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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>
This commit is contained in:
Frederic Weisbecker 2013-07-11 19:42:13 +02:00
parent 48d6a816a8
commit 73d424f9af
2 changed files with 12 additions and 5 deletions
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11
include/linux/context_tracking.h
View File

@ -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) { }
@ -112,6 +118,7 @@ static inline void guest_exit(void)
else
current->flags &= ~PF_VCPU;
}
#else
static inline void guest_enter(void)
{

6
kernel/context_tracking.c
View File

@ -166,7 +166,7 @@ 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
*
@ -178,8 +178,8 @@ 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);