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That did make it easier :-) >>>>>>>>> >>>>>>>>> Here is what I see ... >>>>>>>> >>>>>>>> Thanks! >>>>>>>> >>>>>>>> Still different from what I can repro over here, so, unfortunately, I >>>>>>>> had to add additional debug printks. Pushed to the same branch/repo. >>>>>>>> >>>>>>>> Could I ask for another run with it? Please also share the complete >>>>>>>> dmesg from boot, as I would need to check debug output when CPUs are >>>>>>>> first onlined. >>>>>> >>>>>> So you have a system with 2 big and 4 LITTLE CPUs (Denver0 Denver1 A57_0 >>>>>> A57_1 A57_2 A57_3) in one MC sched domain and (Denver1 and A57_0) are >>>>>> isol CPUs? >>>>> >>>>> I believe that 1-2 are the denvers (even thought they are listed as 0-1 in device-tree). >>>> >>>> Interesting, I have yet to reproduce this with equal capacities in isolcpus. >>>> Maybe I didn't try hard enough yet. >>>> >>>>> >>>>>> This should be easy to set up for me on my Juno-r0 [A53 A57 A57 A53 A53 A53] >>>>> >>>>> Yes I think it is similar to this. >>>>> >>>>> Thanks! >>>>> Jon >>>>> >>>> >>>> I could reproduce that on a different LLLLbb with isolcpus=3,4 (Lb) and >>>> the offlining order: >>>> echo 0 > /sys/devices/system/cpu/cpu5/online >>>> echo 0 > /sys/devices/system/cpu/cpu1/online >>>> echo 0 > /sys/devices/system/cpu/cpu3/online >>>> echo 0 > /sys/devices/system/cpu/cpu2/online >>>> echo 0 > /sys/devices/system/cpu/cpu4/online >>>> >>>> while the following offlining order succeeds: >>>> echo 0 > /sys/devices/system/cpu/cpu5/online >>>> echo 0 > /sys/devices/system/cpu/cpu4/online >>>> echo 0 > /sys/devices/system/cpu/cpu1/online >>>> echo 0 > /sys/devices/system/cpu/cpu2/online >>>> echo 0 > /sys/devices/system/cpu/cpu3/online >>>> (Both offline an isolcpus last, both have CPU0 online) >>>> >>>> The issue only triggers with sugov DL threads (I guess that's obvious, but >>>> just to mention it). >>> >>> It wasn't obvious to me at first :). So thanks for confirming. >>> >>>> I'll investigate some more later but wanted to share for now. >>> >>> So, problem actually is that I am not yet sure what we should do with >>> sugovs' bandwidth wrt root domain accounting. W/o isolation it's all >>> good, as it gets accounted for correctly on the dynamic domains sugov >>> tasks can run on. But with isolation and sugov affected_cpus that cross >>> isolation domains (e.g., one BIG one little), we can get into troubles >>> not knowing if sugov contribution should fall on the DEF or DYN domain. >>> >>> Hummm, need to think more about it. >> >> That is indeed tricky. >> I would've found it super appealing to always just have sugov DL tasks activate >> on this_cpu and not have to worry about all this, but then you have contention >> amongst CPUs of a cluster and there are energy improvements from always >> having little cores handle all sugov DL tasks, even for the big CPUs, >> that's why I introduced >> commit 93940fbdc468 ("cpufreq/schedutil: Only bind threads if needed") >> but that really doesn't make this any easier. > > What about we actually ignore them consistently? We already do that for > admission control, so maybe we can do that when rebuilding domains as > well (until we find maybe a better way to deal with them). > > Does the following make any difference? > > --- > kernel/sched/deadline.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index b254d878789d..8f7420e0c9d6 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -2995,7 +2995,7 @@ void dl_add_task_root_domain(struct task_struct *p) > struct dl_bw *dl_b; > > raw_spin_lock_irqsave(&p->pi_lock, rf.flags); > - if (!dl_task(p)) { > + if (!dl_task(p) || dl_entity_is_special(&p->dl)) { > raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags); > return; > } > I have tested this on top of v6.14-rc2, but this is still not resolving the issue for me :-( Jon -- nvpublic