[PATCH] tick-management: dyntick / highres functionality

With Ingo Molnar <mingo@elte.hu>

Add functions to provide dynamic ticks and high resolution timers.  The code
which keeps track of jiffies and handles the long idle periods is shared
between tick based and high resolution timer based dynticks.  The dyntick
functionality can be disabled on the kernel commandline.  Provide also the
infrastructure to support high resolution timers.

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>

1 files changed, 84 insertions, 0 deletions

diff --git a/kernel/time/tick-oneshot.c b/kernel/time/tick-oneshot.c
new file mode 100644
index 000000000000..2e8b7ff863cc
--- /dev/null
+++ b/kernel/time/tick-oneshot.c
@@ -0,0 +1,84 @@
+/*
+ * linux/kernel/time/tick-oneshot.c
+ *
+ * This file contains functions which manage high resolution 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>
+
+#include "tick-internal.h"
+
+/**
+ * tick_program_event
+ */
+int tick_program_event(ktime_t expires, int force)
+{
+        struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
+        ktime_t now = ktime_get();
+
+        while (1) {
+                int ret = clockevents_program_event(dev, expires, now);
+
+                if (!ret || !force)
+                        return ret;
+                now = ktime_get();
+                expires = ktime_add(now, ktime_set(0, dev->min_delta_ns));
+        }
+}
+
+/**
+ * tick_setup_oneshot - setup the event device for oneshot mode (hres or nohz)
+ */
+void tick_setup_oneshot(struct clock_event_device *newdev,
+                        void (*handler)(struct clock_event_device *),
+                        ktime_t next_event)
+{
+        newdev->event_handler = handler;
+        clockevents_set_mode(newdev, CLOCK_EVT_MODE_ONESHOT);
+        clockevents_program_event(newdev, next_event, ktime_get());
+}
+
+/**
+ * tick_switch_to_oneshot - switch to oneshot mode
+ */
+int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *))
+{
+        struct tick_device *td = &__get_cpu_var(tick_cpu_device);
+        struct clock_event_device *dev = td->evtdev;
+
+        if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT) ||
+            !tick_device_is_functional(dev))
+                return -EINVAL;
+
+        td->mode = TICKDEV_MODE_ONESHOT;
+        dev->event_handler = handler;
+        clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
+        tick_broadcast_switch_to_oneshot();
+        return 0;
+}
+
+#ifdef CONFIG_HIGH_RES_TIMERS
+/**
+ * tick_init_highres - switch to high resolution mode
+ *
+ * Called with interrupts disabled.
+ */
+int tick_init_highres(void)
+{
+        return tick_switch_to_oneshot(hrtimer_interrupt);
+}
+#endif