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@linux.ibm.com>

diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 13e88fc00f01aaca0039701377737a94e583f615..f48f4621ccbc2b261e6e9e924ca19b9f508c02a5 100644 (file)
--- 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.