linux-kernel - [PATCH tip/core/rcu 2/3] rcu: provide rcu_virt_note_context

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Date:	Sun,  8 May 2011 06:34:09 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	patches@...aro.org, Gleb Natapov <gleb@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 2/3] rcu: provide rcu_virt_note_context_switch() function.

From: Gleb Natapov <gleb@...hat.com>

Provide rcu_virt_note_context_switch() for vitalization use to note
quiescent state during guest entry.

Signed-off-by: Gleb Natapov <gleb@...hat.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/linux/rcutiny.h |    8 ++++++++
 include/linux/rcutree.h |   10 ++++++++++
 kernel/rcutree.c        |    1 +
 3 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 30ebd7c..52b3e02 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -100,6 +100,14 @@ static inline void rcu_note_context_switch(int cpu)
 }
 
 /*
+ * Take advantage of the fact that there is only one CPU, which
+ * allows us to ignore virtualization-based context switches.
+ */
+static inline void rcu_virt_note_context_switch(int cpu)
+{
+}
+
+/*
  * Return the number of grace periods.
  */
 static inline long rcu_batches_completed(void)
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 284dad1..e65d066 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -35,6 +35,16 @@ extern void rcu_note_context_switch(int cpu);
 extern int rcu_needs_cpu(int cpu);
 extern void rcu_cpu_stall_reset(void);
 
+/*
+ * Note a virtualization-based context switch.  This is simply a
+ * wrapper around rcu_note_context_switch(), which allows TINY_RCU
+ * to save a few bytes.
+ */
+static inline void rcu_virt_note_context_switch(int cpu)
+{
+	rcu_note_context_switch(cpu);
+}
+
 #ifdef CONFIG_TREE_PREEMPT_RCU
 
 extern void exit_rcu(void);
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index b2fe2a2..54ff7eb 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -157,6 +157,7 @@ void rcu_note_context_switch(int cpu)
 	rcu_sched_qs(cpu);
 	rcu_preempt_note_context_switch(cpu);
 }
+EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
 #ifdef CONFIG_NO_HZ
 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
-- 
1.7.3.2

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