From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
peterz@infradead.org, rostedt@goodmis.org,
Valdis.Kletnieks@vt.edu, dhowells@redhat.com,
eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com,
patches@linaro.org, "Paul E. McKenney" <paul.mckenney@linaro.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH RFC tip/core/rcu 2/3] rcu: Add RCU_NONIDLE() for idle-loop RCU read-side critical sections
Date: Thu, 2 Feb 2012 17:12:47 -0800 [thread overview]
Message-ID: <1328231568-2971-2-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <1328231568-2971-1-git-send-email-paulmck@linux.vnet.ibm.com>
From: "Paul E. McKenney" <paul.mckenney@linaro.org>
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>
---
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 5098aea..b4142a9 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 e81298a..25111d3 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
--
1.7.8
next prev parent reply other threads:[~2012-02-03 1:13 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-03 1:12 [PATCH RFC 0/3] Fix cpuidle_idle_call() RCU usage Paul E. McKenney
2012-02-03 1:12 ` [PATCH RFC tip/core/rcu 1/3] rcu: Allow nesting of rcu_idle_enter() and rcu_idle_exit() Paul E. McKenney
2012-02-03 1:12 ` Paul E. McKenney [this message]
2012-02-03 1:12 ` [PATCH RFC tip/core/rcu 3/3] cpuidle: Inform RCU of read-side critical sections Paul E. McKenney
2012-02-03 11:02 ` Deepthi Dharwar
2012-02-03 2:43 ` [PATCH RFC 0/3] Fix cpuidle_idle_call() RCU usage Josh Triplett
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