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rcu: Avoid waking up CPUs having only kfree_rcu() callbacks

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When CONFIG_RCU_FAST_NO_HZ is enabled, RCU will allow a given CPU to
enter dyntick-idle mode even if it still has RCU callbacks queued.
RCU avoids system hangs in this case by scheduling a timer for several
jiffies in the future.  However, if all of the callbacks on that CPU
are from kfree_rcu(), there is no reason to wake the CPU up, as it is
not a problem to defer freeing of memory.

This commit therefore tracks the number of callbacks on a given CPU
that are from kfree_rcu(), and avoids scheduling the timer if all of
a given CPU's callbacks are from kfree_rcu().

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2012-01-06 14:11:30 -08:00 • committed by Paul E. McKenney
commit 486e259340
10 changed files with 153 additions and 47 deletions
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2
include/linux/rcupdate.h
View file

@ -841,7 +841,7 @@ void __kfree_rcu(struct rcu_head *head, unsigned long offset)
/* See the kfree_rcu() header comment. */
BUILD_BUG_ON(!__is_kfree_rcu_offset(offset));
call_rcu(head, (rcu_callback)offset);
kfree_call_rcu(head, (rcu_callback)offset);
}
/**

6
include/linux/rcutiny.h
View file

@ -83,6 +83,12 @@ static inline void synchronize_sched_expedited(void)
synchronize_sched();
}
static inline void kfree_call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu))
{
call_rcu(head, func);
}
#ifdef CONFIG_TINY_RCU
static inline void rcu_preempt_note_context_switch(void)

2
include/linux/rcutree.h
View file

@ -61,6 +61,8 @@ extern void synchronize_rcu_bh(void);
extern void synchronize_sched_expedited(void);
extern void synchronize_rcu_expedited(void);
void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
static inline void synchronize_rcu_bh_expedited(void)
{
synchronize_sched_expedited();