Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 04/13] rcu: Make RCU_FANOUT_LEAF help text more explicit about skew_tick | Date | Wed, 12 Apr 2017 09:55:40 -0700 |
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If you set RCU_FANOUT_LEAF too high, you can get lock contention on the leaf rcu_node, and you should boot with the skew_tick kernel parameter set in order to avoid this lock contention. This commit therefore upgrades the RCU_FANOUT_LEAF help text to explicitly state this.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- init/Kconfig | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/init/Kconfig b/init/Kconfig index a92f27da4a27..946e561e67b7 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -612,11 +612,17 @@ config RCU_FANOUT_LEAF 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. + leaf-level fanouts work well. That said, setting leaf-level + fanout to a large number will likely cause problematic + lock contention on the leaf-level rcu_node structures unless + you boot with the skew_tick kernel parameter. Select a specific number if testing RCU itself. - Select the maximum permissible value for large systems. + Select the maximum permissible value for large systems, but + please understand that you may also need to set the + skew_tick kernel boot parameter to avoid contention + on the rcu_node structure's locks. Take the default if unsure. -- 2.5.2
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