From 48d6a816a8bf36e2a197c322697323003bdc1cfe Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <fweisbec@gmail.com>
Date: Wed, 10 Jul 2013 02:44:35 +0200
Subject: [PATCH] context_tracking: Optimize guest APIs off case with static
 key

Optimize guest entry/exit APIs with static keys. This minimize
the overhead for those who enable CONFIG_NO_HZ_FULL without
always using it. Having no range passed to nohz_full= should
result in the probes overhead to be minimized.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Kevin Hilman <khilman@linaro.org>
---
 include/linux/context_tracking.h | 19 +++++++++++++++++--
 kernel/context_tracking.c        | 23 ++---------------------
 kernel/sched/cputime.c           |  2 ++
 3 files changed, 21 insertions(+), 23 deletions(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 38ab60b3f3a6..8854eadb2142 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -95,8 +95,23 @@ static inline void context_tracking_init(void) { }
 
 
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
-extern void guest_enter(void);
-extern void guest_exit(void);
+static inline void guest_enter(void)
+{
+	if (static_key_false(&context_tracking_enabled) &&
+	    vtime_accounting_enabled())
+		vtime_guest_enter(current);
+	else
+		current->flags |= PF_VCPU;
+}
+
+static inline void guest_exit(void)
+{
+	if (static_key_false(&context_tracking_enabled) &&
+	    vtime_accounting_enabled())
+		vtime_guest_exit(current);
+	else
+		current->flags &= ~PF_VCPU;
+}
 #else
 static inline void guest_enter(void)
 {
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 6e89e094c80e..b6a186c4b886 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -21,8 +21,10 @@
 #include <linux/export.h>
 
 struct static_key context_tracking_enabled = STATIC_KEY_INIT_FALSE;
+EXPORT_SYMBOL_GPL(context_tracking_enabled);
 
 DEFINE_PER_CPU(struct context_tracking, context_tracking);
+EXPORT_SYMBOL_GPL(context_tracking);
 
 void context_tracking_cpu_set(int cpu)
 {
@@ -163,27 +165,6 @@ void context_tracking_user_exit(void)
 	local_irq_restore(flags);
 }
 
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
-void guest_enter(void)
-{
-	if (vtime_accounting_enabled())
-		vtime_guest_enter(current);
-	else
-		current->flags |= PF_VCPU;
-}
-EXPORT_SYMBOL_GPL(guest_enter);
-
-void guest_exit(void)
-{
-	if (vtime_accounting_enabled())
-		vtime_guest_exit(current);
-	else
-		current->flags &= ~PF_VCPU;
-}
-EXPORT_SYMBOL_GPL(guest_exit);
-#endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */
-
-
 /**
  * context_tracking_task_switch - context switch the syscall callbacks
  * @prev: the task that is being switched out
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 223a35efa0a6..bb6b29a3067c 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -724,6 +724,7 @@ void vtime_guest_enter(struct task_struct *tsk)
 	current->flags |= PF_VCPU;
 	write_sequnlock(&tsk->vtime_seqlock);
 }
+EXPORT_SYMBOL_GPL(vtime_guest_enter);
 
 void vtime_guest_exit(struct task_struct *tsk)
 {
@@ -732,6 +733,7 @@ void vtime_guest_exit(struct task_struct *tsk)
 	current->flags &= ~PF_VCPU;
 	write_sequnlock(&tsk->vtime_seqlock);
 }
+EXPORT_SYMBOL_GPL(vtime_guest_exit);
 
 void vtime_account_idle(struct task_struct *tsk)
 {
-- 
2.20.1