/* * 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 __initsched_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);