sched_clock.c

/*
 * sched_clock.c: support for extending counters to full 64-bit ns counter
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/ktime.h>
#include <linux/kernel.h>
#include <linux/moduleparam.h>
#include <linux/sched.h>
#include <linux/syscore_ops.h>
#include <linux/hrtimer.h>
#include <linux/sched_clock.h>
#include <linux/seqlock.h>

struct clock_data {
	ktime_t wrap_kt;
	u64 epoch_ns;
	u32 epoch_cyc;
	seqcount_t seq;
	unsigned long rate;
	u32 mult;
	u32 shift;
	bool suspended;
};

static struct hrtimer sched_clock_timer;
static int irqtime = -1;

core_param(irqtime, irqtime, int, 0400);

static struct clock_data cd = {
	.mult	= NSEC_PER_SEC / HZ,
};

static u32 __read_mostly sched_clock_mask = 0xffffffff;

static u32 notrace jiffy_sched_clock_read(void)
{
	return (u32)(jiffies - INITIAL_JIFFIES);
}

static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;

static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
{
	return (cyc * mult) >> shift;
}

static unsigned long long notrace sched_clock_32(void)
{
	u64 epoch_ns;
	u32 epoch_cyc;
	u32 cyc;
	unsigned long seq;

	if (cd.suspended)
		return cd.epoch_ns;

	do {
		seq = read_seqcount_begin(&cd.seq);
		epoch_cyc = cd.epoch_cyc;
		epoch_ns = cd.epoch_ns;
	} while (read_seqcount_retry(&cd.seq, seq));

	cyc = read_sched_clock();