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[PATCH v4 1/4] sched: Define sched_clock_irqtime as static key

Yafang Shao posted 4 patches 1 year, 3 months ago
[PATCH v4 1/4] sched: Define sched_clock_irqtime as static key
Posted by Yafang Shao 1 year, 3 months ago 
Since CPU time accounting is a performance-critical path, let's define
sched_clock_irqtime as a static key to minimize potential overhead.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 kernel/sched/cputime.c | 16 +++++++---------
 kernel/sched/sched.h   |  1 +
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 0bed0fa1acd9..d0b6ea737d04 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -7,6 +7,8 @@
  #include <asm/cputime.h>
 #endif
 
+DEFINE_STATIC_KEY_FALSE(sched_clock_irqtime);
+
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
 
 /*
@@ -22,16 +24,14 @@
  */
 DEFINE_PER_CPU(struct irqtime, cpu_irqtime);
 
-static int sched_clock_irqtime;
-
 void enable_sched_clock_irqtime(void)
 {
-	sched_clock_irqtime = 1;
+	static_branch_enable(&sched_clock_irqtime);
 }
 
 void disable_sched_clock_irqtime(void)
 {
-	sched_clock_irqtime = 0;
+	static_branch_disable(&sched_clock_irqtime);
 }
 
 static void irqtime_account_delta(struct irqtime *irqtime, u64 delta,
@@ -57,7 +57,7 @@ void irqtime_account_irq(struct task_struct *curr, unsigned int offset)
 	s64 delta;
 	int cpu;
 
-	if (!sched_clock_irqtime)
+	if (!static_branch_likely(&sched_clock_irqtime))
 		return;
 
 	cpu = smp_processor_id();
@@ -90,8 +90,6 @@ static u64 irqtime_tick_accounted(u64 maxtime)
 
 #else /* CONFIG_IRQ_TIME_ACCOUNTING */
 
-#define sched_clock_irqtime	(0)
-
 static u64 irqtime_tick_accounted(u64 dummy)
 {
 	return 0;
@@ -478,7 +476,7 @@ void account_process_tick(struct task_struct *p, int user_tick)
 	if (vtime_accounting_enabled_this_cpu())
 		return;
 
-	if (sched_clock_irqtime) {
+	if (static_branch_likely(&sched_clock_irqtime)) {
 		irqtime_account_process_tick(p, user_tick, 1);
 		return;
 	}
@@ -507,7 +505,7 @@ void account_idle_ticks(unsigned long ticks)
 {
 	u64 cputime, steal;
 
-	if (sched_clock_irqtime) {
+	if (static_branch_likely(&sched_clock_irqtime)) {
 		irqtime_account_idle_ticks(ticks);
 		return;
 	}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 081519ffab46..038ce65d6635 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3179,6 +3179,7 @@ struct irqtime {
 };
 
 DECLARE_PER_CPU(struct irqtime, cpu_irqtime);
+DECLARE_STATIC_KEY_FALSE(sched_clock_irqtime);
 
 /*
  * Returns the irqtime minus the softirq time computed by ksoftirqd.
-- 
2.43.5
Re: [PATCH v4 1/4] sched: Define sched_clock_irqtime as static key
Posted by Peter Zijlstra 1 year, 3 months ago 
On Fri, Nov 01, 2024 at 11:17:47AM +0800, Yafang Shao wrote:
> Since CPU time accounting is a performance-critical path, let's define
> sched_clock_irqtime as a static key to minimize potential overhead.
> 
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> ---
>  kernel/sched/cputime.c | 16 +++++++---------
>  kernel/sched/sched.h   |  1 +
>  2 files changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index 0bed0fa1acd9..d0b6ea737d04 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -7,6 +7,8 @@
>   #include <asm/cputime.h>
>  #endif
>  
> +DEFINE_STATIC_KEY_FALSE(sched_clock_irqtime);
> +
>  #ifdef CONFIG_IRQ_TIME_ACCOUNTING
>  
>  /*
> @@ -22,16 +24,14 @@
>   */
>  DEFINE_PER_CPU(struct irqtime, cpu_irqtime);
>  
> -static int sched_clock_irqtime;
> -
>  void enable_sched_clock_irqtime(void)
>  {
> -	sched_clock_irqtime = 1;
> +	static_branch_enable(&sched_clock_irqtime);
>  }
>  
>  void disable_sched_clock_irqtime(void)
>  {
> -	sched_clock_irqtime = 0;
> +	static_branch_disable(&sched_clock_irqtime);
>  }
>  
>  static void irqtime_account_delta(struct irqtime *irqtime, u64 delta,
> @@ -57,7 +57,7 @@ void irqtime_account_irq(struct task_struct *curr, unsigned int offset)
>  	s64 delta;
>  	int cpu;
>  
> -	if (!sched_clock_irqtime)
> +	if (!static_branch_likely(&sched_clock_irqtime))
>  		return;
>  
>  	cpu = smp_processor_id();
> @@ -90,8 +90,6 @@ static u64 irqtime_tick_accounted(u64 maxtime)
>  
>  #else /* CONFIG_IRQ_TIME_ACCOUNTING */
>  
> -#define sched_clock_irqtime	(0)
> -
>  static u64 irqtime_tick_accounted(u64 dummy)
>  {
>  	return 0;

This makes no sense... in the IRQ_TIME_ACCOUNTING=n case you shouldn't
be using the static key.

> @@ -478,7 +476,7 @@ void account_process_tick(struct task_struct *p, int user_tick)
>  	if (vtime_accounting_enabled_this_cpu())
>  		return;
>  
> -	if (sched_clock_irqtime) {
> +	if (static_branch_likely(&sched_clock_irqtime)) {
>  		irqtime_account_process_tick(p, user_tick, 1);
>  		return;
>  	}
> @@ -507,7 +505,7 @@ void account_idle_ticks(unsigned long ticks)
>  {
>  	u64 cputime, steal;
>  
> -	if (sched_clock_irqtime) {
> +	if (static_branch_likely(&sched_clock_irqtime)) {
>  		irqtime_account_idle_ticks(ticks);
>  		return;
>  	}
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 081519ffab46..038ce65d6635 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -3179,6 +3179,7 @@ struct irqtime {
>  };
>  
>  DECLARE_PER_CPU(struct irqtime, cpu_irqtime);
> +DECLARE_STATIC_KEY_FALSE(sched_clock_irqtime);
>  
>  /*
>   * Returns the irqtime minus the softirq time computed by ksoftirqd.
> -- 
> 2.43.5
>
Re: [PATCH v4 1/4] sched: Define sched_clock_irqtime as static key
Posted by Yafang Shao 1 year, 3 months ago 
On Fri, Nov 1, 2024 at 6:06 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Nov 01, 2024 at 11:17:47AM +0800, Yafang Shao wrote:
> > Since CPU time accounting is a performance-critical path, let's define
> > sched_clock_irqtime as a static key to minimize potential overhead.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  kernel/sched/cputime.c | 16 +++++++---------
> >  kernel/sched/sched.h   |  1 +
> >  2 files changed, 8 insertions(+), 9 deletions(-)
> >
> > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> > index 0bed0fa1acd9..d0b6ea737d04 100644
> > --- a/kernel/sched/cputime.c
> > +++ b/kernel/sched/cputime.c
> > @@ -7,6 +7,8 @@
> >   #include <asm/cputime.h>
> >  #endif
> >
> > +DEFINE_STATIC_KEY_FALSE(sched_clock_irqtime);
> > +
> >  #ifdef CONFIG_IRQ_TIME_ACCOUNTING
> >
> >  /*
> > @@ -22,16 +24,14 @@
> >   */
> >  DEFINE_PER_CPU(struct irqtime, cpu_irqtime);
> >
> > -static int sched_clock_irqtime;
> > -
> >  void enable_sched_clock_irqtime(void)
> >  {
> > -     sched_clock_irqtime = 1;
> > +     static_branch_enable(&sched_clock_irqtime);
> >  }
> >
> >  void disable_sched_clock_irqtime(void)
> >  {
> > -     sched_clock_irqtime = 0;
> > +     static_branch_disable(&sched_clock_irqtime);
> >  }
> >
> >  static void irqtime_account_delta(struct irqtime *irqtime, u64 delta,
> > @@ -57,7 +57,7 @@ void irqtime_account_irq(struct task_struct *curr, unsigned int offset)
> >       s64 delta;
> >       int cpu;
> >
> > -     if (!sched_clock_irqtime)
> > +     if (!static_branch_likely(&sched_clock_irqtime))
> >               return;
> >
> >       cpu = smp_processor_id();
> > @@ -90,8 +90,6 @@ static u64 irqtime_tick_accounted(u64 maxtime)
> >
> >  #else /* CONFIG_IRQ_TIME_ACCOUNTING */
> >
> > -#define sched_clock_irqtime  (0)
> > -
> >  static u64 irqtime_tick_accounted(u64 dummy)
> >  {
> >       return 0;
>
> This makes no sense... in the IRQ_TIME_ACCOUNTING=n case you shouldn't
> be using the static key.

will change it.

-- 
Regards
Yafang

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