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Commit 8a2ecf47 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
Browse files

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: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
Acked-by: default avatarDeepthi Dharwar <deepthi@linux.vnet.ibm.com>
parent 29e37d81

include/linux/rcupdate.h

+27 −0
Original line number Diff line number Diff line
@@ -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.

kernel/rcutiny.c

+2 −0
Original line number Diff line number Diff line
@@ -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.

kernel/rcutree.c

+2 −0
Original line number Diff line number Diff line
@@ -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