cregit-Linux how code gets into the kernel

Release 4.15 kernel/trace/trace_clock.c

Directory: kernel/trace
 * tracing clocks
 *  Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <>
 * 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; }


Ingo Molnar1246.15%125.00%
Peter Zijlstra1038.46%125.00%
Steven Rostedt415.38%250.00%

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(); }


Ingo Molnar1191.67%150.00%
Peter Zijlstra18.33%150.00%

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); }


Steven Rostedt1275.00%150.00%
Tony Luck425.00%150.00%

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; local_irq_save(flags); this_cpu = raw_smp_processor_id(); now = sched_clock_cpu(this_cpu); /* * If in an NMI context then dont risk lockups and return the * cpu_clock() time: */ if (unlikely(in_nmi())) goto out; arch_spin_lock(&trace_clock_struct.lock); /* * TODO: if this happens often then maybe we should reset * my_scd->clock to prev_time+1, to make sure * we start ticking with the local clock from now on? */ if ((s64)(now - trace_clock_struct.prev_time) < 0) now = trace_clock_struct.prev_time + 1; trace_clock_struct.prev_time = now; arch_spin_unlock(&trace_clock_struct.lock); out: local_irq_restore(flags); return now; }


Ingo Molnar8279.61%120.00%
Steven Rostedt1615.53%120.00%
Thomas Gleixner21.94%120.00%
Li Zefan21.94%120.00%
Namhyung Kim10.97%120.00%

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); }


Steven Rostedt17100.00%1100.00%

Overall Contributors

Ingo Molnar13653.33%210.00%
Steven Rostedt6826.67%525.00%
Jerry Snitselaar155.88%15.00%
Peter Zijlstra114.31%210.00%
Paul E. McKenney51.96%15.00%
Thomas Gleixner51.96%315.00%
Tony Luck51.96%15.00%
Dmitri Vorobiev31.18%15.00%
Frédéric Weisbecker31.18%15.00%
Li Zefan20.78%15.00%
Lucas De Marchi10.39%15.00%
Namhyung Kim10.39%15.00%
Directory: kernel/trace
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