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@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>
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 8854ead..e070ea5 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -40,6 +40,8 @@
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 @@
}
}
-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) { }
@@ -112,6 +118,7 @@
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 b6a186c..c178226 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -166,7 +166,7 @@
}
/**
- * 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
*
@@ -178,8 +178,8 @@
* 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);