Messages in this thread | | | From | Joel Fernandes <> | Date | Fri, 5 Nov 2021 19:04:00 -0400 | Subject | Re: RT_GROUP_SCHED throttling blocks unthrottled RT tasks? |
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On Fri, Nov 5, 2021 at 1:44 PM Doug Anderson <dianders@chromium.org> wrote: [..] > > > I tried gathering some tracing. One bit that might (?) be relevant: > > cros_ec_spi_hig-179 [000] d.h5 1495.305919: sched_waking: > comm=kworker/4:2 pid=5232 prio=120 target_cpu=004 > cros_ec_spi_hig-179 [000] d.h6 1495.305926: sched_wakeup: > comm=kworker/4:2 pid=5232 prio=120 target_cpu=004 > <idle>-0 [001] d.H5 1495.309113: sched_waking: > comm=sugov:6 pid=2658 prio=-1 target_cpu=006 > <idle>-0 [001] d.H6 1495.309119: sched_wakeup: > comm=sugov:6 pid=2658 prio=-1 target_cpu=006 > cros_ec_spi_hig-179 [000] d.h5 1495.309336: sched_waking: > comm=sugov:6 pid=2658 prio=-1 target_cpu=006 > cros_ec_spi_hig-179 [000] d.h6 1495.309341: sched_wakeup: > comm=sugov:6 pid=2658 prio=-1 target_cpu=006 > <idle>-0 [001] d.H5 1495.312137: sched_waking: > comm=sugov:6 pid=2658 prio=-1 target_cpu=006 > <idle>-0 [001] d.H6 1495.312142: sched_wakeup: > comm=sugov:6 pid=2658 prio=-1 target_cpu=006 > cros_ec_spi_hig-179 [000] d.h5 1495.312859: sched_waking: > comm=sugov:6 pid=2658 prio=-1 target_cpu=006 > cros_ec_spi_hig-179 [000] d.h6 1495.312870: sched_wakeup: > comm=sugov:6 pid=2658 prio=-1 target_cpu=006 > > My best guess is that there's some bug in the scheduler where it just > loops constantly picking an unthrottled RT task but then incorrectly > decides that it's throttled and thus doesn't run it.
Thanks for posting this. Tricky bit indeed. I was wondering if the issue is here: https://elixir.bootlin.com/linux/latest/source/kernel/sched/rt.c#L1031
Basically, if something is actively getting RT-throttled on a CPU, then if something else unthrottled but RT is ready to run, the scheduler does resched_curr(rq) anyway. This probably happens when update_curr_rt() is called on the unthrottled RT task via task_tick_rt(). That seems a limitation of the current RT scheduler I think? Thoughts?
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