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Subject[patch 35/46] tick-management: broadcast functionality
From: Thomas Gleixner <tglx@linutronix.de>
From: Ingo Molnar <mingo@elte.hu>

Add broadcast functionality, so per cpu clock event devices can be
registered as dummy devices or switched from/to broadcast on demand.
The broadcast function distributes the events via the broadcast
function of the clock event device. This is primarily designed to
replace the switch apic timer to / from IPI in power states, where the
apic stops.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
kernel/time/Makefile | 5
kernel/time/tick-broadcast.c | 258 +++++++++++++++++++++++++++++++++++++++++++
kernel/time/tick-common.c | 63 +++++++---
kernel/time/tick-internal.h | 74 ++++++++++++
4 files changed, 378 insertions(+), 22 deletions(-)
Index: linux-2.6.20-rc4-mm1-bo/kernel/time/Makefile
===================================================================
--- linux-2.6.20-rc4-mm1-bo.orig/kernel/time/Makefile
+++ linux-2.6.20-rc4-mm1-bo/kernel/time/Makefile
@@ -1,4 +1,5 @@
obj-y += ntp.o clocksource.o jiffies.o

-obj-$(CONFIG_GENERIC_CLOCKEVENTS) += clockevents.o
-obj-$(CONFIG_GENERIC_CLOCKEVENTS) += tick-common.o
+obj-$(CONFIG_GENERIC_CLOCKEVENTS) += clockevents.o
+obj-$(CONFIG_GENERIC_CLOCKEVENTS) += tick-common.o
+obj-$(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) += tick-broadcast.o
Index: linux-2.6.20-rc4-mm1-bo/kernel/time/tick-broadcast.c
===================================================================
--- /dev/null
+++ linux-2.6.20-rc4-mm1-bo/kernel/time/tick-broadcast.c
@@ -0,0 +1,258 @@
+/*
+ * linux/kernel/time/tick-broadcast.c
+ *
+ * This file contains functions which emulate a local clock-event
+ * device via a broadcast event source.
+ *
+ * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
+ * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
+ * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
+ *
+ * This code is licenced under the GPL version 2. For details see
+ * kernel-base/COPYING.
+ */
+#include <linux/cpu.h>
+#include <linux/err.h>
+#include <linux/hrtimer.h>
+#include <linux/irq.h>
+#include <linux/percpu.h>
+#include <linux/profile.h>
+#include <linux/sched.h>
+#include <linux/tick.h>
+
+#include "tick-internal.h"
+
+/*
+ * Broadcast support for broken x86 hardware, where the local apic
+ * timer stops in C3 state.
+ */
+
+struct tick_device tick_broadcast_device;
+static cpumask_t tick_broadcast_mask;
+DEFINE_SPINLOCK(tick_broadcast_lock);
+
+/*
+ * Start the device in periodic mode
+ */
+static void tick_broadcast_start_periodic(struct clock_event_device *bc)
+{
+ if (bc && bc->mode == CLOCK_EVT_MODE_SHUTDOWN)
+ tick_setup_periodic(bc, 1);
+}
+
+/*
+ * Check, if the device can be utilized as broadcast device:
+ */
+int tick_check_broadcast_device(struct clock_event_device *dev)
+{
+ if (tick_broadcast_device.evtdev ||
+ (dev->features & CLOCK_EVT_FEAT_C3STOP))
+ return 0;
+
+ clockevents_exchange_device(NULL, dev);
+ tick_broadcast_device.evtdev = dev;
+ if (!cpus_empty(tick_broadcast_mask))
+ tick_broadcast_start_periodic(dev);
+ return 1;
+}
+
+/*
+ * Check, if the device is the broadcast device
+ */
+int tick_is_broadcast_device(struct clock_event_device *dev)
+{
+ return (dev && tick_broadcast_device.evtdev == dev);
+}
+
+/*
+ * Check, if the device is disfunctional and a place holder, which
+ * needs to be handled by the broadcast device.
+ */
+int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu)
+{
+ unsigned long flags;
+ int ret = 0;
+
+ spin_lock_irqsave(&tick_broadcast_lock, flags);
+
+ /*
+ * Devices might be registered with both periodic and oneshot
+ * mode disabled. This signals, that the device needs to be
+ * operated from the broadcast device and is a placeholder for
+ * the cpu local device.
+ */
+ if (!tick_device_is_functional(dev)) {
+ dev->event_handler = tick_handle_periodic;
+ cpu_set(cpu, tick_broadcast_mask);
+ tick_broadcast_start_periodic(tick_broadcast_device.evtdev);
+ ret = 1;
+ }
+
+ spin_unlock_irqrestore(&tick_broadcast_lock, flags);
+ return ret;
+}
+
+/*
+ * Broadcast the event to the cpus, which are set in the mask
+ */
+int tick_do_broadcast(cpumask_t mask)
+{
+ int ret = 0, cpu = smp_processor_id();
+ struct tick_device *td;
+
+ /*
+ * Check, if the current cpu is in the mask
+ */
+ if (cpu_isset(cpu, mask)) {
+ cpu_clear(cpu, mask);
+ td = &per_cpu(tick_cpu_device, cpu);
+ td->evtdev->event_handler(td->evtdev);
+ ret = 1;
+ }
+
+ if (!cpus_empty(mask)) {
+ /*
+ * It might be necessary to actually check whether the devices
+ * have different broadcast functions. For now, just use the
+ * one of the first device. This works as long as we have this
+ * misfeature only on x86 (lapic)
+ */
+ cpu = first_cpu(mask);
+ td = &per_cpu(tick_cpu_device, cpu);
+ td->evtdev->broadcast(mask);
+ ret = 1;
+ }
+ return ret;
+}
+
+/*
+ * Periodic broadcast:
+ * - invoke the broadcast handlers
+ */
+static void tick_do_periodic_broadcast(void)
+{
+ cpumask_t mask;
+
+ spin_lock(&tick_broadcast_lock);
+
+ cpus_and(mask, cpu_online_map, tick_broadcast_mask);
+ tick_do_broadcast(mask);
+
+ spin_unlock(&tick_broadcast_lock);
+}
+
+/*
+ * Event handler for periodic broadcast ticks
+ */
+static void tick_handle_periodic_broadcast(struct clock_event_device *dev)
+{
+ tick_do_periodic_broadcast();
+
+ /*
+ * The device is in periodic mode. No reprogramming necessary:
+ */
+ if (dev->mode == CLOCK_EVT_MODE_PERIODIC)
+ return;
+
+ /*
+ * Setup the next period for devices, which do not have
+ * periodic mode:
+ */
+ for (;;) {
+ ktime_t next = ktime_add(dev->next_event, tick_period);
+
+ if (!clockevents_program_event(dev, next))
+ return;
+ tick_do_periodic_broadcast();
+ }
+}
+
+/*
+ * Powerstate information: The system enters/leaves a state, where
+ * affected devices might stop
+ */
+static void tick_do_broadcast_on_off(void *why)
+{
+ struct clock_event_device *bc, *dev;
+ struct tick_device *td;
+ unsigned long flags, *reason = why;
+ int cpu;
+
+ spin_lock_irqsave(&tick_broadcast_lock, flags);
+
+ cpu = smp_processor_id();
+ td = &per_cpu(tick_cpu_device, cpu);
+ dev = td->evtdev;
+ bc = tick_broadcast_device.evtdev;
+
+ /*
+ * Is the device in broadcast mode forever or is it not
+ * affected by the powerstate ?
+ */
+ if (!dev || !tick_device_is_functional(dev) ||
+ !(dev->features & CLOCK_EVT_FEAT_C3STOP))
+ goto out;
+
+ if (*reason == CLOCK_EVT_NOTIFY_BROADCAST_ON) {
+ if (!cpu_isset(cpu, tick_broadcast_mask)) {
+ cpu_set(cpu, tick_broadcast_mask);
+ if (td->mode == TICKDEV_MODE_PERIODIC)
+ clockevents_set_mode(dev,
+ CLOCK_EVT_MODE_SHUTDOWN);
+ }
+ } else {
+ if (cpu_isset(cpu, tick_broadcast_mask)) {
+ cpu_clear(cpu, tick_broadcast_mask);
+ if (td->mode == TICKDEV_MODE_PERIODIC)
+ tick_setup_periodic(dev, 0);
+ }
+ }
+
+ if (cpus_empty(tick_broadcast_mask))
+ clockevents_set_mode(bc, CLOCK_EVT_MODE_SHUTDOWN);
+ else {
+ if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
+ tick_broadcast_start_periodic(bc);
+ }
+out:
+ spin_unlock_irqrestore(&tick_broadcast_lock, flags);
+}
+
+/*
+ * Powerstate information: The system enters/leaves a state, where
+ * affected devices might stop.
+ */
+void tick_broadcast_on_off(unsigned long reason, int *oncpu)
+{
+ int cpu = get_cpu();
+
+ if (cpu == *oncpu)
+ tick_do_broadcast_on_off(&reason);
+ else
+ smp_call_function_single(*oncpu, tick_do_broadcast_on_off,
+ &reason, 1, 1);
+ put_cpu();
+}
+
+/*
+ * Set the periodic handler depending on broadcast on/off
+ */
+void tick_set_periodic_handler(struct clock_event_device *dev, int broadcast)
+{
+ if (!broadcast)
+ dev->event_handler = tick_handle_periodic;
+ else
+ dev->event_handler = tick_handle_periodic_broadcast;
+}
+
+/*
+ * Called with irqs disabled
+ */
+void tick_do_resume(int cpu)
+{
+ unsigned long reason;
+
+ reason = cpu_isset(cpu, tick_broadcast_mask) ?
+ CLOCK_EVT_NOTIFY_BROADCAST_ON : CLOCK_EVT_NOTIFY_BROADCAST_OFF;
+ tick_do_broadcast_on_off(&reason);
+}
Index: linux-2.6.20-rc4-mm1-bo/kernel/time/tick-common.c
===================================================================
--- linux-2.6.20-rc4-mm1-bo.orig/kernel/time/tick-common.c
+++ linux-2.6.20-rc4-mm1-bo/kernel/time/tick-common.c
@@ -20,17 +20,19 @@
#include <linux/sched.h>
#include <linux/tick.h>

+#include "tick-internal.h"
+
/*
* Tick devices
*/
-static DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
+DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
/*
* Tick next event: keeps track of the tick time
*/
-static ktime_t tick_next_period;
-static ktime_t tick_period;
+ktime_t tick_next_period;
+ktime_t tick_period;
static int tick_do_timer_cpu = -1;
-static DEFINE_SPINLOCK(tick_device_lock);
+DEFINE_SPINLOCK(tick_device_lock);

/*
* Periodic tick
@@ -78,9 +80,13 @@ void tick_handle_periodic(struct clock_e
/*
* Setup the device for a periodic tick
*/
-void tick_setup_periodic(struct clock_event_device *dev)
+void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
{
- dev->event_handler = tick_handle_periodic;
+ tick_set_periodic_handler(dev, broadcast);
+
+ /* Broadcast setup ? */
+ if (!tick_device_is_functional(dev))
+ return;

if (dev->features & CLOCK_EVT_FEAT_PERIODIC) {
clockevents_set_mode(dev, CLOCK_EVT_MODE_PERIODIC);
@@ -145,6 +151,15 @@ static void tick_setup_device(struct tic
if (!cpus_equal(newdev->cpumask, cpumask))
irq_set_affinity(newdev->irq, cpumask);

+ /*
+ * When global broadcasting is active, check if the current
+ * device is registered as a placeholder for broadcast mode.
+ * This allows us to handle this x86 misfeature in a generic
+ * way.
+ */
+ if (tick_device_uses_broadcast(newdev, cpu))
+ return;
+
if (td->mode == TICKDEV_MODE_PERIODIC)
tick_setup_periodic(newdev, 0);
}
@@ -197,31 +212,34 @@ static int tick_check_new_device(struct
* Check the rating
*/
if (curdev->rating >= newdev->rating)
- goto out;
+ goto out_bc;
}

/*
* Replace the eventually existing device by the new
- * device.
+ * device. If the current device is the broadcast device, do
+ * not give it back to the clockevents layer !
*/
+ if (tick_is_broadcast_device(curdev)) {
+ clockevents_set_mode(curdev, CLOCK_EVT_MODE_SHUTDOWN);
+ curdev = NULL;
+ }
clockevents_exchange_device(curdev, newdev);
tick_setup_device(td, newdev, cpu, cpumask);
- ret = NOTIFY_STOP;

-out:
spin_unlock_irqrestore(&tick_device_lock, flags);
- return ret;
-}
+ return NOTIFY_STOP;

-/*
- * Called with irqs disabled
- */
-static inline void tick_do_resume(int cpu)
-{
- struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
+out_bc:
+ /*
+ * Can the new device be used as a broadcast device ?
+ */
+ if (tick_check_broadcast_device(newdev))
+ ret = NOTIFY_STOP;
+out:
+ spin_unlock_irqrestore(&tick_device_lock, flags);

- if (td->mode == TICKDEV_MODE_PERIODIC)
- tick_setup_periodic(td->evtdev, 0);
+ return ret;
}

/*
@@ -247,6 +265,11 @@ static int tick_notify(struct notifier_b
case CLOCK_EVT_NOTIFY_ADD:
return tick_check_new_device(dev);

+ case CLOCK_EVT_NOTIFY_BROADCAST_ON:
+ case CLOCK_EVT_NOTIFY_BROADCAST_OFF:
+ tick_broadcast_on_off(reason, dev);
+ break;
+
case CLOCK_EVT_NOTIFY_RESUME:
tick_resume();
break;
Index: linux-2.6.20-rc4-mm1-bo/kernel/time/tick-internal.h
===================================================================
--- /dev/null
+++ linux-2.6.20-rc4-mm1-bo/kernel/time/tick-internal.h
@@ -0,0 +1,74 @@
+/*
+ * tick internal variable and functions used by low/high res code
+ */
+DECLARE_PER_CPU(struct tick_device, tick_cpu_device);
+extern spinlock_t tick_device_lock;
+extern ktime_t tick_next_period;
+extern ktime_t tick_period;
+
+extern void tick_setup_periodic(struct clock_event_device *dev, int broadcast);
+extern void tick_handle_periodic(struct clock_event_device *dev);
+
+/*
+ * Broadcasting support
+ */
+#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
+extern int tick_do_broadcast(cpumask_t mask);
+extern struct tick_device tick_broadcast_device;
+extern spinlock_t tick_broadcast_lock;
+
+extern int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu);
+extern int tick_check_broadcast_device(struct clock_event_device *dev);
+extern int tick_is_broadcast_device(struct clock_event_device *dev);
+extern void tick_broadcast_on_off(unsigned long reason, int *oncpu);
+
+extern void
+tick_set_periodic_handler(struct clock_event_device *dev, int broadcast);
+extern void tick_do_resume(int cpu);
+
+#else /* !BROADCAST */
+
+static inline int tick_check_broadcast_device(struct clock_event_device *dev)
+{
+ return 0;
+}
+
+static inline int tick_is_broadcast_device(struct clock_event_device *dev)
+{
+ return 0;
+}
+static inline int tick_device_uses_broadcast(struct clock_event_device *dev,
+ int cpu)
+{
+ return 0;
+}
+static inline void tick_do_periodic_broadcast(struct clock_event_device *d) { }
+static inline void tick_broadcast_on_off(unsigned long reason, int *oncpu) { }
+
+/*
+ * Set the periodic handler in non broadcast mode
+ */
+static inline void tick_set_periodic_handler(struct clock_event_device *dev,
+ int broadcast)
+{
+ dev->event_handler = tick_handle_periodic;
+}
+/*
+ * Called with irqs disabled
+ */
+static inline void tick_do_resume(int cpu)
+{
+ struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
+
+ if (td->mode == TICKDEV_MODE_PERIODIC)
+ tick_setup_periodic(td->evtdev, 0);
+}
+#endif /* !BROADCAST */
+
+/*
+ * Check, if the device is functional or a dummy for broadcast
+ */
+static inline int tick_device_is_functional(struct clock_event_device *dev)
+{
+ return !(dev->features & CLOCK_EVT_FEAT_DUMMY);
+}
--

-
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