Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/linux-2.6-hrt

* 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/linux-2.6-hrt:
  NOHZ: reevaluate idle sleep length after add_timer_on()
  clocksource: revert: use init_timer_deferrable for clocksource_watchdog

4 files changed, 59 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index fed07d03364e..6a1e7afb099b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1541,6 +1541,12 @@ static inline void idle_task_exit(void) {}
 
 extern void sched_idle_next(void);
 
+#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
+extern void wake_up_idle_cpu(int cpu);
+#else
+static inline void wake_up_idle_cpu(int cpu) { }
+#endif
+
 #ifdef CONFIG_SCHED_DEBUG
 extern unsigned int sysctl_sched_latency;
 extern unsigned int sysctl_sched_min_granularity;
diff --git a/kernel/sched.c b/kernel/sched.c
index 28c73f07efb2..8dcdec6fe0fe 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1052,6 +1052,49 @@ static void resched_cpu(int cpu)
 	resched_task(cpu_curr(cpu));
 	spin_unlock_irqrestore(&rq->lock, flags);
 }
+
+#ifdef CONFIG_NO_HZ
+/*
+ * When add_timer_on() enqueues a timer into the timer wheel of an
+ * idle CPU then this timer might expire before the next timer event
+ * which is scheduled to wake up that CPU. In case of a completely
+ * idle system the next event might even be infinite time into the
+ * future. wake_up_idle_cpu() ensures that the CPU is woken up and
+ * leaves the inner idle loop so the newly added timer is taken into
+ * account when the CPU goes back to idle and evaluates the timer
+ * wheel for the next timer event.
+ */
+void wake_up_idle_cpu(int cpu)
+{
+	struct rq *rq = cpu_rq(cpu);
+
+	if (cpu == smp_processor_id())
+		return;
+
+	/*
+	 * This is safe, as this function is called with the timer
+	 * wheel base lock of (cpu) held. When the CPU is on the way
+	 * to idle and has not yet set rq->curr to idle then it will
+	 * be serialized on the timer wheel base lock and take the new
+	 * timer into account automatically.
+	 */
+	if (rq->curr != rq->idle)
+		return;
+
+	/*
+	 * We can set TIF_RESCHED on the idle task of the other CPU
+	 * lockless. The worst case is that the other CPU runs the
+	 * idle task through an additional NOOP schedule()
+	 */
+	set_tsk_thread_flag(rq->idle, TIF_NEED_RESCHED);
+
+	/* NEED_RESCHED must be visible before we test polling */
+	smp_mb();
+	if (!tsk_is_polling(rq->idle))
+		smp_send_reschedule(cpu);
+}
+#endif
+
 #else
 static void __resched_task(struct task_struct *p, int tif_bit)
 {
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 278534bbca95..7f60097d443a 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -174,7 +174,7 @@ static void clocksource_check_watchdog(struct clocksource *cs)
 			if (watchdog)
 				del_timer(&watchdog_timer);
 			watchdog = cs;
-			init_timer_deferrable(&watchdog_timer);
+			init_timer(&watchdog_timer);
 			watchdog_timer.function = clocksource_watchdog;
 
 			/* Reset watchdog cycles */
diff --git a/kernel/timer.c b/kernel/timer.c
index 99b00a25f88b..b024106daa70 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -451,10 +451,18 @@ void add_timer_on(struct timer_list *timer, int cpu)
 	spin_lock_irqsave(&base->lock, flags);
 	timer_set_base(timer, base);
 	internal_add_timer(base, timer);
+	/*
+	 * Check whether the other CPU is idle and needs to be
+	 * triggered to reevaluate the timer wheel when nohz is
+	 * active. We are protected against the other CPU fiddling
+	 * with the timer by holding the timer base lock. This also
+	 * makes sure that a CPU on the way to idle can not evaluate
+	 * the timer wheel.
+	 */
+	wake_up_idle_cpu(cpu);
 	spin_unlock_irqrestore(&base->lock, flags);
 }
 
-
 /**
  * mod_timer - modify a timer's timeout
  * @timer: the timer to be modified