your system is too slow
[ 96983.335] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-13ms), your system is too slow

Based on a hint from here: Display hangs routinely when using Browsers/Steam/Discord/VLC/etc / Newbie Corner / Arch Linux Forums

I bought an “Ultra High Speed HDMI” cable to plug my main monitor into my graphics card, to use instead of DisplayPort. I was unaware until last week that some versions of HDMI supported 4K. Anyway, the cable works and I get my full resolution. We’ll see if it also solves the black flashing problem. (The HDMI cables that came with my 4K monitors do not support 4K /rantoff.)

I have 2 monitors, but only 1 HDMI port. But, I’ve mainly only been experiencing the black flashing with my main monitor (not the secondary monitor), so hopefully this will work…

So far (about 1 1/2 working days) I haven’t had any screen flashing - it appears switching to the HDMI cable worked. I would rather just use 2 DisplayPort cables, rather than 1 HDMI cable and 1 DisplayPort cable, but it’s not worth further troubleshooting at this point.

I still get the following messages in /var/log/Xorg.0.log:

[107431.874] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-9ms), your system is too slow
[107437.136] (EE) client bug: timer event0 debounce: scheduled expiry is in the past (-1ms), your system is too slow
[107437.136] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-14ms), your system is too slow
[107458.405] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-12ms), your system is too slow
[108100.674] (EE) client bug: timer event0 debounce short: scheduled expiry is in the past (-9ms), your system is too slow

But I’m pretty sure that’s an unrelated issue. Originally I thought the 2 issues were connected, but now I’m pretty sure they’re different.

Ok, it’s now been a full week with no monitor flashing. My main monitor uses the HDMI cable and my secondary monitory uses a DisplayPort cable. One annoyance is that the DisplayPort monitor is used for bootup and console - they only switch to my preferred configuration after X starts. But that’s fairly minor.

I may occasionally try going back to 2 DisplayPort cables when upgrading the nvidia driver and will report if the issue ever resolves itself.

But for now, I will continue to use the HDMI cable workaround.