linux-kernel - [PATCH tip/core/rcu 1/6] documentation: Fix relation between nohz_full and rcu

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Date:   Mon, 24 Jul 2017 14:36:23 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     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,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 1/6] documentation: Fix relation between nohz_full and rcu_nocbs

If a CPU is specified in the nohz_full= kernel boot parameter to a
kernel built with CONFIG_NO_HZ_FULL=y, then that CPU's callbacks will
be offloaded, just as if that CPU had also been specified in the
rcu_nocbs= kernel boot parameter.  But the current documentation
states that the user must keep these two boot parameters manually
synchronized.  This commit therefore updates the documentation to
reflect reality.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index d9c171ce4190..3a99cc96b6b1 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2633,9 +2633,10 @@
 			In kernels built with CONFIG_NO_HZ_FULL=y, set
 			the specified list of CPUs whose tick will be stopped
 			whenever possible. The boot CPU will be forced outside
-			the range to maintain the timekeeping.
-			The CPUs in this range must also be included in the
-			rcu_nocbs= set.
+			the range to maintain the timekeeping.  Any CPUs
+			in this list will have their RCU callbacks offloaded,
+			just as if they had also been called out in the
+			rcu_nocbs= boot parameter.
 
 	noiotrap	[SH] Disables trapped I/O port accesses.
 
-- 
2.5.2