Diffstat (limited to 'init')
1 files changed, 27 insertions, 0 deletions
diff --git a/init/Kconfig b/init/Kconfig
index 85c6870ed476..6d18ef8071b5 100644
@@ -458,6 +458,33 @@ config RCU_FANOUT
Select a specific number if testing RCU itself.
Take the default if unsure.
+ int "Tree-based hierarchical RCU leaf-level fanout value"
+ range 2 RCU_FANOUT if 64BIT
+ range 2 RCU_FANOUT if !64BIT
+ depends on TREE_RCU || TREE_PREEMPT_RCU
+ default 16
+ This option controls the leaf-level fanout of hierarchical
+ implementations of RCU, and allows trading off cache misses
+ against lock contention. Systems that synchronize their
+ scheduling-clock interrupts for energy-efficiency reasons will
+ want the default because the smaller leaf-level fanout keeps
+ lock contention levels acceptably low. Very large systems
+ (hundreds or thousands of CPUs) will instead want to set this
+ value to the maximum value possible in order to reduce the
+ number of cache misses incurred during RCU's grace-period
+ initialization. These systems tend to run CPU-bound, and thus
+ are not helped by synchronized interrupts, and thus tend to
+ skew them, which reduces lock contention enough that large
+ leaf-level fanouts work well.
+ Select a specific number if testing RCU itself.
+ Select the maximum permissible value for large systems.
+ Take the default if unsure.
bool "Disable tree-based hierarchical RCU auto-balancing"
depends on TREE_RCU || TREE_PREEMPT_RCU