[PATCH 09/23] context_tracking: Optimize guest APIs off case with static key

From: Frederic Weisbecker
Date: Wed Jul 31 2013 - 20:32:09 EST


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@xxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Kevin Hilman <khilman@xxxxxxxxxx>
---
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 e5ec0c9..03a32b0 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -87,8 +87,23 @@ static inline void context_tracking_task_switch(struct task_struct *prev,
#endif /* !CONFIG_CONTEXT_TRACKING */

#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 657f668..5afa36b 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 223a35e..bb6b29a 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)
{
--
1.7.5.4

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