tree 6e278a9ee7a72eb642c7d8d19900fce454c3960d
parent 58d96ffa1d1e788ffee9aaac3106732c80e75f25
author Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1336536028 -0700
committer Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1337621634 -0700

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>