Commit-ID: 8a2ecf474d3ee8dd5d001490349e422cec52f39f
Gitweb: http://git.kernel.org/tip/8a2ecf474d3ee8dd5d001490349e422cec52f39f
Author: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
AuthorDate: Thu, 2 Feb 2012 15:42:04 -0800
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue, 21 Feb 2012 09:06:13 -0800
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@xxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Acked-by: Deepthi Dharwar <deepthi@xxxxxxxxxxxxxxxxxx>
---
include/linux/rcupdate.h | 27 +++++++++++++++++++++++++++
kernel/rcutiny.c | 2 ++
kernel/rcutree.c | 2 ++
3 files changed, 31 insertions(+), 0 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 6ee663c..9372174 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -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.
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index c8b0e15..37a5444 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -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.
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 92b4776..eacc10b 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -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
--
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