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rcu: Add RCU_NONIDLE() for idle-loop RCU read-side critical sections 

RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
in the inner idle loop, that is, between the rcu_idle_enter() and the
rcu_idle_exit() -- RCU will happily ignore any such read-side critical
sections.  However, things like powertop need tracepoints in the inner
idle loop.

This commit therefore provides an RCU_NONIDLE() macro that can be used to
wrap code in the idle loop that requires RCU read-side critical sections.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2012-02-02 15:42:04 -08:00 committed by Paul E. McKenney
parent 29e37d8141
commit 8a2ecf474d
3 changed files with 31 additions and 0 deletions
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27
include/linux/rcupdate.h
View File

@ -190,6 +190,33 @@ extern void rcu_idle_exit(void);
extern void rcu_irq_enter(void);
extern void rcu_irq_exit(void);
/**
* RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
* @a: Code that RCU needs to pay attention to.
*
* RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
* in the inner idle loop, that is, between the rcu_idle_enter() and
* the rcu_idle_exit() -- RCU will happily ignore any such read-side
* critical sections. However, things like powertop need tracepoints
* in the inner idle loop.
*
* This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
* will tell RCU that it needs to pay attending, invoke its argument
* (in this example, a call to the do_something_with_RCU() function),
* and then tell RCU to go back to ignoring this CPU. It is permissible
* to nest RCU_NONIDLE() wrappers, but the nesting level is currently
* quite limited. If deeper nesting is required, it will be necessary
* to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
*
* This macro may be used from process-level code only.
*/
#define RCU_NONIDLE(a) \
do { \
rcu_idle_exit(); \
do { a; } while (0); \
rcu_idle_enter(); \
} while (0)
/*
* Infrastructure to implement the synchronize_() primitives in
* TREE_RCU and rcu_barrier_() primitives in TINY_RCU.

2
kernel/rcutiny.c
View File

@ -97,6 +97,7 @@ void rcu_idle_enter(void)
rcu_idle_enter_common(oldval);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_enter);
/*
* Exit an interrupt handler towards idle.
@ -153,6 +154,7 @@ void rcu_idle_exit(void)
rcu_idle_exit_common(oldval);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_exit);
/*
* Enter an interrupt handler, moving away from idle.

2
kernel/rcutree.c
View File

@ -402,6 +402,7 @@ void rcu_idle_enter(void)
rcu_idle_enter_common(rdtp, oldval);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_enter);
/**
* rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
@ -493,6 +494,7 @@ void rcu_idle_exit(void)
rcu_idle_exit_common(rdtp, oldval);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_exit);
/**
* rcu_irq_enter - inform RCU that current CPU is entering irq away from idle