// 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 prev_time */	if ((s64)(now - prev_time) < 0)		now = prev_time + 1; 	/*	 * 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 + 1; 		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);}