linux-kernel - [PATCH 10/18] context_tracking: Optimize context switch off case with static keys

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Date:	Wed, 17 Jul 2013 18:44:23 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	Kevin Hilman <khilman@...aro.org>
Subject: [PATCH 10/18] context_tracking: Optimize context switch off case with static keys

No need for syscall slowpath if no CPU is full dynticks,
rather nop this in this case.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Li Zhong <zhong@...ux.vnet.ibm.com>
Cc: Mike Galbraith <efault@....de>
Cc: Kevin Hilman <khilman@...aro.org>
---
 include/linux/context_tracking.h |   11 +++++++++--
 kernel/context_tracking.c        |    6 +++---
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 8eba58c..77f7306 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -40,6 +40,8 @@ extern void context_tracking_cpu_set(int cpu);
 
 extern void context_tracking_user_enter(void);
 extern void context_tracking_user_exit(void);
+extern void __context_tracking_task_switch(struct task_struct *prev,
+					   struct task_struct *next);
 
 static inline void user_enter(void)
 {
@@ -74,8 +76,12 @@ static inline void exception_exit(enum ctx_state prev_ctx)
 	}
 }
 
-extern void context_tracking_task_switch(struct task_struct *prev,
-					 struct task_struct *next);
+static inline void context_tracking_task_switch(struct task_struct *prev,
+						struct task_struct *next)
+{
+	if (static_key_false(&context_tracking_enabled))
+		__context_tracking_task_switch(prev, next);
+}
 #else
 static inline bool context_tracking_in_user(void) { return false; }
 static inline void user_enter(void) { }
@@ -104,6 +110,7 @@ static inline void guest_exit(void)
 	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 7b0a22d..5323a5c 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -164,7 +164,7 @@ void context_tracking_user_exit(void)
 }
 
 /**
- * context_tracking_task_switch - context switch the syscall callbacks
+ * __context_tracking_task_switch - context switch the syscall callbacks
  * @prev: the task that is being switched out
  * @next: the task that is being switched in
  *
@@ -176,8 +176,8 @@ void context_tracking_user_exit(void)
  * migrate to some CPU that doesn't do the context tracking. As such the TIF
  * flag may not be desired there.
  */
-void context_tracking_task_switch(struct task_struct *prev,
-			     struct task_struct *next)
+void __context_tracking_task_switch(struct task_struct *prev,
+				    struct task_struct *next)
 {
 	clear_tsk_thread_flag(prev, TIF_NOHZ);
 	set_tsk_thread_flag(next, TIF_NOHZ);
-- 
1.7.5.4

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