sched/clock: Use static key for sched_clock_running

sched_clock_running may be read every time sched_clock_cpu() is called.
Yet, this variable is updated only twice during boot, and never changes
again, therefore it is better to make it a static key.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: steven.sistare@oracle.com
Cc: daniel.m.jordan@oracle.com
Cc: linux@armlinux.org.uk
Cc: schwidefsky@de.ibm.com
Cc: heiko.carstens@de.ibm.com
Cc: john.stultz@linaro.org
Cc: sboyd@codeaurora.org
Cc: hpa@zytor.com
Cc: douly.fnst@cn.fujitsu.com
Cc: prarit@redhat.com
Cc: feng.tang@intel.com
Cc: pmladek@suse.com
Cc: gnomes@lxorguk.ukuu.org.uk
Cc: linux-s390@vger.kernel.org
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: pbonzini@redhat.com
Link: https://lkml.kernel.org/r/20180719205545.16512-25-pasha.tatashin@oracle.com

kernel/sched/clock.c

@@ -67,7 +67,7 @@ unsigned long long __weak sched_clock(void)
 }
 EXPORT_SYMBOL_GPL(sched_clock);
 
-__read_mostly int sched_clock_running;
+static DEFINE_STATIC_KEY_FALSE(sched_clock_running);
 
 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
 /*
@@ -191,7 +191,7 @@ void clear_sched_clock_stable(void)
 
 	smp_mb(); /* matches sched_clock_init_late() */
 
-	if (sched_clock_running == 2)
+	if (static_key_count(&sched_clock_running.key) == 2)
 		__clear_sched_clock_stable();
 }
 
@@ -215,7 +215,7 @@ void __init sched_clock_init(void)
 	__sched_clock_gtod_offset();
 	local_irq_restore(flags);
 
-	sched_clock_running = 1;
+	static_branch_inc(&sched_clock_running);
 
 	/* Now that sched_clock_running is set adjust scd */
 	local_irq_save(flags);
@@ -228,7 +228,7 @@ void __init sched_clock_init(void)
  */
 static int __init sched_clock_init_late(void)
 {
-	sched_clock_running = 2;
+	static_branch_inc(&sched_clock_running);
 	/*
 	 * Ensure that it is impossible to not do a static_key update.
 	 *
@@ -373,7 +373,7 @@ u64 sched_clock_cpu(int cpu)
 	if (sched_clock_stable())
 		return sched_clock() + __sched_clock_offset;
 
-	if (unlikely(!sched_clock_running))
+	if (!static_branch_unlikely(&sched_clock_running))
 		return sched_clock();
 
 	preempt_disable_notrace();
@@ -396,7 +396,7 @@ void sched_clock_tick(void)
 	if (sched_clock_stable())
 		return;
 
-	if (unlikely(!sched_clock_running))
+	if (!static_branch_unlikely(&sched_clock_running))
 		return;
 
 	lockdep_assert_irqs_disabled();
@@ -455,13 +455,13 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
 
 void __init sched_clock_init(void)
 {
-	sched_clock_running = 1;
+	static_branch_inc(&sched_clock_running);
 	generic_sched_clock_init();
 }
 
 u64 sched_clock_cpu(int cpu)
 {
-	if (unlikely(!sched_clock_running))
+	if (!static_branch_unlikely(&sched_clock_running))
 		return 0;
 
 	return sched_clock();

kernel/sched/debug.c

@@ -623,8 +623,6 @@ void print_dl_rq(struct seq_file *m, int cpu, struct dl_rq *dl_rq)
 #undef PU
 }
 
-extern __read_mostly int sched_clock_running;
-
 static void print_cpu(struct seq_file *m, int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);