diff options
| -rw-r--r-- | Documentation/kernel-parameters.txt | 9 | ||||
| -rw-r--r-- | kernel/rcu/tree.c | 20 |
2 files changed, 17 insertions, 12 deletions
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 diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 93c0f23c3e45..713eb92314b4 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4230,13 +4230,12 @@ static void __init rcu_init_geometry(void) rcu_fanout_leaf, nr_cpu_ids); /* - * The boot-time rcu_fanout_leaf parameter is only permitted - * to increase the leaf-level fanout, not decrease it. Of course, - * the leaf-level fanout cannot exceed the number of bits in - * the rcu_node masks. Complain and fall back to the compile- - * time values if these limits are exceeded. + * The boot-time rcu_fanout_leaf parameter must be at least two + * and cannot exceed the number of bits in the rcu_node masks. + * Complain and fall back to the compile-time values if this + * limit is exceeded. */ - if (rcu_fanout_leaf < RCU_FANOUT_LEAF || + if (rcu_fanout_leaf < 2 || rcu_fanout_leaf > sizeof(unsigned long) * 8) { rcu_fanout_leaf = RCU_FANOUT_LEAF; WARN_ON(1); @@ -4253,10 +4252,13 @@ static void __init rcu_init_geometry(void) /* * The tree must be able to accommodate the configured number of CPUs. - * If this limit is exceeded than we have a serious problem elsewhere. + * If this limit is exceeded, fall back to the compile-time values. */ - if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) - panic("rcu_init_geometry: rcu_capacity[] is too small"); + if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) { + rcu_fanout_leaf = RCU_FANOUT_LEAF; + WARN_ON(1); + return; + } /* Calculate the number of levels in the tree. */ for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) { |