linux-kernel - [tip: sched/core] sched: Define sched_clock

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Message-ID: <173693263486.31546.10051301284393438661.tip-bot2@tip-bot2>
Date: Wed, 15 Jan 2025 09:17:14 -0000
From: "tip-bot2 for Yafang Shao" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Yafang Shao <laoar.shao@...il.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, mkoutny@...e.com,
 Vincent Guittot <vincent.guittot@...aro.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched: Define sched_clock_irqtime as static key

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     8722903cbb8f0d51057fbf9ef1c680756b74119e
Gitweb:        https://git.kernel.org/tip/8722903cbb8f0d51057fbf9ef1c680756b74119e
Author:        Yafang Shao <laoar.shao@...il.com>
AuthorDate:    Fri, 03 Jan 2025 10:24:06 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 13 Jan 2025 14:10:25 +01:00

sched: Define sched_clock_irqtime as static key

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@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Michal Koutný <mkoutny@...e.com>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Link: https://lore.kernel.org/r/20250103022409.2544-2-laoar.shao@gmail.com
---
 kernel/sched/cputime.c | 16 +++++++---------
 kernel/sched/sched.h   | 13 +++++++++++++
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 0bed0fa..5d9143d 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -9,6 +9,8 @@
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
 
+DEFINE_STATIC_KEY_FALSE(sched_clock_irqtime);
+
 /*
  * There are no locks covering percpu hardirq/softirq time.
  * They are only modified in vtime_account, on corresponding CPU
@@ -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 (!irqtime_enabled())
 		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 (irqtime_enabled()) {
 		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 (irqtime_enabled()) {
 		irqtime_account_idle_ticks(ticks);
 		return;
 	}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 300db6f..3da237c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3233,6 +3233,12 @@ struct irqtime {
 };
 
 DECLARE_PER_CPU(struct irqtime, cpu_irqtime);
+DECLARE_STATIC_KEY_FALSE(sched_clock_irqtime);
+
+static inline int irqtime_enabled(void)
+{
+	return static_branch_likely(&sched_clock_irqtime);
+}
 
 /*
  * Returns the irqtime minus the softirq time computed by ksoftirqd.
@@ -3253,6 +3259,13 @@ static inline u64 irq_time_read(int cpu)
 	return total;
 }
 
+#else
+
+static inline int irqtime_enabled(void)
+{
+	return 0;
+}
+
 #endif /* CONFIG_IRQ_TIME_ACCOUNTING */
 
 #ifdef CONFIG_CPU_FREQ