linux-kernel - [GIT pull] timer fixes for 3.15

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Date:	Thu, 17 Apr 2014 22:48:53 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [GIT pull] timer fixes for 3.15

Linus,

please pull the latest timers-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers-urgent-for-linus

Viresh unearthed the following three hickups in the timer/timekeeping
code:

- Negated check for the result of a clock event selection

- A missing early exit in the jiffies update path which causes
  update_wall_time to be called for nothing causing lock contention
  and wasted cycles in the timer interrupt

- Checking a variable in the NOHZ code enable code for true which can
  only be set by that very code after the check succeeds. That results
  in a rock solid runtime disablement of that feature.

Thanks,

	tglx

------------------>
Viresh Kumar (3):
      tick-common: Fix wrong check in tick_check_replacement()
      tick-sched: Don't call update_wall_time() when delta is lesser than tick_period
      tick-sched: Check tick_nohz_enabled in tick_nohz_switch_to_nohz()


 kernel/time/tick-common.c |    2 +-
 kernel/time/tick-sched.c  |    5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 0156612..0a0608e 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -276,7 +276,7 @@ static bool tick_check_preferred(struct clock_event_device *curdev,
 bool tick_check_replacement(struct clock_event_device *curdev,
 			    struct clock_event_device *newdev)
 {
-	if (tick_check_percpu(curdev, newdev, smp_processor_id()))
+	if (!tick_check_percpu(curdev, newdev, smp_processor_id()))
 		return false;
 
 	return tick_check_preferred(curdev, newdev);
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 9f8af69..6558b7a 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -84,6 +84,9 @@ static void tick_do_update_jiffies64(ktime_t now)
 
 		/* Keep the tick_next_period variable up to date */
 		tick_next_period = ktime_add(last_jiffies_update, tick_period);
+	} else {
+		write_sequnlock(&jiffies_lock);
+		return;
 	}
 	write_sequnlock(&jiffies_lock);
 	update_wall_time();
@@ -967,7 +970,7 @@ static void tick_nohz_switch_to_nohz(void)
 	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 	ktime_t next;
 
-	if (!tick_nohz_active)
+	if (!tick_nohz_enabled)
 		return;
 
 	local_irq_disable();
--
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