Commit 89f7f291 authored by Paul E. McKenney's avatar Paul E. McKenney
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doc: Document rcutree.nocb_nobypass_lim_per_jiffy kernel parameter 



This commit provides documentation for the kernel parameter controlling
RCU's handling of callback floods on offloaded (rcu_nocbs) CPUs.
This parameter might be obscure, but it is always there when you need it.

Reported-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Reported-by: default avatarUladzislau Rezki <urezki@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Reviewed-by: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
parent 71de1e34

Documentation/admin-guide/kernel-parameters.txt

+13 −0
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@@ -4681,6 +4681,19 @@ 
			invoked in the context of an rcuoc kthread, which

			scheduler will preempt as it does any other task.



	rcutree.nocb_nobypass_lim_per_jiffy= [KNL]

			On callback-offloaded (rcu_nocbs) CPUs,

			RCU reduces the lock contention that would

			otherwise be caused by callback floods through

			use of the ->nocb_bypass list.	However, in the

			common non-flooded case, RCU queues directly to

			the main ->cblist in order to avoid the extra

			overhead of the ->nocb_bypass list and its lock.

			But if there are too many callbacks queued during

			a single jiffy, RCU pre-queues the callbacks into

			the ->nocb_bypass queue.  The definition of "too

			many" is supplied by this kernel boot parameter.



	rcutree.rcu_nocb_gp_stride= [KNL]

			Set the number of NOCB callback kthreads in

			each group, which defaults to the square root