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