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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2012-05-08 21:00:28 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2012-07-02 12:33:21 -0700 |
| commit | cca6f3931920a7547d02e68adc2ca635bea5600c (patch) | |
| tree | 31e2cd3d9e73f080ca78a89a6dba474c1987beee /kernel | |
| parent | cc5df65b0370fc6aa2bfe3bb19e0451d5cafb99f (diff) | |
| download | lwn-cca6f3931920a7547d02e68adc2ca635bea5600c.tar.gz lwn-cca6f3931920a7547d02e68adc2ca635bea5600c.zip | |
rcu: Size rcu_node tree from nr_cpu_ids rather than NR_CPUS
The rcu_node tree array is sized based on compile-time constants,
including NR_CPUS. Although this approach has worked well in the past,
the recent trend by many distros to define NR_CPUS=4096 results in
excessive grace-period-initialization latencies.
This commit therefore substitutes the run-time computed nr_cpu_ids for
the compile-time NR_CPUS when building the tree. This can result in
much of the compile-time-allocated rcu_node array being unused. If
this is a major problem, you are in a specialized situation anyway,
so you can manually adjust the NR_CPUS, RCU_FANOUT, and RCU_FANOUT_LEAF
kernel config parameters.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/rcutree.c | 2 | ||||
| -rw-r--r-- | kernel/rcutree_plugin.h | 2 |
2 files changed, 3 insertions, 1 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index a4c592b66e10..0fdbc5e07302 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2675,7 +2675,7 @@ static void __init rcu_init_geometry(void) { int i; int j; - int n = NR_CPUS; + int n = nr_cpu_ids; int rcu_capacity[MAX_RCU_LVLS + 1]; /* If the compile-time values are accurate, just leave. */ diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 70e0fd256cc6..ef2b5231afa4 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -72,6 +72,8 @@ static void __init rcu_bootup_announce_oddness(void) #endif if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF) printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); + if (nr_cpu_ids != NR_CPUS) + printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); } #ifdef CONFIG_TREE_PREEMPT_RCU |