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From: Paul E. McKenney on 9 Aug 2010 18:20
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(a)redhat.com>
Signed-off-by: Paul E. McKenney <paulmck(a)linux.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
@@ -384,9 +384,12 @@ config RCU_FANOUT
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.
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