linux-kernel - [PATCH tip/core/rcu 08/12] doc: Add rcutree.kthread

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Message-Id: <20190801223747.15560-8-paulmck@linux.ibm.com>
Date:   Thu,  1 Aug 2019 15:37:43 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 08/12] doc: Add rcutree.kthread_prio pointer to stallwarn.txt

This commit adds mention of the rcutree.kthread_prio kernel boot parameter
to the discussion of how high-priority real-time tasks can result in
RCU CPU stall warnings.  (However, this does not necessarily help when
the high-priority real-time tasks are using dubious deadlines.)

Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
 Documentation/RCU/stallwarn.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 13e88fc00f01..f48f4621ccbc 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -57,6 +57,12 @@ o	A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that
 	CONFIG_PREEMPT_RCU case, you might see stall-warning
 	messages.
 
+	You can use the rcutree.kthread_prio kernel boot parameter to
+	increase the scheduling priority of RCU's kthreads, which can
+	help avoid this problem.  However, please note that doing this
+	can increase your system's context-switch rate and thus degrade
+	performance.
+
 o	A periodic interrupt whose handler takes longer than the time
 	interval between successive pairs of interrupts.  This can
 	prevent RCU's kthreads and softirq handlers from running.
-- 
2.17.1