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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-06-26 17:00:35 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-09-23 07:41:54 -0700
commit394f2769aa0dbcf027bae6fb52835e25e05d332e (patch)
tree78471127d379e8d128d73e976ce33022c195b0c5 /kernel/rcutree.h
parent4605c0143c6d611b3076025ba3a7e04293c01d69 (diff)
downloadop-kernel-dev-394f2769aa0dbcf027bae6fb52835e25e05d332e.zip
op-kernel-dev-394f2769aa0dbcf027bae6fb52835e25e05d332e.tar.gz
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 <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'kernel/rcutree.h')
-rw-r--r--kernel/rcutree.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 7fb93ce..8f0293c 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -202,6 +202,7 @@ struct rcu_node {
/* per-CPU kthreads as needed. */
unsigned int node_kthread_status;
/* State of node_kthread_task for tracing. */
+ raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
} ____cacheline_internodealigned_in_smp;
/*
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