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rcu: Move PREEMPT_RCU preemption to switch_to() invocation

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Currently, PREEMPT_RCU readers are enqueued upon entry to the scheduler.
This is inefficient because enqueuing is required only if there is a
context switch, and entry to the scheduler does not guarantee a context
switch.

The commit therefore moves the enqueuing to immediately precede the
call to switch_to() from the scheduler.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Paul E. McKenney
2012-03-27 16:02:08 -07:00
committed by Paul E. McKenney
parent 66f75a5d02
commit 616c310e83
8 changed files with 16 additions and 19 deletions
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6
include/linux/rcutiny.h
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@@ -87,10 +87,6 @@ static inline void kfree_call_rcu(struct rcu_head *head,
#ifdef CONFIG_TINY_RCU
static inline void rcu_preempt_note_context_switch(void)
{
}
static inline void exit_rcu(void)
{
}
@@ -102,7 +98,6 @@ static inline int rcu_needs_cpu(int cpu)
#else /* #ifdef CONFIG_TINY_RCU */
void rcu_preempt_note_context_switch(void);
extern void exit_rcu(void);
int rcu_preempt_needs_cpu(void);
@@ -116,7 +111,6 @@ static inline int rcu_needs_cpu(int cpu)
static inline void rcu_note_context_switch(int cpu)
{
rcu_sched_qs(cpu);
rcu_preempt_note_context_switch();
}
/*