From: Paul E. McKenney Date: Wed, 27 Jun 2012 00:00:35 +0000 (-0700) Subject: rcu: Prevent force_quiescent_state() memory contention X-Git-Tag: omap-for-v3.7-rc1/fixes-cpufreq-signed~101^2~1^2~13 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=394f2769aa0dbcf027bae6fb52835e25e05d332e;p=pandora-kernel.git rcu: Prevent force_quiescent_state() memory contention Large systems running RCU_FAST_NO_HZ kernels see extreme memory contention on the rcu_state structure's ->fqslock field. This can be avoided by disabling RCU_FAST_NO_HZ, either at compile time or at boot time (via the nohz kernel boot parameter), but large systems will no doubt become sensitive to energy consumption. This commit therefore uses a combining-tree approach to spread the memory contention across new cache lines in the leaf rcu_node structures. This can be thought of as a tournament lock that has only a try-lock acquisition primitive. The effect on small systems is minimal, because such systems have an rcu_node "tree" consisting of a single node. In addition, this functionality is not used on fastpaths. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- Reading git-diff-tree failed