From ee968ac61d5a3440b931375d81113e0eedfcb249 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 31 Jul 2015 08:28:35 -0700 Subject: rcu: Eliminate panic when silly boot-time fanout specified This commit loosens rcutree.rcu_fanout_leaf range checks and replaces a panic() with a fallback to compile-time values. This fallback is accompanied by a WARN_ON(), and both occur when the rcutree.rcu_fanout_leaf value is too small to accommodate the number of CPUs. For example, given the current four-level limit for the rcu_node tree, a system with more than 16 CPUs built with CONFIG_FANOUT=2 must have rcutree.rcu_fanout_leaf larger than 2. Reported-by: Peter Zijlstra Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- Documentation/kernel-parameters.txt | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) (limited to 'Documentation') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 22a4b687ea5b..23ec96877311 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3074,9 +3074,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted. cache-to-cache transfer latencies. rcutree.rcu_fanout_leaf= [KNL] - Increase the number of CPUs assigned to each - leaf rcu_node structure. Useful for very large - systems. + Change the number of CPUs assigned to each + leaf rcu_node structure. Useful for very + large systems, which will choose the value 64, + and for NUMA systems with large remote-access + latencies, which will choose a value aligned + with the appropriate hardware boundaries. rcutree.jiffies_till_sched_qs= [KNL] Set required age in jiffies for a -- cgit v1.2.3