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SubjectFalse-positive RCU stall warnings on large systems...
Hi Paul,

On some of our larger servers with many hundreds of cores and when under
high duress, we can see scheduler RCU stall warnings [1], so find we
have to increase the hardcoded RCU_STALL_RAT_DELAY up from 2 and
RCU_JIFFIES_TILL_FORCE_QS up from 3.

Is there a more sustainable way to account for this to avoid it being
hard-coded, such as making it and dependent timeouts a fraction of
CONFIG_RCU_CPU_STALL_TIMEOUT?

On the other hand, perhaps this is just caused by clock jitter (eg due
to distance from a contended clock source)? So increasing these a bit
may just be adequate in general...

Many thanks,
Daniel

--- [1]

[ 3939.010085] INFO: rcu_sched detected stalls on CPUs/tasks: {}
(detected by 1, t=29662 jiffies, g=3053, c=3052, q=598)
[ 3939.020008] INFO: Stall ended before state dump start
--
Daniel J Blueman
Principal Software Engineer, Numascale Asia


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