When a CPU has to enter an idle state where tick stops, it makes a call
to tick_broadcast_enter(). The call will fail if this CPU is the
broadcast CPU. Today, under such a circumstance, the arch cpuidle code
handles this CPU.  This is not convincing because not only do we not
know what the arch cpuidle code does, but we also do not account for the
idle state residency time and usage of such a CPU.

This scenario can be handled better by simply choosing an idle state
where in ticks do not stop. To accommodate this change move the setting
of runqueue idle state from the core to the cpuidle driver, else the
rq->idle_state will be set wrong.

Signed-off-by: Preeti U Murthy <redacted>
---
Changes from V2: https://lkml.org/lkml/2015/5/7/78
Introduce a function in cpuidle core to select an idle state where ticks do not
stop rather than going through the governors.

Changes from V1: https://lkml.org/lkml/2015/5/7/24
Rebased on the latest linux-pm/bleeding-edge branch

 drivers/cpuidle/cpuidle.c |   45 +++++++++++++++++++++++++++++++++++++++++++--
 include/linux/sched.h     |   16 ++++++++++++++++
 kernel/sched/core.c       |   17 +++++++++++++++++
 kernel/sched/fair.c       |    2 +-
 kernel/sched/idle.c       |    6 ------
 kernel/sched/sched.h      |   24 ------------------------
 6 files changed, 77 insertions(+), 33 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 8c24f95..d1af760 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c

@@ -21,6 +21,7 @@
 #include <linux/module.h>
 #include <linux/suspend.h>
 #include <linux/tick.h>
+#include <linux/sched.h>
 #include <trace/events/power.h>
 
 #include "cpuidle.h"

@@ -146,6 +147,36 @@ int cpuidle_enter_freeze(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	return index;
 }
 
+/*
+ * find_tick_valid_state - select a state where tick does not stop
+ * @dev: cpuidle device for this cpu
+ * @drv: cpuidle driver for this cpu
+ */
+static int find_tick_valid_state(struct cpuidle_device *dev,
+				struct cpuidle_driver *drv)
+{
+	int i, ret = -1;
+
+	for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
+		struct cpuidle_state *s = &drv->states[i];
+		struct cpuidle_state_usage *su = &dev->states_usage[i];
+
+		/*
+		 * We do not explicitly check for latency requirement
+		 * since it is safe to assume that only shallower idle
+		 * states will have the CPUIDLE_FLAG_TIMER_STOP bit
+		 * cleared and they will invariably meet the latency
+		 * requirement.
+		 */
+		if (s->disabled || su->disable ||
+			(s->flags & CPUIDLE_FLAG_TIMER_STOP))
+			continue;
+
+		ret = i;
+	}
+	return ret;
+}
+
 /**
  * cpuidle_enter_state - enter the state and update stats
  * @dev: cpuidle device for this cpu

@@ -168,10 +199,17 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
 	 * CPU as a broadcast timer, this call may fail if it is not available.
 	 */
 	if (broadcast && tick_broadcast_enter()) {
-		default_idle_call();
-		return -EBUSY;
+		index = find_tick_valid_state(dev, drv);