1 files changed, 481 insertions, 0 deletions
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
new file mode 100644
index 000000000..e3e3b979f
--- /dev/null
+++ b/kernel/sched/clock.c
@@ -0,0 +1,481 @@
+/*
+ * sched_clock() for unstable CPU clocks
+ *
+ *  Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra
+ *
+ *  Updates and enhancements:
+ *    Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
+ *
+ * Based on code by:
+ *   Ingo Molnar <mingo@redhat.com>
+ *   Guillaume Chazarain <guichaz@gmail.com>
+ *
+ *
+ * What this file implements:
+ *
+ * cpu_clock(i) provides a fast (execution time) high resolution
+ * clock with bounded drift between CPUs. The value of cpu_clock(i)
+ * is monotonic for constant i. The timestamp returned is in nanoseconds.
+ *
+ * ######################### BIG FAT WARNING ##########################
+ * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
+ * # go backwards !!                                                  #
+ * ####################################################################
+ *
+ * There is no strict promise about the base, although it tends to start
+ * at 0 on boot (but people really shouldn't rely on that).
+ *
+ * cpu_clock(i)       -- can be used from any context, including NMI.
+ * local_clock()      -- is cpu_clock() on the current CPU.
+ *
+ * sched_clock_cpu(i)
+ *
+ * How it is implemented:
+ *
+ * The implementation either uses sched_clock() when
+ * !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the
+ * sched_clock() is assumed to provide these properties (mostly it means
+ * the architecture provides a globally synchronized highres time source).
+ *
+ * Otherwise it tries to create a semi stable clock from a mixture of other
+ * clocks, including:
+ *
+ *  - GTOD (clock monotomic)
+ *  - sched_clock()
+ *  - explicit idle events
+ *
+ * We use GTOD as base and use sched_clock() deltas to improve resolution. The
+ * deltas are filtered to provide monotonicity and keeping it within an
+ * expected window.
+ *
+ * Furthermore, explicit sleep and wakeup hooks allow us to account for time
+ * that is otherwise invisible (TSC gets stopped).
+ *
+ */
+#include "sched.h"
+#include <linux/sched_clock.h>
+
+/*
+ * Scheduler clock - returns current time in nanosec units.
+ * This is default implementation.
+ * Architectures and sub-architectures can override this.
+ */
+unsigned long long __weak sched_clock(void)
+{
+	return (unsigned long long)(jiffies - INITIAL_JIFFIES)
+					* (NSEC_PER_SEC / HZ);
+}
+EXPORT_SYMBOL_GPL(sched_clock);
+
+static DEFINE_STATIC_KEY_FALSE(sched_clock_running);
+
+#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+/*
+ * We must start with !__sched_clock_stable because the unstable -> stable
+ * transition is accurate, while the stable -> unstable transition is not.
+ *
+ * Similarly we start with __sched_clock_stable_early, thereby assuming we
+ * will become stable, such that there's only a single 1 -> 0 transition.
+ */
+static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable);
+static int __sched_clock_stable_early = 1;
+
+/*
+ * We want: ktime_get_ns() + __gtod_offset == sched_clock() + __sched_clock_offset
+ */
+__read_mostly u64 __sched_clock_offset;
+static __read_mostly u64 __gtod_offset;
+
+struct sched_clock_data {
+	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 this_cpu_ptr(&sched_clock_data);
+}
+
+static inline struct sched_clock_data *cpu_sdc(int cpu)
+{
+	return &per_cpu(sched_clock_data, cpu);
+}
+
+int sched_clock_stable(void)
+{
+	return static_branch_likely(&__sched_clock_stable);
+}
+
+static void __scd_stamp(struct sched_clock_data *scd)
+{
+	scd->tick_gtod = ktime_get_ns();
+	scd->tick_raw = sched_clock();
+}
+
+static void __set_sched_clock_stable(void)
+{
+	struct sched_clock_data *scd;
+
+	/*
+	 * Since we're still unstable and the tick is already running, we have
+	 * to disable IRQs in order to get a consistent scd->tick* reading.
+	 */
+	local_irq_disable();
+	scd = this_scd();
+	/*
+	 * Attempt to make the (initial) unstable->stable transition continuous.
+	 */
+	__sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw);
+	local_irq_enable();
+
+	printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n",
+			scd->tick_gtod, __gtod_offset,
+			scd->tick_raw,  __sched_clock_offset);
+
+	static_branch_enable(&__sched_clock_stable);
+	tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);
+}
+
+/*
+ * If we ever get here, we're screwed, because we found out -- typically after
+ * the fact -- that TSC wasn't good. This means all our clocksources (including
+ * ktime) could have reported wrong values.
+ *
+ * What we do here is an attempt to fix up and continue sort of where we left
+ * off in a coherent manner.
+ *
+ * The only way to fully avoid random clock jumps is to boot with:
+ * "tsc=unstable".
+ */
+static void __sched_clock_work(struct work_struct *work)
+{
+	struct sched_clock_data *scd;
+	int cpu;
+
+	/* take a current timestamp and set 'now' */
+	preempt_disable();
+	scd = this_scd();
+	__scd_stamp(scd);
+	scd->clock = scd->tick_gtod + __gtod_offset;
+	preempt_enable();
+
+	/* clone to all CPUs */
+	for_each_possible_cpu(cpu)
+		per_cpu(sched_clock_data, cpu) = *scd;
+
+	printk(KERN_WARNING "TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.\n");
+	printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n",
+			scd->tick_gtod, __gtod_offset,
+			scd->tick_raw,  __sched_clock_offset);
+
+	static_branch_disable(&__sched_clock_stable);
+}
+
+static DECLARE_WORK(sched_clock_work, __sched_clock_work);
+
+static void __clear_sched_clock_stable(void)
+{
+	if (!sched_clock_stable())
+		return;
+
+	tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
+	schedule_work(&sched_clock_work);
+}
+
+void clear_sched_clock_stable(void)
+{
+	__sched_clock_stable_early = 0;
+
+	smp_mb(); /* matches sched_clock_init_late() */
+
+	if (static_key_count(&sched_clock_running.key) == 2)
+		__clear_sched_clock_stable();
+}
+
+static void __sched_clock_gtod_offset(void)
+{
+	struct sched_clock_data *scd = this_scd();
+
+	__scd_stamp(scd);
+	__gtod_offset = (scd->tick_raw + __sched_clock_offset) - scd->tick_gtod;
+}
+
+void __init sched_clock_init(void)
+{
+	/*
+	 * Set __gtod_offset such that once we mark sched_clock_running,
+	 * sched_clock_tick() continues where sched_clock() left off.
+	 *
+	 * Even if TSC is buggered, we're still UP at this point so it
+	 * can't really be out of sync.
+	 */
+	local_irq_disable();
+	__sched_clock_gtod_offset();
+	local_irq_enable();
+
+	static_branch_inc(&sched_clock_running);
+}
+/*
+ * We run this as late_initcall() such that it runs after all built-in drivers,
+ * notably: acpi_processor and intel_idle, which can mark the TSC as unstable.
+ */
+static int __init sched_clock_init_late(void)
+{
+	static_branch_inc(&sched_clock_running);
+	/*
+	 * Ensure that it is impossible to not do a static_key update.
+	 *
+	 * Either {set,clear}_sched_clock_stable() must see sched_clock_running
+	 * and do the update, or we must see their __sched_clock_stable_early
+	 * and do the update, or both.
+	 */
+	smp_mb(); /* matches {set,clear}_sched_clock_stable() */
+
+	if (__sched_clock_stable_early)
+		__set_sched_clock_stable();
+
+	return 0;
+}
+late_initcall(sched_clock_init_late);
+
+/*
+ * min, max except they take wrapping into account
+ */
+
+static inline u64 wrap_min(u64 x, u64 y)
+{
+	return (s64)(x - y) < 0 ? x : y;
+}
+
+static inline u64 wrap_max(u64 x, u64 y)
+{
+	return (s64)(x - y) > 0 ? x : y;
+}
+
+/*
+ * update the percpu scd from the raw @now value
+ *
+ *  - filter out backward motion
+ *  - use the GTOD tick value to create a window to filter crazy TSC values
+ */
+static u64 sched_clock_local(struct sched_clock_data *scd)
+{
+	u64 now, clock, old_clock, min_clock, max_clock, gtod;
+	s64 delta;
+
+again:
+	now = sched_clock();
+	delta = now - scd->tick_raw;
+	if (unlikely(delta < 0))
+		delta = 0;
+
+	old_clock = scd->clock;
+
+	/*
+	 * scd->clock = clamp(scd->tick_gtod + delta,
+	 *		      max(scd->tick_gtod, scd->clock),
+	 *		      scd->tick_gtod + TICK_NSEC);
+	 */
+
+	gtod = scd->tick_gtod + __gtod_offset;
+	clock = gtod + delta;
+	min_clock = wrap_max(gtod, old_clock);
+	max_clock = wrap_max(old_clock, gtod + TICK_NSEC);
+
+	clock = wrap_max(clock, min_clock);
+	clock = wrap_min(clock, max_clock);
+
+	if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
+		goto again;
+
+	return clock;
+}
+
+static u64 sched_clock_remote(struct sched_clock_data *scd)
+{
+	struct sched_clock_data *my_scd = this_scd();
+	u64 this_clock, remote_clock;
+	u64 *ptr, old_val, val;
+
+#if BITS_PER_LONG != 64
+again:
+	/*
+	 * Careful here: The local and the remote clock values need to
+	 * be read out atomic as we need to compare the values and
+	 * then update either the local or the remote side. So the
+	 * cmpxchg64 below only protects one readout.
+	 *
+	 * We must reread via sched_clock_local() in the retry case on
+	 * 32-bit kernels as an NMI could use sched_clock_local() via the
+	 * tracer and hit between the readout of
+	 * the low 32-bit and the high 32-bit portion.
+	 */
+	this_clock = sched_clock_local(my_scd);
+	/*
+	 * We must enforce atomic readout on 32-bit, otherwise the
+	 * update on the remote CPU can hit inbetween the readout of
+	 * the low 32-bit and the high 32-bit portion.
+	 */
+	remote_clock = cmpxchg64(&scd->clock, 0, 0);
+#else
+	/*
+	 * On 64-bit kernels the read of [my]scd->clock is atomic versus the
+	 * update, so we can avoid the above 32-bit dance.
+	 */
+	sched_clock_local(my_scd);
+again:
+	this_clock = my_scd->clock;
+	remote_clock = scd->clock;
+#endif
+
+	/*
+	 * Use the opportunity that we have both locks
+	 * taken to couple the two clocks: we take the
+	 * larger time as the latest time for both
+	 * runqueues. (this creates monotonic movement)
+	 */
+	if (likely((s64)(remote_clock - this_clock) < 0)) {
+		ptr = &scd->clock;
+		old_val = remote_clock;
+		val = this_clock;
+	} else {
+		/*
+		 * Should be rare, but possible:
+		 */
+		ptr = &my_scd->clock;
+		old_val = this_clock;
+		val = remote_clock;
+	}
+
+	if (cmpxchg64(ptr, old_val, val) != old_val)
+		goto again;
+
+	return val;
+}
+
+/*
+ * Similar to cpu_clock(), but requires local IRQs to be disabled.
+ *
+ * See cpu_clock().
+ */
+u64 sched_clock_cpu(int cpu)
+{
+	struct sched_clock_data *scd;
+	u64 clock;
+
+	if (sched_clock_stable())
+		return sched_clock() + __sched_clock_offset;
+
+	if (!static_branch_unlikely(&sched_clock_running))
+		return sched_clock();
+
+	preempt_disable_notrace();
+	scd = cpu_sdc(cpu);
+
+	if (cpu != smp_processor_id())
+		clock = sched_clock_remote(scd);
+	else
+		clock = sched_clock_local(scd);
+	preempt_enable_notrace();
+
+	return clock;
+}
+EXPORT_SYMBOL_GPL(sched_clock_cpu);
+
+void sched_clock_tick(void)
+{
+	struct sched_clock_data *scd;
+
+	if (sched_clock_stable())
+		return;
+
+	if (!static_branch_unlikely(&sched_clock_running))
+		return;
+
+	lockdep_assert_irqs_disabled();
+
+	scd = this_scd();
+	__scd_stamp(scd);
+	sched_clock_local(scd);
+}
+
+void sched_clock_tick_stable(void)
+{
+	if (!sched_clock_stable())
+		return;
+
+	/*
+	 * Called under watchdog_lock.
+	 *
+	 * The watchdog just found this TSC to (still) be stable, so now is a
+	 * good moment to update our __gtod_offset. Because once we find the
+	 * TSC to be unstable, any computation will be computing crap.
+	 */
+	local_irq_disable();
+	__sched_clock_gtod_offset();
+	local_irq_enable();
+}
+
+/*
+ * 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; resync with ktime.
+ */
+void sched_clock_idle_wakeup_event(void)
+{
+	unsigned long flags;
+
+	if (sched_clock_stable())
+		return;
+
+	if (unlikely(timekeeping_suspended))
+		return;
+
+	local_irq_save(flags);
+	sched_clock_tick();
+	local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
+
+#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
+
+void __init sched_clock_init(void)
+{
+	static_branch_inc(&sched_clock_running);
+	local_irq_disable();
+	generic_sched_clock_init();
+	local_irq_enable();
+}
+
+u64 sched_clock_cpu(int cpu)
+{
+	if (!static_branch_unlikely(&sched_clock_running))
+		return 0;
+
+	return sched_clock();
+}
+
+#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
+
+/*
+ * Running clock - returns the time that has elapsed while a guest has been
+ * running.
+ * On a guest this value should be local_clock minus the time the guest was
+ * suspended by the hypervisor (for any reason).
+ * On bare metal this function should return the same as local_clock.
+ * Architectures and sub-architectures can override this.
+ */
+u64 __weak running_clock(void)
+{
+	return local_clock();
+}