Release 4.7 kernel/time/sched_clock.c

/*
 * sched_clock.c: Generic sched_clock() support, to extend low level
 *                hardware time counters to full 64-bit ns values.
 *
 * 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>
#include <linux/bitops.h>

/**
 * struct clock_read_data - data required to read from sched_clock()
 *
 * @epoch_ns:           sched_clock() value at last update
 * @epoch_cyc:          Clock cycle value at last update.
 * @sched_clock_mask:   Bitmask for two's complement subtraction of non 64bit
 *                      clocks.
 * @read_sched_clock:   Current clock source (or dummy source when suspended).
 * @mult:               Multipler for scaled math conversion.
 * @shift:              Shift value for scaled math conversion.
 *
 * Care must be taken when updating this structure; it is read by
 * some very hot code paths. It occupies <=40 bytes and, when combined
 * with the seqcount used to synchronize access, comfortably fits into
 * a 64 byte cache line.
 */

struct clock_read_data {
	
u64 epoch_ns;
	
u64 epoch_cyc;
	
u64 sched_clock_mask;
	
u64 (*read_sched_clock)(void);
	
u32 mult;
	
u32 shift;
};

/**
 * struct clock_data - all data needed for sched_clock() (including
 *                     registration of a new clock source)
 *
 * @seq:                Sequence counter for protecting updates. The lowest
 *                      bit is the index for @read_data.
 * @read_data:          Data required to read from sched_clock.
 * @wrap_kt:            Duration for which clock can run before wrapping.
 * @rate:               Tick rate of the registered clock.
 * @actual_read_sched_clock: Registered hardware level clock read function.
 *
 * The ordering of this structure has been chosen to optimize cache
 * performance. In particular 'seq' and 'read_data[0]' (combined) should fit
 * into a single 64-byte cache line.
 */

struct clock_data {
	
seqcount_t		seq;
	
struct clock_read_data	read_data[2];
	
ktime_t			wrap_kt;
	
unsigned long		rate;

	
u64 (*actual_read_sched_clock)(void);
};


static struct hrtimer sched_clock_timer;

static int irqtime = -1;

core_param(irqtime, irqtime, int, 0400);



static u64 notrace jiffy_sched_clock_read(void)
{
	/*
         * We don't need to use get_jiffies_64 on 32-bit arches here
         * because we register with BITS_PER_LONG
         */
	return (u64)(jiffies - INITIAL_JIFFIES);
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
marc zyngier
marc zyngier
16
80.00%
1
33.33%
stephen boyd
stephen boyd
3
15.00%
1
33.33%
russell king
russell king
1
5.00%
1
33.33%
Total
20
100.00%
3
100.00%


static struct clock_data cd ____cacheline_aligned = {
	.read_data[0] = { .mult = NSEC_PER_SEC / HZ,
			  .read_sched_clock = jiffy_sched_clock_read, },
	.actual_read_sched_clock = jiffy_sched_clock_read,
};



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

Contributors
Person
Tokens
Prop
Commits
CommitProp
marc zyngier
marc zyngier
25
96.15%
1
50.00%
stephen boyd
stephen boyd
1
3.85%
1
50.00%
Total
26
100.00%
2
100.00%



unsigned long long notrace sched_clock(void)
{
	u64 cyc, res;
	unsigned long seq;
	struct clock_read_data *rd;

	do {
		seq = raw_read_seqcount(&cd.seq);
		rd = cd.read_data + (seq & 1);

		cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
		      rd->sched_clock_mask;
		res = rd->epoch_ns + cyc_to_ns(cyc, rd->mult, rd->shift);
	} while (read_seqcount_retry(&cd.seq, seq));

	return res;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
daniel thompson
daniel thompson
54
53.47%
4
44.44%
stephen boyd
stephen boyd
27
26.73%
4
44.44%
marc zyngier
marc zyngier
20
19.80%
1
11.11%
Total
101
100.00%
9
100.00%

/*
 * Updating the data required to read the clock.
 *
 * sched_clock() will never observe mis-matched data even if called from
 * an NMI. We do this by maintaining an odd/even copy of the data and
 * steering sched_clock() to one or the other using a sequence counter.
 * In order to preserve the data cache profile of sched_clock() as much
 * as possible the system reverts back to the even copy when the update
 * completes; the odd copy is used *only* during an update.
 */


static void update_clock_read_data(struct clock_read_data *rd)
{
	/* update the backup (odd) copy with the new data */
	cd.read_data[1] = *rd;

	/* steer readers towards the odd copy */
	raw_write_seqcount_latch(&cd.seq);

	/* now its safe for us to update the normal (even) copy */
	cd.read_data[0] = *rd;

	/* switch readers back to the even copy */
	raw_write_seqcount_latch(&cd.seq);
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
daniel thompson
daniel thompson
51
100.00%
1
100.00%
Total
51
100.00%
1
100.00%

/*
 * Atomically update the sched_clock() epoch.
 */


static void update_sched_clock(void)
{
	u64 cyc;
	u64 ns;
	struct clock_read_data rd;

	rd = cd.read_data[0];

	cyc = cd.actual_read_sched_clock();
	ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);

	rd.epoch_ns = ns;
	rd.epoch_cyc = cyc;

	update_clock_read_data(&rd);
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
marc zyngier
marc zyngier
44
54.32%
1
14.29%
daniel thompson
daniel thompson
32
39.51%
3
42.86%
stephen boyd
stephen boyd
4
4.94%
2
28.57%
joonsoo kim
joonsoo kim
1
1.23%
1
14.29%
Total
81
100.00%
7
100.00%



static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
{
	update_sched_clock();
	hrtimer_forward_now(hrt, cd.wrap_kt);

	return HRTIMER_RESTART;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
stephen boyd
stephen boyd
17
62.96%
1
50.00%
russell king
russell king
10
37.04%
1
50.00%
Total
27
100.00%
2
100.00%


void __init

sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)
{
	u64 res, wrap, new_mask, new_epoch, cyc, ns;
	u32 new_mult, new_shift;
	unsigned long r;
	char r_unit;
	struct clock_read_data rd;

	if (cd.rate > rate)
		return;

	WARN_ON(!irqs_disabled());

	/* Calculate the mult/shift to convert counter ticks to ns. */
	clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);

	new_mask = CLOCKSOURCE_MASK(bits);
	cd.rate = rate;

	/* Calculate how many nanosecs until we risk wrapping */
	wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);
	cd.wrap_kt = ns_to_ktime(wrap);

	rd = cd.read_data[0];

	/* Update epoch for new counter and update 'epoch_ns' from old counter*/
	new_epoch = read();
	cyc = cd.actual_read_sched_clock();
	ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
	cd.actual_read_sched_clock = read;

	rd.read_sched_clock	= read;
	rd.sched_clock_mask	= new_mask;
	rd.mult			= new_mult;
	rd.shift		= new_shift;
	rd.epoch_cyc		= new_epoch;
	rd.epoch_ns		= ns;

	update_clock_read_data(&rd);

	r = rate;
	if (r >= 4000000) {
		r /= 1000000;
		r_unit = 'M';
	} else {
		if (r >= 1000) {
			r /= 1000;
			r_unit = 'k';
		} else {
			r_unit = ' ';
		}
	}

	/* Calculate the ns resolution of this counter */
	res = cyc_to_ns(1ULL, new_mult, new_shift);

	pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
		bits, r, r_unit, res, wrap);

	/* Enable IRQ time accounting if we have a fast enough sched_clock() */
	if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
		enable_sched_clock_irqtime();

	pr_debug("Registered %pF as sched_clock source\n", read);
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
stephen boyd
stephen boyd
107
33.33%
3
23.08%
russell king
russell king
104
32.40%
2
15.38%
daniel thompson
daniel thompson
55
17.13%
4
30.77%
marc zyngier
marc zyngier
32
9.97%
1
7.69%
rob herring
rob herring
11
3.43%
1
7.69%
ingo molnar
ingo molnar
10
3.12%
1
7.69%
john stultz
john stultz
2
0.62%
1
7.69%
Total
321
100.00%
13
100.00%



void __init sched_clock_postinit(void)
{
	/*
         * If no sched_clock() function has been provided at that point,
         * make it the final one one.
         */
	if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
		sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);

	update_sched_clock();

	/*
         * Start the timer to keep sched_clock() properly updated and
         * sets the initial epoch.
         */
	hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
	sched_clock_timer.function = sched_clock_poll;
	hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
stephen boyd
stephen boyd
28
48.28%
2
28.57%
russell king
russell king
14
24.14%
1
14.29%
marc zyngier
marc zyngier
12
20.69%
1
14.29%
daniel thompson
daniel thompson
3
5.17%
2
28.57%
ingo molnar
ingo molnar
1
1.72%
1
14.29%
Total
58
100.00%
7
100.00%

/*
 * Clock read function for use when the clock is suspended.
 *
 * This function makes it appear to sched_clock() as if the clock
 * stopped counting at its last update.
 *
 * This function must only be called from the critical
 * section in sched_clock(). It relies on the read_seqcount_retry()
 * at the end of the critical section to be sure we observe the
 * correct copy of 'epoch_cyc'.
 */


static u64 notrace suspended_sched_clock_read(void)
{
	unsigned long seq = raw_read_seqcount(&cd.seq);

	return cd.read_data[seq & 1].epoch_cyc;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
daniel thompson
daniel thompson
33
100.00%
2
100.00%
Total
33
100.00%
2
100.00%



static int sched_clock_suspend(void)
{
	struct clock_read_data *rd = &cd.read_data[0];

	update_sched_clock();
	hrtimer_cancel(&sched_clock_timer);
	rd->read_sched_clock = suspended_sched_clock_read;

	return 0;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
daniel thompson
daniel thompson
17
43.59%
3
42.86%
russell king
russell king
15
38.46%
1
14.29%
stephen boyd
stephen boyd
5
12.82%
2
28.57%
colin cross
colin cross
2
5.13%
1
14.29%
Total
39
100.00%
7
100.00%



static void sched_clock_resume(void)
{
	struct clock_read_data *rd = &cd.read_data[0];

	rd->epoch_cyc = cd.actual_read_sched_clock();
	hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
	rd->read_sched_clock = cd.actual_read_sched_clock;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
daniel thompson
daniel thompson
22
44.00%
3
60.00%
colin cross
colin cross
16
32.00%
1
20.00%
stephen boyd
stephen boyd
12
24.00%
1
20.00%
Total
50
100.00%
5
100.00%


static struct syscore_ops sched_clock_ops = {
	.suspend	= sched_clock_suspend,
	.resume		= sched_clock_resume,
};



static int __init sched_clock_syscore_init(void)
{
	register_syscore_ops(&sched_clock_ops);

	return 0;
}
Contributors
Person
Tokens
Prop
Commits
CommitProp
russell king
russell king
18
100.00%
1
100.00%
Total
18
100.00%
1
100.00%


device_initcall(sched_clock_syscore_init);
Overall Contributors
Person
Tokens
Prop
Commits
CommitProp
daniel thompson
daniel thompson
340
33.83%
4
17.39%
russell king
russell king
224
22.29%
4
17.39%
stephen boyd
stephen boyd
220
21.89%
9
39.13%
marc zyngier
marc zyngier
166
16.52%
1
4.35%
colin cross
colin cross
23
2.29%
1
4.35%
ingo molnar
ingo molnar
17
1.69%
1
4.35%
rob herring
rob herring
12
1.19%
1
4.35%
john stultz
john stultz
2
0.20%
1
4.35%
joonsoo kim
joonsoo kim
1
0.10%
1
4.35%
Total
1005
100.00%
23
100.00%
  
Directory: kernel/time

Information contained on this website is for historical information purposes only and does not indicate or represent copyright ownership.