sched: add optional support for CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

this replaces the rq->clock stuff (and possibly cpu_clock()).

 - architectures that have an 'imperfect' hardware clock can set
   CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

 - the 'jiffie' window might be superfulous when we update tick_gtod
   before the __update_sched_clock() call in sched_clock_tick()

 - cpu_clock() might be implemented as:

     sched_clock_cpu(smp_processor_id())

   if the accuracy proves good enough - how far can TSC drift in a
   single jiffie when considering the filtering and idle hooks?

[ mingo@elte.hu: various fixes and cleanups ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 236 insertions, 0 deletions

diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
new file mode 100644
index 00000000000..9c597e37f7d
--- /dev/null
+++ b/kernel/sched_clock.c
@@ -0,0 +1,236 @@
+/*
+ * sched_clock for unstable cpu clocks
+ *
+ *  Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
+ *
+ * Based on code by:
+ *   Ingo Molnar <mingo@redhat.com>
+ *   Guillaume Chazarain <guichaz@gmail.com>
+ *
+ * Create a semi stable clock from a mixture of other events, including:
+ *  - gtod
+ *  - jiffies
+ *  - sched_clock()
+ *  - explicit idle events
+ *
+ * We use gtod as base and the unstable clock deltas. The deltas are filtered,
+ * making it monotonic and keeping it within an expected window.  This window
+ * is set up using jiffies.
+ *
+ * Furthermore, explicit sleep and wakeup hooks allow us to account for time
+ * that is otherwise invisible (TSC gets stopped).
+ *
+ * The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
+ * consistent between cpus (never more than 1 jiffies difference).
+ */
+#include <linux/sched.h>
+#include <linux/percpu.h>
+#include <linux/spinlock.h>
+#include <linux/ktime.h>
+#include <linux/module.h>
+
+
+#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+
+struct sched_clock_data {
+	/*
+	 * Raw spinlock - this is a special case: this might be called
+	 * from within instrumentation code so we dont want to do any
+	 * instrumentation ourselves.
+	 */
+	raw_spinlock_t		lock;
+
+	unsigned long		prev_jiffies;
+	u64			prev_raw;
+	u64			tick_raw;
+	u64			tick_gtod;
+	u64			clock;
+};
+
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
+
+static inline struct sched_clock_data *this_scd(void)
+{
+	return &__get_cpu_var(sched_clock_data);
+}
+
+static inline struct sched_clock_data *cpu_sdc(int cpu)
+{
+	return &per_cpu(sched_clock_data, cpu);
+}
+
+void sched_clock_init(void)
+{
+	u64 ktime_now = ktime_to_ns(ktime_get());
+	u64 now = 0;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		struct sched_clock_data *scd = cpu_sdc(cpu);
+
+		scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
+		scd->prev_jiffies = jiffies;
+		scd->prev_raw = now;
+		scd->tick_raw = now;
+		scd->tick_gtod = ktime_now;
+		scd->clock = ktime_now;
+	}
+}
+
+/*
+ * update the percpu scd from the raw @now value
+ *
+ *  - filter out backward motion
+ *  - use jiffies to generate a min,max window to clip the raw values
+ */
+static void __update_sched_clock(struct sched_clock_data *scd, u64 now)
+{
+	unsigned long now_jiffies = jiffies;
+	long delta_jiffies = now_jiffies - scd->prev_jiffies;
+	u64 clock = scd->clock;
+	u64 min_clock, max_clock;
+	s64 delta = now - scd->prev_raw;
+
+	WARN_ON_ONCE(!irqs_disabled());
+	min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC;
+
+	if (unlikely(delta < 0)) {
+		clock++;
+		goto out;
+	}
+
+	max_clock = min_clock + TICK_NSEC;
+
+	if (unlikely(clock + delta > max_clock)) {
+		if (clock < max_clock)
+			clock = max_clock;
+		else
+			clock++;
+	} else {
+		clock += delta;
+	}
+
+ out:
+	if (unlikely(clock < min_clock))
+		clock = min_clock;
+
+	scd->prev_raw = now;
+	scd->prev_jiffies = now_jiffies;
+	scd->clock = clock;
+}
+
+static void lock_double_clock(struct sched_clock_data *data1,
+				struct sched_clock_data *data2)
+{
+	if (data1 < data2) {
+		__raw_spin_lock(&data1->lock);
+		__raw_spin_lock(&data2->lock);
+	} else {
+		__raw_spin_lock(&data2->lock);
+		__raw_spin_lock(&data1->lock);
+	}
+}
+
+u64 sched_clock_cpu(int cpu)
+{
+	struct sched_clock_data *scd = cpu_sdc(cpu);
+	u64 now, clock;
+
+	WARN_ON_ONCE(!irqs_disabled());
+	now = sched_clock();
+
+	if (cpu != raw_smp_processor_id()) {
+		/*
+		 * in order to update a remote cpu's clock based on our
+		 * unstable raw time rebase it against:
+		 *   tick_raw		(offset between raw counters)
+		 *   tick_gotd          (tick offset between cpus)
+		 */
+		struct sched_clock_data *my_scd = this_scd();
+
+		lock_double_clock(scd, my_scd);
+
+		now -= my_scd->tick_raw;
+		now += scd->tick_raw;
+
+		now -= my_scd->tick_gtod;
+		now += scd->tick_gtod;
+
+		__raw_spin_unlock(&my_scd->lock);
+	} else {
+		__raw_spin_lock(&scd->lock);
+	}
+
+	__update_sched_clock(scd, now);
+	clock = scd->clock;
+
+	__raw_spin_unlock(&scd->lock);
+
+	return clock;
+}
+
+void sched_clock_tick(void)
+{
+	struct sched_clock_data *scd = this_scd();
+	u64 now, now_gtod;
+
+	WARN_ON_ONCE(!irqs_disabled());
+
+	now = sched_clock();
+	now_gtod = ktime_to_ns(ktime_get());
+
+	__raw_spin_lock(&scd->lock);
+	__update_sched_clock(scd, now);
+	/*
+	 * update tick_gtod after __update_sched_clock() because that will
+	 * already observe 1 new jiffy; adding a new tick_gtod to that would
+	 * increase the clock 2 jiffies.
+	 */
+	scd->tick_raw = now;
+	scd->tick_gtod = now_gtod;
+	__raw_spin_unlock(&scd->lock);
+}
+
+/*
+ * We are going deep-idle (irqs are disabled):
+ */
+void sched_clock_idle_sleep_event(void)
+{
+	sched_clock_cpu(smp_processor_id());
+}
+EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
+
+/*
+ * We just idled delta nanoseconds (called with irqs disabled):
+ */
+void sched_clock_idle_wakeup_event(u64 delta_ns)
+{
+	struct sched_clock_data *scd = this_scd();
+	u64 now = sched_clock();
+
+	/*
+	 * Override the previous timestamp and ignore all
+	 * sched_clock() deltas that occured while we idled,
+	 * and use the PM-provided delta_ns to advance the
+	 * rq clock:
+	 */
+	__raw_spin_lock(&scd->lock);
+	scd->prev_raw = now;
+	scd->clock += delta_ns;
+	__raw_spin_unlock(&scd->lock);
+
+	touch_softlockup_watchdog();
+}
+EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
+
+#endif
+
+/*
+ * Scheduler clock - returns current time in nanosec units.
+ * This is default implementation.
+ * Architectures and sub-architectures can override this.
+ */
+unsigned long long __attribute__((weak)) sched_clock(void)
+{
+	return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
+}