[PATCH] tick-management: core functionality

With Ingo Molnar <mingo@elte.hu>

The tick-management code is the first user of the clockevents layer.  It takes
clock event devices from the clock events core and uses them to provide the
periodic tick.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 279 insertions, 1 deletions

diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index 2bf1805914d0..337daef72755 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -1,3 +1,4 @@
 obj-y += ntp.o clocksource.o jiffies.o
 
-obj-$(CONFIG_GENERIC_CLOCKEVENTS) += clockevents.o
+obj-$(CONFIG_GENERIC_CLOCKEVENTS)       += clockevents.o
+obj-$(CONFIG_GENERIC_CLOCKEVENTS)       += tick-common.o
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
new file mode 100644
index 000000000000..46e4381c26ea
--- /dev/null
+++ b/kernel/time/tick-common.c
@@ -0,0 +1,277 @@
+/*
+ * linux/kernel/time/tick-common.c
+ *
+ * This file contains the base functions to manage periodic tick
+ * related events.
+ *
+ * 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>
+
+/*
+ * Tick devices
+ */
+static 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;
+static int tick_do_timer_cpu = -1;
+static DEFINE_SPINLOCK(tick_device_lock);
+
+/*
+ * Periodic tick
+ */
+static void tick_periodic(int cpu)
+{
+        if (tick_do_timer_cpu == cpu) {
+                write_seqlock(&xtime_lock);
+
+                /* Keep track of the next tick event */
+                tick_next_period = ktime_add(tick_next_period, tick_period);
+
+                do_timer(1);
+                write_sequnlock(&xtime_lock);
+        }
+
+        update_process_times(user_mode(get_irq_regs()));
+        profile_tick(CPU_PROFILING);
+}
+
+/*
+ * Event handler for periodic ticks
+ */
+void tick_handle_periodic(struct clock_event_device *dev)
+{
+        int cpu = smp_processor_id();
+
+        tick_periodic(cpu);
+
+        if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
+                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, ktime_get()))
+                        return;
+                tick_periodic(cpu);
+        }
+}
+
+/*
+ * Setup the device for a periodic tick
+ */
+void tick_setup_periodic(struct clock_event_device *dev)
+{
+        dev->event_handler = tick_handle_periodic;
+
+        if (dev->features & CLOCK_EVT_FEAT_PERIODIC) {
+                clockevents_set_mode(dev, CLOCK_EVT_MODE_PERIODIC);
+        } else {
+                unsigned long seq;
+                ktime_t next;
+
+                do {
+                        seq = read_seqbegin(&xtime_lock);
+                        next = tick_next_period;
+                } while (read_seqretry(&xtime_lock, seq));
+
+                clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
+
+                for (;;) {
+                        if (!clockevents_program_event(dev, next, ktime_get()))
+                                return;
+                        next = ktime_add(next, tick_period);
+                }
+        }
+}
+
+/*
+ * Setup the tick device
+ */
+static void tick_setup_device(struct tick_device *td,
+                              struct clock_event_device *newdev, int cpu,
+                              cpumask_t cpumask)
+{
+        ktime_t next_event;
+        void (*handler)(struct clock_event_device *) = NULL;
+
+        /*
+         * First device setup ?
+         */
+        if (!td->evtdev) {
+                /*
+                 * If no cpu took the do_timer update, assign it to
+                 * this cpu:
+                 */
+                if (tick_do_timer_cpu == -1) {
+                        tick_do_timer_cpu = cpu;
+                        tick_next_period = ktime_get();
+                        tick_period = ktime_set(0, NSEC_PER_SEC / HZ);
+                }
+
+                /*
+                 * Startup in periodic mode first.
+                 */
+                td->mode = TICKDEV_MODE_PERIODIC;
+        } else {
+                handler = td->evtdev->event_handler;
+                next_event = td->evtdev->next_event;
+        }
+
+        td->evtdev = newdev;
+
+        /*
+         * When the device is not per cpu, pin the interrupt to the
+         * current cpu:
+         */
+        if (!cpus_equal(newdev->cpumask, cpumask))
+                irq_set_affinity(newdev->irq, cpumask);
+
+        if (td->mode == TICKDEV_MODE_PERIODIC)
+                tick_setup_periodic(newdev, 0);
+}
+
+/*
+ * Check, if the new registered device should be used.
+ */
+static int tick_check_new_device(struct clock_event_device *newdev)
+{
+        struct clock_event_device *curdev;
+        struct tick_device *td;
+        int cpu, ret = NOTIFY_OK;
+        unsigned long flags;
+        cpumask_t cpumask;
+
+        spin_lock_irqsave(&tick_device_lock, flags);
+
+        cpu = smp_processor_id();
+        if (!cpu_isset(cpu, newdev->cpumask))
+                goto out;
+
+        td = &per_cpu(tick_cpu_device, cpu);
+        curdev = td->evtdev;
+        cpumask = cpumask_of_cpu(cpu);
+
+        /* cpu local device ? */
+        if (!cpus_equal(newdev->cpumask, cpumask)) {
+
+                /*
+                 * If the cpu affinity of the device interrupt can not
+                 * be set, ignore it.
+                 */
+                if (!irq_can_set_affinity(newdev->irq))
+                        goto out_bc;
+
+                /*
+                 * If we have a cpu local device already, do not replace it
+                 * by a non cpu local device
+                 */
+                if (curdev && cpus_equal(curdev->cpumask, cpumask))
+                        goto out_bc;
+        }
+
+        /*
+         * If we have an active device, then check the rating and the oneshot
+         * feature.
+         */
+        if (curdev) {
+                /*
+                 * Check the rating
+                 */
+                if (curdev->rating >= newdev->rating)
+                        goto out;
+        }
+
+        /*
+         * Replace the eventually existing device by the new
+         * device.
+         */
+        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;
+}
+
+/*
+ * Shutdown an event device on a given cpu:
+ *
+ * This is called on a life CPU, when a CPU is dead. So we cannot
+ * access the hardware device itself.
+ * We just set the mode and remove it from the lists.
+ */
+static void tick_shutdown(unsigned int *cpup)
+{
+        struct tick_device *td = &per_cpu(tick_cpu_device, *cpup);
+        struct clock_event_device *dev = td->evtdev;
+        unsigned long flags;
+
+        spin_lock_irqsave(&tick_device_lock, flags);
+        td->mode = TICKDEV_MODE_PERIODIC;
+        if (dev) {
+                /*
+                 * Prevent that the clock events layer tries to call
+                 * the set mode function!
+                 */
+                dev->mode = CLOCK_EVT_MODE_UNUSED;
+                clockevents_exchange_device(dev, NULL);
+                td->evtdev = NULL;
+        }
+        spin_unlock_irqrestore(&tick_device_lock, flags);
+}
+
+/*
+ * Notification about clock event devices
+ */
+static int tick_notify(struct notifier_block *nb, unsigned long reason,
+                               void *dev)
+{
+        switch (reason) {
+
+        case CLOCK_EVT_NOTIFY_ADD:
+                return tick_check_new_device(dev);
+
+        case CLOCK_EVT_NOTIFY_CPU_DEAD:
+                tick_shutdown(dev);
+                break;
+
+        default:
+                break;
+        }
+
+        return NOTIFY_OK;
+}
+
+static struct notifier_block tick_notifier = {
+        .notifier_call = tick_notify,
+};
+
+/**
+ * tick_init - initialize the tick control
+ *
+ * Register the notifier with the clockevents framework
+ */
+void __init tick_init(void)
+{
+        clockevents_register_notifier(&tick_notifier);
+}