kernel/time/sched_clock.c - third_party/linux - Git at Google

 /*
  * 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/sched/clock.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);
 }

 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;
 }

 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;
 }

 /*
  * 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);
 }

 /*
  * 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);
 }

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

 	return HRTIMER_RESTART;
 }

 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);

 	if (sched_clock_timer.function != NULL) {
 		/* update timeout for clock wrap */
 		hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
 	}

 	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);
 }

 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);
 }

 /*
  * 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;
 }

 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;
 }

 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;
 }

 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;
 }
 device_initcall(sched_clock_syscore_init);
	/*
	* 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/sched/clock.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);
	}

	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;
	}

	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;
	}

	/*
	* 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);
	}

	/*
	* 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);
	}

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

	return HRTIMER_RESTART;
	}

	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);

	if (sched_clock_timer.function != NULL) {
	/* update timeout for clock wrap */
	hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
	}

	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);
	}

	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);
	}

	/*
	* 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;
	}

	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;
	}

	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;
	}

	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;
	}
	device_initcall(sched_clock_syscore_init);