linux-kernel - [PATCH rcu 2/3] doc: Document the rcutree.rcu

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Message-Id: <20220620221757.3839212-2-paulmck@kernel.org>
Date:   Mon, 20 Jun 2022 15:17:56 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH rcu 2/3] 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@...gle.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 Documentation/admin-guide/kernel-parameters.txt | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2522b11e593f2..bdf431bdbfdc4 100644
--- 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
-- 
2.31.1.189.g2e36527f23