Update and request from upstream: "I have looked at the dump and there is something very odd for system.slice task group where the display manager is running. system.slice->tg_load_avg is around 381697 but tg_load_avg is normally equal to Sum of system.slice[cpu]->tg_load_avg_contrib whereas Sum of system.slice[cpu]->tg_load_avg_contrib = 1013 in our case. We can have some differences because the dump of /proc/shed_debug is not atomic and some changes can happen but nothing like this difference.
The main effect of this quite high value is that the weight/prio of the sched_entity that represents system.slice in root cfs_rq is very low (lower than task with the smallest nice prio) so the system.slice task group will not get the CPU quite often compared to the user.slice task group: less than 1% for the system.slice where lightDM and xorg are running compared 99% for the user.slice where the stress tasks are running. This is confirmed by the se->avg.util_avg value of the task groups which reflect how much time each task group is effectively running on a CPU: system.slice[CPU3].se->avg.util_avg = 8 whereas user.slice[CPU3].se->avg.util_avg = 991 This difference of weight/priority explains why the system becomes unresponsive. For now, I can't explain is why system.slice->tg_load_avg = 381697 whereas is should be around 1013 and how the patch can generate this situation. Is it possible to have a dump of /proc/sched_debug before starting stress command ? to check if the problem is there from the beginning but not seen because not overloaded. Or if it the problem comes when user starts to load the system" -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1627108 Title: X1Carbon comes to a crawl during high CPU usage tasks To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1627108/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs