[PATCH v15 24/26] sched: use static key for sched_clock_running

[Pavel Tatashin]

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.tatas...@oracle.com>
Acked-by: Peter Zijlstra <pet...@infradead.org>
---
 kernel/sched/clock.c | 16 ++++++++--------
 kernel/sched/debug.c |  2 --
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index 422cd63f8f17..c5c47ad3f386 100644
--- a/kernel/sched/clock.c
+++ b/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();
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index e593b4118578..b0212f489a33 100644
--- a/kernel/sched/debug.c
+++ b/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);
-- 
2.18.0