[PATCH v14 25/25] sched: use static key for sched_clock_running

Pavel Tatashin
2018-07-18T02:22:11Z

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>
---
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 7a8a63b940ee..858a1c8f594c 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();
}

@@ -204,7 +204,7 @@ void __init sched_clock_init(void)
{
unsigned long flags;

- sched_clock_running = 1;
+ static_branch_inc(&sched_clock_running);

/* Adjust __gtod_offset for contigious transition from early clock */
local_irq_save(flags);
@@ -218,7 +218,7 @@ 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.
*
@@ -363,7 +363,7 @@ 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();
@@ -386,7 +386,7 @@ 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();
@@ -445,13 +445,13 @@ 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