rcu/nocb: Reduce contention at no-CBs registry-time CB advancement

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Currently, __call_rcu_nocb_wake() conditionally acquires the leaf rcu_node
structure's ->lock, and only afterwards does rcu_advance_cbs_nowake()
check to see if it is possible to advance callbacks without potentially
needing to awaken the grace-period kthread.  Given that the no-awaken
check can be done locklessly, this commit reverses the order, so that
rcu_advance_cbs_nowake() is invoked without holding the leaf rcu_node
structure's ->lock and rcu_advance_cbs_nowake() checks the grace-period
state before conditionally acquiring that lock, thus reducing the number
of needless acquistions of the leaf rcu_node structure's ->lock.

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

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Paul E. McKenney 2019-06-01 06:16:38 -07:00

parent 9fcb09bddd

commit 6608c3a027

2 changed files with 4 additions and 5 deletions

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5

kernel/rcu/tree.c

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4

kernel/rcu/tree_plugin.h

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