I ran perf during the bug to see if I could find out where the high CPU usage is coming from since it isn't leaving a .crash file. I sampled for 10 seconds starting immediately after plugging in the 4k monitor.
By PID the report looks like:
Samples: 47K of event 'cycles:ppp', Event count (approx.): 43897790507
Children Self Pid:Command
+ 34.78% 34.78% 1763:Xorg
+ 30.11% 30.11% 0:swapper
+ 12.03% 12.03% 139:kworker/u8:2-ev
+ 11.98% 11.98% 202:kworker/u8:4-fl
+ 4.91% 4.91% 415:kworker/1:2-eve
2.51% 2.51% 1943:gnome-shell
1.16% 1.16% 2183:nautilus-deskto
0.73% 0.73% 2659:Web Content
So xorg and kernel calls are making up 63.7% with just 4.4% as noise and
30.11% idle.
Sorting by symbol:
Samples: 47K of event 'cycles:ppp', Event count (approx.): 43897790507
Children Self Symbol
- 47.40% 47.35% [k] ioread32
- 23.83% ret_from_fork
kthread
worker_thread
- process_one_work
+ 20.26% nv50_disp_atomic_commit_work
+ 3.55% nvif_notify_work
+ 9.32% 0x5593da5de690
+ 7.36% 0
+ 6.72% 0x5593da5dd3b0
It looks like ioread32 is getting called a lot by nouveau.
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https://bugs.launchpad.net/bugs/1800550
Title:
Xorg freeze
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