linux-kernel - [PATCH tip/core/rcu 07/10] rcu: Fix RCU

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Date:	Mon,  9 Aug 2010 15:15:08 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 07/10] rcu: Fix RCU_FANOUT help message

Commit cf244dc01bf68 added a fourth level to the TREE_RCU hierarchy,
but the RCU_FANOUT help message still said "cube root".  This commit
fixes this to "fourth root" and also emphasizes that production
systems are well-served by the default.  (Stress-testing RCU itself
uses small RCU_FANOUT values in order to test large-system code paths
on small(er) systems.)

Located-by: John Kacur <jkacur@...hat.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 init/Kconfig |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 9366954..7faa5d8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -384,9 +384,12 @@ config RCU_FANOUT
 	help
 	  This option controls the fanout of hierarchical implementations
 	  of RCU, allowing RCU to work efficiently on machines with
-	  large numbers of CPUs.  This value must be at least the cube
-	  root of NR_CPUS, which allows NR_CPUS up to 32,768 for 32-bit
-	  systems and up to 262,144 for 64-bit systems.
+	  large numbers of CPUs.  This value must be at least the fourth
+	  root of NR_CPUS, which allows NR_CPUS to be insanely large.
+	  The default value of RCU_FANOUT should be used for production
+	  systems, but if you are stress-testing the RCU implementation
+	  itself, small RCU_FANOUT values allow you to test large-system
+	  code paths on small(er) systems.
 
 	  Select a specific number if testing RCU itself.
 	  Take the default if unsure.
-- 
1.7.0.6

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