From 4d87ffadbba88105f33271bef5f2c79366c6a4e1 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Date: Wed, 4 Aug 2010 17:31:12 -0700 Subject: [PATCH] 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@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- init/Kconfig | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 79ac52bef4ce..dbc08baad77e 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -388,9 +388,12 @@ 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. -- GitLab