diff options
| author | Paul E. McKenney <paulmck@kernel.org> | 2020-08-05 16:52:17 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2020-08-24 18:40:23 -0700 |
| commit | dc1269186bed3afc5a2018527516be84fe55d3e0 (patch) | |
| tree | 60ef8b9f467c3cbdda1655f840c96346527080ab /kernel/rcu/Kconfig | |
| parent | 8cbd0e38a9f2de38e8991c5c1c6f9024b2731d17 (diff) | |
rcu: Reduce leaf fanout for strict RCU grace periods
Because strict RCU grace periods will complete more quickly, they will
experience greater lock contention on each leaf rcu_node structure's
->lock. This commit therefore reduces the leaf fanout in order to reduce
this lock contention.
Note that this also has the effect of reducing the number of CPUs
supported to 16 in the case of CONFIG_RCU_FANOUT_LEAF=2 or 81 in the
case of CONFIG_RCU_FANOUT_LEAF=3. However, greater numbers of CPUs are
probably a bad idea when using CONFIG_RCU_STRICT_GRACE_PERIOD=y. Those
wishing to live dangerously are free to edit their kernel/rcu/Kconfig
files accordingly.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu/Kconfig')
| -rw-r--r-- | kernel/rcu/Kconfig | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index 0ebe15a84985..b71e21f73c40 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -135,10 +135,12 @@ config RCU_FANOUT config RCU_FANOUT_LEAF int "Tree-based hierarchical RCU leaf-level fanout value" - range 2 64 if 64BIT - range 2 32 if !64BIT + range 2 64 if 64BIT && !RCU_STRICT_GRACE_PERIOD + range 2 32 if !64BIT && !RCU_STRICT_GRACE_PERIOD + range 2 3 if RCU_STRICT_GRACE_PERIOD depends on TREE_RCU && RCU_EXPERT - default 16 + default 16 if !RCU_STRICT_GRACE_PERIOD + default 2 if RCU_STRICT_GRACE_PERIOD help This option controls the leaf-level fanout of hierarchical implementations of RCU, and allows trading off cache misses |