doc: Document the rcutree.rcu_divisor kernel boot parameter

This commit adds kernel-parameters.txt documentation for the
rcutree.rcu_divisor kernel boot parameter, which controls the softirq
callback-invocation batch limit.

Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2522b11..bdf431b 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4666,6 +4666,21 @@
                        When RCU_NOCB_CPU is set, also adjust the
                        priority of NOCB callback kthreads.
 
+       rcutree.rcu_divisor= [KNL]
+                       Set the shift-right count to use to compute
+                       the callback-invocation batch limit bl from
+                       the number of callbacks queued on this CPU.
+                       The result will be bounded below by the value of
+                       the rcutree.blimit kernel parameter.  Every bl
+                       callbacks, the softirq handler will exit in
+                       order to allow the CPU to do other work.
+
+                       Please note that this callback-invocation batch
+                       limit applies only to non-offloaded callback
+                       invocation.  Offloaded callbacks are instead
+                       invoked in the context of an rcuoc kthread, which
+                       scheduler will preempt as it does any other task.
+
        rcutree.rcu_nocb_gp_stride= [KNL]
                        Set the number of NOCB callback kthreads in
                        each group, which defaults to the square root