From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Wed, 9 May 2012 04:00:28 +0000 (-0700)
Subject: rcu: Size rcu_node tree from nr_cpu_ids rather than NR_CPUS
X-Git-Tag: v3.6-rc1~168^2^2~17
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cca6f3931920a7547d02e68adc2ca635bea5600c;p=pandora-kernel.git

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>
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