From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Wed, 15 Dec 2010 00:07:52 +0000 (-0800)
Subject: rcu: limit rcu_node leaf-level fanout
X-Git-Tag: v2.6.38-rc1~492^2^2~3
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0209f6490b030f35349a2bb71294f3fd75b0f36d;p=pandora-kernel.git

rcu: limit rcu_node leaf-level fanout

Some recent benchmarks have indicated possible lock contention on the
leaf-level rcu_node locks.  This commit therefore limits the number of
CPUs per leaf-level rcu_node structure to 16, in other words, there
can be at most 16 rcu_data structures fanning into a given rcu_node
structure.  Prior to this, the limit was 32 on 32-bit systems and 64 on
64-bit systems.

Note that the fanout of non-leaf rcu_node structures is unchanged.  The
organization of accesses to the rcu_node tree is such that references
to non-leaf rcu_node structures are much less frequent than to the
leaf structures.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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