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Subject[patch 1/2] tick/broadcast: Prevent deep idle states if no broadcast device available
If no broadcast device is installed and the cpu local timers stop in
deeper idle states, then there is currently nothing telling the idle
code that it should not go into deep idle states, so the timers stop
and nothing wakes up the cpus.

Make the broadcast_enter/exit() functions independent of the
configuration options and always check on enter:

- whether the cpu local device is affected by idle states
- whether a broadcast device is available

This covers all possible config combinations including
CONFIG_BROADCAST=n.

Reported-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Suzuki Poulose <Suzuki.Poulose@arm.com>
Cc: Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

---
include/linux/tick.h | 4 -
kernel/time/tick-broadcast.c | 97 +++++++++++++++++++++++++------------------
kernel/time/tick-common.c | 21 +++++++++
kernel/time/tick-sched.h | 10 ++++
4 files changed, 88 insertions(+), 44 deletions(-)

Index: tip/include/linux/tick.h
===================================================================
--- tip.orig/include/linux/tick.h
+++ tip/include/linux/tick.h
@@ -63,11 +63,7 @@ extern void tick_broadcast_control(enum
static inline void tick_broadcast_control(enum tick_broadcast_mode mode) { }
#endif /* BROADCAST */

-#if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT)
extern int tick_broadcast_oneshot_control(enum tick_broadcast_state state);
-#else
-static inline int tick_broadcast_oneshot_control(enum tick_broadcast_state state) { return 0; }
-#endif

static inline void tick_broadcast_enable(void)
{
Index: tip/kernel/time/tick-broadcast.c
===================================================================
--- tip.orig/kernel/time/tick-broadcast.c
+++ tip/kernel/time/tick-broadcast.c
@@ -359,7 +359,14 @@ void tick_broadcast_control(enum tick_br
case TICK_BROADCAST_ON:
cpumask_set_cpu(cpu, tick_broadcast_on);
if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_mask)) {
- if (tick_broadcast_device.mode ==
+ /*
+ * Only shutdown the cpu local device, if the
+ * broadcast device exists and is in periodic
+ * mode. The latter check prevents a hickup
+ * during the switch from periodic to oneshot
+ * mode.
+ */
+ if (bc != NULL && tick_broadcast_device.mode ==
TICKDEV_MODE_PERIODIC)
clockevents_shutdown(dev);
}
@@ -662,46 +669,43 @@ static void broadcast_shutdown_local(str
clockevents_switch_state(dev, CLOCK_EVT_STATE_SHUTDOWN);
}

-/**
- * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode
- * @state: The target state (enter/exit)
- *
- * The system enters/leaves a state, where affected devices might stop
- * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.
- *
- * Called with interrupts disabled, so clockevents_lock is not
- * required here because the local clock event device cannot go away
- * under us.
- */
-int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
+int __tick_broadcast_oneshot_control(enum tick_broadcast_state state)
{
struct clock_event_device *bc, *dev;
- struct tick_device *td;
int cpu, ret = 0;
ktime_t now;

/*
- * Periodic mode does not care about the enter/exit of power
- * states
+ * If there is no broadcast device, tell the caller not to go
+ * into deep idle.
*/
- if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
- return 0;
-
- /*
- * We are called with preemtion disabled from the depth of the
- * idle code, so we can't be moved away.
- */
- td = this_cpu_ptr(&tick_cpu_device);
- dev = td->evtdev;
+ if (!tick_broadcast_device.evtdev)
+ return -EBUSY;

- if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
- return 0;
+ dev = this_cpu_ptr(&tick_cpu_device)->evtdev;

raw_spin_lock(&tick_broadcast_lock);
bc = tick_broadcast_device.evtdev;
cpu = smp_processor_id();

if (state == TICK_BROADCAST_ENTER) {
+ /*
+ * If the current CPU owns the hrtimer broadcast
+ * mechanism, it cannot go deep idle and we do not add
+ * the CPU to the broadcast mask. We don't have to go
+ * through the EXIT path as the local timer is not
+ * shutdown.
+ */
+ ret = broadcast_needs_cpu(bc, cpu);
+
+ /*
+ * If the hrtimer broadcast check tells us that the
+ * cpu cannot go deep idle, or if the broadcast device
+ * is in periodic mode, we just return.
+ */
+ if (ret || tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
+ goto out;
+
if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_oneshot_mask)) {
WARN_ON_ONCE(cpumask_test_cpu(cpu, tick_broadcast_pending_mask));
broadcast_shutdown_local(bc, dev);
@@ -711,22 +715,28 @@ int tick_broadcast_oneshot_control(enum
* if the cpu local event is earlier than the
* broadcast event. If the current CPU is in
* the force mask, then we are going to be
- * woken by the IPI right away.
+ * woken by the IPI right away; we return
+ * busy, so the CPU does not try to go deep
+ * idle.
*/
- if (!cpumask_test_cpu(cpu, tick_broadcast_force_mask) &&
- dev->next_event.tv64 < bc->next_event.tv64)
+ if (cpumask_test_cpu(cpu, tick_broadcast_force_mask)) {
+ ret = -EBUSY;
+ } else if (dev->next_event.tv64 < bc->next_event.tv64) {
tick_broadcast_set_event(bc, cpu, dev->next_event);
+ /*
+ * In case of hrtimer broadcasts the
+ * programming might have moved the
+ * timer to this cpu. If yes, remove
+ * us from the broadcast mask and
+ * return busy.
+ */
+ ret = broadcast_needs_cpu(bc, cpu);
+ if (ret) {
+ cpumask_clear_cpu(cpu,
+ tick_broadcast_oneshot_mask);
+ }
+ }
}
- /*
- * If the current CPU owns the hrtimer broadcast
- * mechanism, it cannot go deep idle and we remove the
- * CPU from the broadcast mask. We don't have to go
- * through the EXIT path as the local timer is not
- * shutdown.
- */
- ret = broadcast_needs_cpu(bc, cpu);
- if (ret)
- cpumask_clear_cpu(cpu, tick_broadcast_oneshot_mask);
} else {
if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_oneshot_mask)) {
clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);
@@ -938,6 +948,13 @@ bool tick_broadcast_oneshot_available(vo
return bc ? bc->features & CLOCK_EVT_FEAT_ONESHOT : false;
}

+#else
+int __tick_broadcast_oneshot_control(enum tick_broadcast_state state)
+{
+ if (!tick_broadcast_device.evtdev)
+ return -EBUSY;
+ return 0;
+}
#endif

void __init tick_broadcast_init(void)
Index: tip/kernel/time/tick-common.c
===================================================================
--- tip.orig/kernel/time/tick-common.c
+++ tip/kernel/time/tick-common.c
@@ -342,6 +342,27 @@ out_bc:
tick_install_broadcast_device(newdev);
}

+/**
+ * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode
+ * @state: The target state (enter/exit)
+ *
+ * The system enters/leaves a state, where affected devices might stop
+ * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.
+ *
+ * Called with interrupts disabled, so clockevents_lock is not
+ * required here because the local clock event device cannot go away
+ * under us.
+ */
+int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
+{
+ struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
+
+ if (!(td->evtdev->features & CLOCK_EVT_FEAT_C3STOP))
+ return 0;
+
+ return __tick_broadcast_oneshot_control(state);
+}
+
#ifdef CONFIG_HOTPLUG_CPU
/*
* Transfer the do_timer job away from a dying cpu.
Index: tip/kernel/time/tick-sched.h
===================================================================
--- tip.orig/kernel/time/tick-sched.h
+++ tip/kernel/time/tick-sched.h
@@ -71,4 +71,14 @@ extern void tick_cancel_sched_timer(int
static inline void tick_cancel_sched_timer(int cpu) { }
#endif

+#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
+extern int __tick_broadcast_oneshot_control(enum tick_broadcast_state state);
+#else
+static inline int
+__tick_broadcast_oneshot_control(enum tick_broadcast_state state)
+{
+ return -EBUSY;
+}
+#endif
+
#endif



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