linux/kernel/time/jiffies.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * This file contains the jiffies based clocksource.
 *
 * Copyright (C) 2004, 2005 IBM, John Stultz ([email protected])
 */
#include <linux/clocksource.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/init.h>

#include "timekeeping.h"
#include "tick-internal.h"


static u64 jiffies_read(struct clocksource *cs)
{ … }

/*
 * The Jiffies based clocksource is the lowest common
 * denominator clock source which should function on
 * all systems. It has the same coarse resolution as
 * the timer interrupt frequency HZ and it suffers
 * inaccuracies caused by missed or lost timer
 * interrupts and the inability for the timer
 * interrupt hardware to accurately tick at the
 * requested HZ value. It is also not recommended
 * for "tick-less" systems.
 */
static struct clocksource clocksource_jiffies = …;

__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(…);
__cacheline_aligned_in_smp seqcount_raw_spinlock_t jiffies_seq = …;

#if (BITS_PER_LONG < 64)
u64 get_jiffies_64(void)
{
	unsigned int seq;
	u64 ret;

	do {
		seq = read_seqcount_begin(&jiffies_seq);
		ret = jiffies_64;
	} while (read_seqcount_retry(&jiffies_seq, seq));
	return ret;
}
EXPORT_SYMBOL(get_jiffies_64);
#endif

EXPORT_SYMBOL(…);

static int __init init_jiffies_clocksource(void)
{ … }

core_initcall(init_jiffies_clocksource);

struct clocksource * __init __weak clocksource_default_clock(void)
{ … }

static struct clocksource refined_jiffies;

int register_refined_jiffies(long cycles_per_second)
{ … }