rcu: Prevent force_quiescent_state() memory contention

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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>

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This commit is contained in:

Paul E. McKenney 2012-06-26 17:00:35 -07:00

parent 4605c0143c

commit 394f2769aa

2 changed files with 38 additions and 10 deletions

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47

kernel/rcutree.c

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1

kernel/rcutree.h

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