[PATCH V2 0/2] time/cpuidle: Support in tick broadcast framework in absence of external clock device

[PATCH V2 0/2] time/cpuidle: Support in tick broadcast framework in absence of external clock device

[Preeti U Murthy]

This earlier version of this patchset can be found here:
https://lkml.org/lkml/2013/12/12/687. This version has been based on the
discussion in http://www.kernelhub.org/?p=2&msg=399516.

This patchset provides the hooks that the architectures without an external
clock device and deep idle states where the local timers stop can make use of.

Presently we are in need of this support on certain implementations of
PowerPC. This patchset has been used on PowerPC for testing with

---

Preeti U Murthy (1):
      time: Change the return type of clockevents_notify() to integer

Thomas Gleixner (1):
      tick/cpuidle: Initialize hrtimer mode of broadcast


 include/linux/clockchips.h           |   15 ++++-
 kernel/time/Makefile                 |    2 -
 kernel/time/clockevents.c            |    8 ++-
 kernel/time/tick-broadcast-hrtimer.c |  102 ++++++++++++++++++++++++++++++++++
 kernel/time/tick-broadcast.c         |   51 ++++++++++++++++-
 kernel/time/tick-internal.h          |    6 +-
 6 files changed, 171 insertions(+), 13 deletions(-)
 create mode 100644 kernel/time/tick-broadcast-hrtimer.c

-- 

[PATCH V2 1/2] time: Change the return type of clockevents_notify() to integer

[Preeti U Murthy]

The broadcast framework can potentially be made use of by archs which do not have an
external clock device as well. Then, it is required that one of the CPUs need
to handle the broadcasting of wakeup IPIs to the CPUs in deep idle. As a
result its local timers should remain functional all the time. For such
a CPU, the BROADCAST_ENTER notification has to fail indicating that its clock
device cannot be shutdown. To make way for this support, change the return
type of tick_broadcast_oneshot_control() and hence clockevents_notify() to
indicate such scenarios.

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
---

 include/linux/clockchips.h   |    6 +++---
 kernel/time/clockevents.c    |    8 +++++---
 kernel/time/tick-broadcast.c |    6 ++++--
 kernel/time/tick-internal.h  |    6 +++---
 4 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index 493aa02..ac81b56 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -186,9 +186,9 @@ static inline int tick_check_broadcast_expired(void) { return 0; }
 #endif
 
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
-extern void clockevents_notify(unsigned long reason, void *arg);
+extern int clockevents_notify(unsigned long reason, void *arg);
 #else
-static inline void clockevents_notify(unsigned long reason, void *arg) {}
+static inline int clockevents_notify(unsigned long reason, void *arg) {}
 #endif
 
 #else /* CONFIG_GENERIC_CLOCKEVENTS_BUILD */
@@ -196,7 +196,7 @@ static inline void clockevents_notify(unsigned long reason, void *arg) {}
 static inline void clockevents_suspend(void) {}
 static inline void clockevents_resume(void) {}
 
-static inline void clockevents_notify(unsigned long reason, void *arg) {}
+static inline int clockevents_notify(unsigned long reason, void *arg) {}
 static inline int tick_check_broadcast_expired(void) { return 0; }
 
 #endif
diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 086ad60..79b8685 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -524,12 +524,13 @@ void clockevents_resume(void)
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
 /**
  * clockevents_notify - notification about relevant events
+ * Returns 0 on success, any other value on error
  */
-void clockevents_notify(unsigned long reason, void *arg)
+int clockevents_notify(unsigned long reason, void *arg)
 {
 	struct clock_event_device *dev, *tmp;
 	unsigned long flags;
-	int cpu;
+	int cpu, ret = 0;
 
 	raw_spin_lock_irqsave(&clockevents_lock, flags);
 
@@ -542,7 +543,7 @@ void clockevents_notify(unsigned long reason, void *arg)
 
 	case CLOCK_EVT_NOTIFY_BROADCAST_ENTER:
 	case CLOCK_EVT_NOTIFY_BROADCAST_EXIT:
-		tick_broadcast_oneshot_control(reason);
+		ret = tick_broadcast_oneshot_control(reason);
 		break;
 
 	case CLOCK_EVT_NOTIFY_CPU_DYING:
@@ -585,6 +586,7 @@ void clockevents_notify(unsigned long reason, void *arg)
 		break;
 	}
 	raw_spin_unlock_irqrestore(&clockevents_lock, flags);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(clockevents_notify);
 
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 9532690..be00692 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -633,14 +633,15 @@ again:
 /*
  * Powerstate information: The system enters/leaves a state, where
  * affected devices might stop
+ * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.
  */
-void tick_broadcast_oneshot_control(unsigned long reason)
+int tick_broadcast_oneshot_control(unsigned long reason)
 {
 	struct clock_event_device *bc, *dev;
 	struct tick_device *td;
 	unsigned long flags;
 	ktime_t now;
-	int cpu;
+	int cpu, ret = 0;
 
 	/*
 	 * Periodic mode does not care about the enter/exit of power
@@ -746,6 +747,7 @@ void tick_broadcast_oneshot_control(unsigned long reason)
 	}
 out:
 	raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
+	return ret;
 }
 
 /*
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 18e71f7..164465c 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -46,7 +46,7 @@ extern int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *));
 extern void tick_resume_oneshot(void);
 # ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
 extern void tick_broadcast_setup_oneshot(struct clock_event_device *bc);
-extern void tick_broadcast_oneshot_control(unsigned long reason);
+extern int tick_broadcast_oneshot_control(unsigned long reason);
 extern void tick_broadcast_switch_to_oneshot(void);
 extern void tick_shutdown_broadcast_oneshot(unsigned int *cpup);
 extern int tick_resume_broadcast_oneshot(struct clock_event_device *bc);
@@ -58,7 +58,7 @@ static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
 {
 	BUG();
 }
-static inline void tick_broadcast_oneshot_control(unsigned long reason) { }
+static inline int tick_broadcast_oneshot_control(unsigned long reason) { }
 static inline void tick_broadcast_switch_to_oneshot(void) { }
 static inline void tick_shutdown_broadcast_oneshot(unsigned int *cpup) { }
 static inline int tick_broadcast_oneshot_active(void) { return 0; }
@@ -87,7 +87,7 @@ static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
 {
 	BUG();
 }
-static inline void tick_broadcast_oneshot_control(unsigned long reason) { }
+static inline int tick_broadcast_oneshot_control(unsigned long reason) { }
 static inline void tick_shutdown_broadcast_oneshot(unsigned int *cpup) { }
 static inline int tick_resume_broadcast_oneshot(struct clock_event_device *bc)
 {

Re: [PATCH V2 1/2] time: Change the return type of clockevents_notify() to integer

[Thomas Gleixner]

On Fri, 24 Jan 2014, Preeti U Murthy wrote:
> -extern void tick_broadcast_oneshot_control(unsigned long reason);
> +extern int tick_broadcast_oneshot_control(unsigned long reason);

> -static inline void tick_broadcast_oneshot_control(unsigned long reason) { }
> +static inline int tick_broadcast_oneshot_control(unsigned long reason) { }

> -static inline void tick_broadcast_oneshot_control(unsigned long reason) { }
> +static inline int tick_broadcast_oneshot_control(unsigned long reason) { }

The inline stubs need to return 0.

Thanks,

	tglx

Re: [PATCH V2 1/2] time: Change the return type of clockevents_notify() to integer

[Preeti U Murthy]

On 02/04/2014 03:31 PM, Thomas Gleixner wrote:
> On Fri, 24 Jan 2014, Preeti U Murthy wrote:
>> -extern void tick_broadcast_oneshot_control(unsigned long reason);
>> +extern int tick_broadcast_oneshot_control(unsigned long reason);
> 
>> -static inline void tick_broadcast_oneshot_control(unsigned long reason) { }
>> +static inline int tick_broadcast_oneshot_control(unsigned long reason) { }
> 
>> -static inline void tick_broadcast_oneshot_control(unsigned long reason) { }
>> +static inline int tick_broadcast_oneshot_control(unsigned long reason) { }
> 
> The inline stubs need to return 0.

Oh right! Apologies!
Thanks.
> 
> Thanks,
> 
> 	tglx
> 

Regards
Preeti U Murthy

[PATCH V2 2/2] tick/cpuidle: Initialize hrtimer mode of broadcast

[Preeti U Murthy]

From: Thomas Gleixner <tglx@linutronix.de>

On some architectures, in certain CPU deep idle states the local timers stop.
An external clock device is used to wakeup these CPUs. The kernel support for the
wakeup of these CPUs is provided by the tick broadcast framework by using the
external clock device as the wakeup source.

However not all implementations of architectures provide such an external
clock device. This patch includes support in the broadcast framework to handle
the wakeup of the CPUs in deep idle states on such systems by queuing a hrtimer
on one of the CPUs, which is meant to handle the wakeup of CPUs in deep idle states.

This patchset introduces a pseudo clock device which can be registered by the
archs as tick_broadcast_device in the absence of a real external clock
device. Once registered, the broadcast framework will work as is for these
architectures as long as the archs take care of the BROADCAST_ENTER
notification failing for one of the CPUs. This CPU is made the stand by CPU to
handle wakeup of the CPUs in deep idle and it *must not enter deep idle states*.

The CPU with the earliest wakeup is chosen to be this CPU. Hence this way the
stand by CPU dynamically moves around and so does the hrtimer which is queued
to trigger at the next earliest wakeup time. This is consistent with the case where
an external clock device is present. The smp affinity of this clock device is
set to the CPU with the earliest wakeup. This patchset handles the hotplug of
the stand by CPU as well by moving the hrtimer on to the CPU handling the CPU_DEAD
notification.

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
[Added Changelog and code to handle reprogramming of hrtimer]
---

 include/linux/clockchips.h           |    9 +++
 kernel/time/Makefile                 |    2 -
 kernel/time/tick-broadcast-hrtimer.c |  102 ++++++++++++++++++++++++++++++++++
 kernel/time/tick-broadcast.c         |   45 +++++++++++++++
 4 files changed, 156 insertions(+), 2 deletions(-)
 create mode 100644 kernel/time/tick-broadcast-hrtimer.c

diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index ac81b56..2293025 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -62,6 +62,11 @@ enum clock_event_mode {
 #define CLOCK_EVT_FEAT_DYNIRQ		0x000020
 #define CLOCK_EVT_FEAT_PERCPU		0x000040
 
+/*
+ * Clockevent device is based on a hrtimer for broadcast
+ */
+#define CLOCK_EVT_FEAT_HRTIMER		0x000080
+
 /**
  * struct clock_event_device - clock event device descriptor
  * @event_handler:	Assigned by the framework to be called by the low
@@ -83,6 +88,7 @@ enum clock_event_mode {
  * @name:		ptr to clock event name
  * @rating:		variable to rate clock event devices
  * @irq:		IRQ number (only for non CPU local devices)
+ * @bound_on:		Bound on CPU
  * @cpumask:		cpumask to indicate for which CPUs this device works
  * @list:		list head for the management code
  * @owner:		module reference
@@ -113,6 +119,7 @@ struct clock_event_device {
 	const char		*name;
 	int			rating;
 	int			irq;
+	int			bound_on;
 	const struct cpumask	*cpumask;
 	struct list_head	list;
 	struct module		*owner;
@@ -180,9 +187,11 @@ extern int tick_receive_broadcast(void);
 #endif
 
 #if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT)
+extern void tick_setup_hrtimer_broadcast(void);
 extern int tick_check_broadcast_expired(void);
 #else
 static inline int tick_check_broadcast_expired(void) { return 0; }
+static void tick_setup_hrtimer_broadcast(void) {};
 #endif
 
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index 9250130..06151ef 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -3,7 +3,7 @@ obj-y += timeconv.o posix-clock.o alarmtimer.o
 
 obj-$(CONFIG_GENERIC_CLOCKEVENTS_BUILD)		+= clockevents.o
 obj-$(CONFIG_GENERIC_CLOCKEVENTS)		+= tick-common.o
-obj-$(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST)	+= tick-broadcast.o
+obj-$(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST)	+= tick-broadcast.o tick-broadcast-hrtimer.o
 obj-$(CONFIG_GENERIC_SCHED_CLOCK)		+= sched_clock.o
 obj-$(CONFIG_TICK_ONESHOT)			+= tick-oneshot.o
 obj-$(CONFIG_TICK_ONESHOT)			+= tick-sched.o
diff --git a/kernel/time/tick-broadcast-hrtimer.c b/kernel/time/tick-broadcast-hrtimer.c
new file mode 100644
index 0000000..23f4925
--- /dev/null
+++ b/kernel/time/tick-broadcast-hrtimer.c
@@ -0,0 +1,102 @@
+/*
+ * linux/kernel/time/tick-broadcast-hrtimer.c
+ * This file emulates a local clock event device
+ * via a pseudo clock device.
+ */
+#include <linux/cpu.h>
+#include <linux/err.h>
+#include <linux/hrtimer.h>
+#include <linux/interrupt.h>
+#include <linux/percpu.h>
+#include <linux/profile.h>
+#include <linux/clockchips.h>
+#include <linux/sched.h>
+#include <linux/smp.h>
+#include <linux/module.h>
+
+#include "tick-internal.h"
+
+static struct hrtimer bctimer;
+
+static void bc_set_mode(enum clock_event_mode mode,
+			struct clock_event_device *bc)
+{
+	switch (mode) {
+	case CLOCK_EVT_MODE_SHUTDOWN:
+		/*
+		 * Note, we cannot cancel the timer here as we might
+		 * run into the following live lock scenario:
+		 *
+		 * cpu 0		cpu1
+		 * lock(broadcast_lock);
+		 *			hrtimer_interrupt()
+		 *			bc_handler()
+		 *			   tick_handle_oneshot_broadcast();
+		 *			    lock(broadcast_lock);
+		 * hrtimer_cancel()
+		 *  wait_for_callback()
+		 */
+		hrtimer_try_to_cancel(&bctimer);
+		break;
+	default:
+		break;
+	}
+}
+
+/*
+ * This is called from the guts of the broadcast code when the cpu
+ * which is about to enter idle has the earliest broadcast timer event.
+ */
+static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
+{
+	ktime_t now, interval;
+	/*
+	 * We try to cancel the timer first. If the callback is on
+	 * flight on some other cpu then we let it handle it. If we
+	 * were able to cancel the timer nothing can rearm it as we
+	 * own broadcast_lock.
+	 *
+	 * However if we are called from the hrtimer interrupt handler
+	 * itself, reprogram it.
+	 */
+	if (hrtimer_try_to_cancel(&bctimer) >= 0) {
+		hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED);
+		/* Bind the "device" to the cpu */
+		bc->bound_on = smp_processor_id();
+	} else if (bc->bound_on == smp_processor_id()) {
+		now = ktime_get();
+		interval = ktime_sub(expires, now);
+		hrtimer_forward_now(&bctimer, interval);
+	}
+	return 0;
+}
+
+static struct clock_event_device ce_broadcast_hrtimer = {
+	.set_mode		= bc_set_mode,
+	.set_next_ktime		= bc_set_next,
+	.features		= CLOCK_EVT_FEAT_ONESHOT |
+				  CLOCK_EVT_FEAT_KTIME |
+				  CLOCK_EVT_FEAT_HRTIMER,
+	.rating			= 0,
+	.bound_on		= -1,
+	.min_delta_ns		= 1,
+	.max_delta_ns		= KTIME_MAX,
+	.min_delta_ticks	= 1,
+	.max_delta_ticks	= KTIME_MAX,
+	.mult			= 1,
+	.shift			= 0,
+	.cpumask		= cpu_all_mask,
+};
+
+static enum hrtimer_restart bc_handler(struct hrtimer *t)
+{
+	ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
+	return HRTIMER_RESTART;
+}
+
+void tick_setup_hrtimer_broadcast(void)
+{
+	hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+	bctimer.function = bc_handler;
+	clockevents_register_device(&ce_broadcast_hrtimer);
+}
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index be00692..7ed7e69 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -630,6 +630,42 @@ again:
 	raw_spin_unlock(&tick_broadcast_lock);
 }
 
+static int broadcast_needs_cpu(struct clock_event_device *bc, int cpu)
+{
+	if (!(bc->features & CLOCK_EVT_FEAT_HRTIMER))
+		return 0;
+	if (bc->next_event.tv64 == KTIME_MAX)
+		return 0;
+	return bc->bound_on == cpu ? -EBUSY : 0;
+}
+
+static void broadcast_shutdown_local(struct clock_event_device *bc,
+				     struct clock_event_device *dev)
+{
+	/*
+	 * For hrtimer based broadcasting we cannot shutdown the cpu
+	 * local device if our own event is the first one to expire or
+	 * if we own the broadcast timer.
+	 */
+	if (bc->features & CLOCK_EVT_FEAT_HRTIMER) {
+		if (broadcast_needs_cpu(bc, smp_processor_id()))
+			return;
+		if (dev->next_event.tv64 < bc->next_event.tv64)
+			return;
+	}
+	clockevents_set_mode(dev, CLOCK_EVT_MODE_SHUTDOWN);
+}
+
+static void broadcast_move_bc(int deadcpu)
+{
+	struct clock_event_device *bc = tick_broadcast_device.evtdev;
+
+	if (!bc || !broadcast_needs_cpu(bc, deadcpu))
+		return;
+	/* This moves the broadcast assignment to this cpu */
+	clockevents_program_event(bc, bc->next_event, 1);
+}
+
 /*
  * Powerstate information: The system enters/leaves a state, where
  * affected devices might stop
@@ -667,7 +703,7 @@ int tick_broadcast_oneshot_control(unsigned long reason)
 	if (reason == CLOCK_EVT_NOTIFY_BROADCAST_ENTER) {
 		if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_oneshot_mask)) {
 			WARN_ON_ONCE(cpumask_test_cpu(cpu, tick_broadcast_pending_mask));
-			clockevents_set_mode(dev, CLOCK_EVT_MODE_SHUTDOWN);
+			broadcast_shutdown_local(bc, dev);
 			/*
 			 * We only reprogram the broadcast timer if we
 			 * did not mark ourself in the force mask and
@@ -680,6 +716,11 @@ int tick_broadcast_oneshot_control(unsigned long reason)
 			    dev->next_event.tv64 < bc->next_event.tv64)
 				tick_broadcast_set_event(bc, cpu, dev->next_event, 1);
 		}
+		/*
+		 * If the current CPU owns the hrtimer broadcast
+		 * mechanism, it cannot go deep idle.
+		 */
+		ret = broadcast_needs_cpu(bc, cpu);
 	} else {
 		if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_oneshot_mask)) {
 			clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
@@ -853,6 +894,8 @@ void tick_shutdown_broadcast_oneshot(unsigned int *cpup)
 	cpumask_clear_cpu(cpu, tick_broadcast_pending_mask);
 	cpumask_clear_cpu(cpu, tick_broadcast_force_mask);
 
+	broadcast_move_bc(cpu);
+
 	raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
 }
 

Re: [PATCH V2 2/2] tick/cpuidle: Initialize hrtimer mode of broadcast

[Thomas Gleixner]

> +++ b/kernel/time/tick-broadcast-hrtimer.c
> +/*
> + * This is called from the guts of the broadcast code when the cpu
> + * which is about to enter idle has the earliest broadcast timer event.
> + */
> +static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
> +{
> +	ktime_t now, interval;
> +	/*
> +	 * We try to cancel the timer first. If the callback is on
> +	 * flight on some other cpu then we let it handle it. If we
> +	 * were able to cancel the timer nothing can rearm it as we
> +	 * own broadcast_lock.
> +	 *
> +	 * However if we are called from the hrtimer interrupt handler
> +	 * itself, reprogram it.
> +	 */
> +	if (hrtimer_try_to_cancel(&bctimer) >= 0) {
> +		hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED);
> +		/* Bind the "device" to the cpu */
> +		bc->bound_on = smp_processor_id();
> +	} else if (bc->bound_on == smp_processor_id()) {

This part really wants a proper comment. It took me a while to figure
out why this is correct and what the call chain is.


> +		now = ktime_get();
> +		interval = ktime_sub(expires, now);
> +		hrtimer_forward_now(&bctimer, interval);

We are in the event handler called from bc_handler() and expires is
absolute time. So what's wrong with calling
hrtimer_set_expires(&bctimer, expires)?

> +static enum hrtimer_restart bc_handler(struct hrtimer *t)
> +{
> +	ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
> +	return HRTIMER_RESTART;

We probably want to check whether the timer needs to be restarted at
all.

	if (ce_broadcast_timer.next_event.tv64 == KTIME_MAX)
	   return HRTIMER_NORESTART;

	return HRTIMER_RESTART;

Hmm?

Thanks,

	tglx

Re: [PATCH V2 2/2] tick/cpuidle: Initialize hrtimer mode of broadcast

[Preeti U Murthy]

Hi Thomas,

On 02/04/2014 03:48 PM, Thomas Gleixner wrote:
>> +++ b/kernel/time/tick-broadcast-hrtimer.c
>> +/*
>> + * This is called from the guts of the broadcast code when the cpu
>> + * which is about to enter idle has the earliest broadcast timer event.
>> + */
>> +static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
>> +{
>> +	ktime_t now, interval;
>> +	/*
>> +	 * We try to cancel the timer first. If the callback is on
>> +	 * flight on some other cpu then we let it handle it. If we
>> +	 * were able to cancel the timer nothing can rearm it as we
>> +	 * own broadcast_lock.
>> +	 *
>> +	 * However if we are called from the hrtimer interrupt handler
>> +	 * itself, reprogram it.
>> +	 */
>> +	if (hrtimer_try_to_cancel(&bctimer) >= 0) {
>> +		hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED);
>> +		/* Bind the "device" to the cpu */
>> +		bc->bound_on = smp_processor_id();
>> +	} else if (bc->bound_on == smp_processor_id()) {
> 
> This part really wants a proper comment. It took me a while to figure
> out why this is correct and what the call chain is.

How about:

"However we can also be called from the event handler of
ce_broadcast_hrtimer when bctimer expires. We cannot therefore restart
the timer since it is on flight on the same CPU. But due to the same
reason we can reset it."
?

> 
> 
>> +		now = ktime_get();
>> +		interval = ktime_sub(expires, now);
>> +		hrtimer_forward_now(&bctimer, interval);
> 
> We are in the event handler called from bc_handler() and expires is
> absolute time. So what's wrong with calling
> hrtimer_set_expires(&bctimer, expires)?

You are right. There are so many interfaces doing nearly the same thing
:( I overlooked that hrtimer_forward() and its variants were being used
when the interval was pre-calculated and stored away. And
hrtimer_set_expires() would be used when we knew the absolute expiry.
And it looks safe to call it here too.

> 
>> +static enum hrtimer_restart bc_handler(struct hrtimer *t)
>> +{
>> +	ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
>> +	return HRTIMER_RESTART;
> 
> We probably want to check whether the timer needs to be restarted at
> all.
> 
> 	if (ce_broadcast_timer.next_event.tv64 == KTIME_MAX)
> 	   return HRTIMER_NORESTART;
> 
> 	return HRTIMER_RESTART;

True this additional check would be useful.

Do you want me to send out the next version with the above corrections
including the patch added to this thread where we handle archs setting
the CPUIDLE_FLAG_TIMER_STOP flag?

> 
> Hmm?
> 
> Thanks,
> 
> 	tglx

Thanks

Regards
Preeti U Murthy
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev
> 

Re: [PATCH V2 2/2] tick/cpuidle: Initialize hrtimer mode of broadcast

[Thomas Gleixner]

On Tue, 4 Feb 2014, Preeti U Murthy wrote:
> Do you want me to send out the next version with the above corrections
> including the patch added to this thread where we handle archs setting
> the CPUIDLE_FLAG_TIMER_STOP flag?

Yes please.

Re: [PATCH V2 0/2] time/cpuidle: Support in tick broadcast framework in absence of external clock device

[Preeti U Murthy]

Hi Thomas,

I realized that the below patch is also required for this patchset.

This patch apart, I noticed that there is also one corner case which we will
need to handle. The BROADCAST_ON notifications in periodic mode
(oneshot mode is a nop).
  We will need to fail the BROADCAST_ON notification too in this case if the
CPU in question is made the stand by CPU. 

Thanks

Regards
Preeti U Murthy

---------------------------------------------------------------------------------

time/cpuidle:Handle failed call to BROADCAST_ENTER on archs with CPUIDLE_FLAG_TIMER_STOP set

From: Preeti U Murthy <preeti@linux.vnet.ibm.com>

Some archs set the CPUIDLE_FLAG_TIMER_STOP flag for idle states in which the
local timers stop. The cpuidle_idle_call() currently handles such idle states
by calling into the broadcast framework so as to wakeup CPUs at their next
wakeup event. With the hrtimer mode of broadcast, the BROADCAST_ENTER call
into the broadcast frameowork can fail for archs that do not have an external
clock device to handle wakeups and the CPU in question has to thus be made
the stand by CPU. This patch handles such cases by failing the call into
cpuidle so that the arch can take some default action. The arch will certainly
not enter a similar idle state because a failed cpuidle call will also implicitly
indicate that the broadcast framework has not registered this CPU to be woken up.
Hence we are safe if we fail the cpuidle call.

In the process move the functions that trace idle statistics just before and
after the entry and exit into idle states respectively. In other
scenarios where the call to cpuidle fails, we end up not tracing idle
entry and exit since a decision on an idle state could not be taken. Similarly
when the call to broadcast framework fails, we skip tracing idle statistics
because we are in no further position to take a decision on an alternative
idle state to enter into.

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
---
 drivers/cpuidle/cpuidle.c |   38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index a55e68f..8f42033 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -117,15 +117,19 @@ int cpuidle_idle_call(void)
 {
 	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
 	struct cpuidle_driver *drv;
-	int next_state, entered_state;
-	bool broadcast;
+	int next_state, entered_state, ret = 0;
+	bool broadcast = false;
 
-	if (off || !initialized)
-		return -ENODEV;
+	if (off || !initialized) {
+		ret = -ENODEV;
+		goto out;
+	}
 
 	/* check if the device is ready */
-	if (!dev || !dev->enabled)
-		return -EBUSY;
+	if (!dev || !dev->enabled) {
+		ret = -EBUSY;
+		goto out;
+	}
 
 	drv = cpuidle_get_cpu_driver(dev);
 
@@ -137,15 +141,18 @@ int cpuidle_idle_call(void)
 		if (cpuidle_curr_governor->reflect)
 			cpuidle_curr_governor->reflect(dev, next_state);
 		local_irq_enable();
-		return 0;
+		goto out;
 	}
 
-	trace_cpu_idle_rcuidle(next_state, dev->cpu);
-
 	broadcast = !!(drv->states[next_state].flags & CPUIDLE_FLAG_TIMER_STOP);
 
-	if (broadcast)
-		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu);
+	if (broadcast) {
+		ret = clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu);
+		if (ret)
+			goto out;
+	}
+
+	trace_cpu_idle_rcuidle(next_state, dev->cpu);
 
 	if (cpuidle_state_is_coupled(dev, drv, next_state))
 		entered_state = cpuidle_enter_state_coupled(dev, drv,
@@ -153,16 +160,17 @@ int cpuidle_idle_call(void)
 	else
 		entered_state = cpuidle_enter_state(dev, drv, next_state);
 
-	if (broadcast)
-		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
-
 	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
 
 	/* give the governor an opportunity to reflect on the outcome */
 	if (cpuidle_curr_governor->reflect)
 		cpuidle_curr_governor->reflect(dev, entered_state);
 
-	return 0;
+out:	if (broadcast)
+		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
+
+
+	return ret;
 }
 
 /**