[PATCH 4/4] timers: Get this_cpu once while clearing idle timer

[Shrikanth Hegde]

Calling smp_processor_id() on:
- In CONFIG_DEBUG_PREEMPT=y, if preemption/irq is disabled, then it does
not print any warning.
- In CONFIG_DEBUG_PREEMPT=n, it doesn't do anything apart from getting
__smp_processor_id

So with both CONFIG_DEBUG_PREEMPT=y/n, in preemption disabled section
it is better to cache the value. It could save a few cycles. Though
tiny, repeated could add up to a small value.

timer_clear_idle is called with interrupts disabled.
So cache the value once.

Signed-off-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
---
 kernel/time/timer.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 7e1e3bde6b8b..04d928c21aba 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -2319,6 +2319,7 @@ u64 timer_base_try_to_set_idle(unsigned long basej, u64 basem, bool *idle)
  */
 void timer_clear_idle(void)
 {
+	int this_cpu = smp_processor_id();
 	/*
 	 * We do this unlocked. The worst outcome is a remote pinned timer
 	 * enqueue sending a pointless IPI, but taking the lock would just
@@ -2327,9 +2328,9 @@ void timer_clear_idle(void)
 	 * path. Required for BASE_LOCAL only.
 	 */
 	__this_cpu_write(timer_bases[BASE_LOCAL].is_idle, false);
-	if (tick_nohz_full_cpu(smp_processor_id()))
+	if (tick_nohz_full_cpu(this_cpu))
 		__this_cpu_write(timer_bases[BASE_GLOBAL].is_idle, false);
-	trace_timer_base_idle(false, smp_processor_id());
+	trace_timer_base_idle(false, this_cpu);
 
 	/* Activate without holding the timer_base->lock */
 	tmigr_cpu_activate();
-- 
2.47.3