1 files changed, 158 insertions, 0 deletions
diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
new file mode 100644
index 000000000..4702efb00
--- /dev/null
+++ b/kernel/trace/trace_clock.c
@@ -0,0 +1,158 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * tracing clocks
+ *
+ *  Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ *
+ * Implements 3 trace clock variants, with differing scalability/precision
+ * tradeoffs:
+ *
+ *  -   local: CPU-local trace clock
+ *  -  medium: scalable global clock with some jitter
+ *  -  global: globally monotonic, serialized clock
+ *
+ * Tracer plugins will chose a default from these clocks.
+ */
+#include <linux/spinlock.h>
+#include <linux/irqflags.h>
+#include <linux/hardirq.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/sched.h>
+#include <linux/sched/clock.h>
+#include <linux/ktime.h>
+#include <linux/trace_clock.h>
+
+/*
+ * trace_clock_local(): the simplest and least coherent tracing clock.
+ *
+ * Useful for tracing that does not cross to other CPUs nor
+ * does it go through idle events.
+ */
+u64 notrace trace_clock_local(void)
+{
+	u64 clock;
+
+	/*
+	 * sched_clock() is an architecture implemented, fast, scalable,
+	 * lockless clock. It is not guaranteed to be coherent across
+	 * CPUs, nor across CPU idle events.
+	 */
+	preempt_disable_notrace();
+	clock = sched_clock();
+	preempt_enable_notrace();
+
+	return clock;
+}
+EXPORT_SYMBOL_GPL(trace_clock_local);
+
+/*
+ * trace_clock(): 'between' trace clock. Not completely serialized,
+ * but not completely incorrect when crossing CPUs either.
+ *
+ * This is based on cpu_clock(), which will allow at most ~1 jiffy of
+ * jitter between CPUs. So it's a pretty scalable clock, but there
+ * can be offsets in the trace data.
+ */
+u64 notrace trace_clock(void)
+{
+	return local_clock();
+}
+EXPORT_SYMBOL_GPL(trace_clock);
+
+/*
+ * trace_jiffy_clock(): Simply use jiffies as a clock counter.
+ * Note that this use of jiffies_64 is not completely safe on
+ * 32-bit systems. But the window is tiny, and the effect if
+ * we are affected is that we will have an obviously bogus
+ * timestamp on a trace event - i.e. not life threatening.
+ */
+u64 notrace trace_clock_jiffies(void)
+{
+	return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
+}
+EXPORT_SYMBOL_GPL(trace_clock_jiffies);
+
+/*
+ * trace_clock_global(): special globally coherent trace clock
+ *
+ * It has higher overhead than the other trace clocks but is still
+ * an order of magnitude faster than GTOD derived hardware clocks.
+ *
+ * Used by plugins that need globally coherent timestamps.
+ */
+
+/* keep prev_time and lock in the same cacheline. */
+static struct {
+	u64 prev_time;
+	arch_spinlock_t lock;
+} trace_clock_struct ____cacheline_aligned_in_smp =
+	{
+		.lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
+	};
+
+u64 notrace trace_clock_global(void)
+{
+	unsigned long flags;
+	int this_cpu;
+	u64 now, prev_time;
+
+	raw_local_irq_save(flags);
+
+	this_cpu = raw_smp_processor_id();
+
+	/*
+	 * The global clock "guarantees" that the events are ordered
+	 * between CPUs. But if two events on two different CPUS call
+	 * trace_clock_global at roughly the same time, it really does
+	 * not matter which one gets the earlier time. Just make sure
+	 * that the same CPU will always show a monotonic clock.
+	 *
+	 * Use a read memory barrier to get the latest written
+	 * time that was recorded.
+	 */
+	smp_rmb();
+	prev_time = READ_ONCE(trace_clock_struct.prev_time);
+	now = sched_clock_cpu(this_cpu);
+
+	/* Make sure that now is always greater than or equal to prev_time */
+	if ((s64)(now - prev_time) < 0)
+		now = prev_time;
+
+	/*
+	 * If in an NMI context then dont risk lockups and simply return
+	 * the current time.
+	 */
+	if (unlikely(in_nmi()))
+		goto out;
+
+	/* Tracing can cause strange recursion, always use a try lock */
+	if (arch_spin_trylock(&trace_clock_struct.lock)) {
+		/* Reread prev_time in case it was already updated */
+		prev_time = READ_ONCE(trace_clock_struct.prev_time);
+		if ((s64)(now - prev_time) < 0)
+			now = prev_time;
+
+		trace_clock_struct.prev_time = now;
+
+		/* The unlock acts as the wmb for the above rmb */
+		arch_spin_unlock(&trace_clock_struct.lock);
+	}
+ out:
+	raw_local_irq_restore(flags);
+
+	return now;
+}
+EXPORT_SYMBOL_GPL(trace_clock_global);
+
+static atomic64_t trace_counter;
+
+/*
+ * trace_clock_counter(): simply an atomic counter.
+ * Use the trace_counter "counter" for cases where you do not care
+ * about timings, but are interested in strict ordering.
+ */
+u64 notrace trace_clock_counter(void)
+{
+	return atomic64_add_return(1, &trace_counter);
+}