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. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1800550 Title: Xorg freeze To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1800550/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs