1/*
  2 * sched_clock.c: support for extending counters to full 64-bit ns counter
  3 *
  4 * This program is free software; you can redistribute it and/or modify
  5 * it under the terms of the GNU General Public License version 2 as
  6 * published by the Free Software Foundation.
  7 */
  8#include <linux/clocksource.h>
  9#include <linux/init.h>
 10#include <linux/jiffies.h>
 11#include <linux/ktime.h>
 12#include <linux/kernel.h>
 13#include <linux/moduleparam.h>
 14#include <linux/sched.h>
 15#include <linux/syscore_ops.h>
 16#include <linux/hrtimer.h>
 17#include <linux/sched_clock.h>
 18#include <linux/seqlock.h>
 19#include <linux/bitops.h>
 20
 21struct clock_data {
 22	ktime_t wrap_kt;
 23	u64 epoch_ns;
 24	u64 epoch_cyc;
 25	seqcount_t seq;
 26	unsigned long rate;
 27	u32 mult;
 28	u32 shift;
 29	bool suspended;
 30};
 31
 32static struct hrtimer sched_clock_timer;
 33static int irqtime = -1;
 34
 35core_param(irqtime, irqtime, int, 0400);
 36
 37static struct clock_data cd = {
 38	.mult	= NSEC_PER_SEC / HZ,
 39};
 40
 41static u64 __read_mostly sched_clock_mask;
 42
 43static u64 notrace jiffy_sched_clock_read(void)
 44{
 45	/*
 46	 * We don't need to use get_jiffies_64 on 32-bit arches here
 47	 * because we register with BITS_PER_LONG
 48	 */
 49	return (u64)(jiffies - INITIAL_JIFFIES);
 50}
 51
 52static u32 __read_mostly (*read_sched_clock_32)(void);
 53
 54static u64 notrace read_sched_clock_32_wrapper(void)
 55{
 56	return read_sched_clock_32();
 57}
 58
 59static u64 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
 60
 61static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
 62{
 63	return (cyc * mult) >> shift;
 64}
 65
 66unsigned long long notrace sched_clock(void)
 67{
 68	u64 epoch_ns;
 69	u64 epoch_cyc;
 70	u64 cyc;
 71	unsigned long seq;
 72
 73	if (cd.suspended)
 74		return cd.epoch_ns;
 75
 76	do {
 77		seq = raw_read_seqcount_begin(&cd.seq);
 78		epoch_cyc = cd.epoch_cyc;
 79		epoch_ns = cd.epoch_ns;
 80	} while (read_seqcount_retry(&cd.seq, seq));
 81
 82	cyc = read_sched_clock();
 83	cyc = (cyc - epoch_cyc) & sched_clock_mask;
 84	return epoch_ns + cyc_to_ns(cyc, cd.mult, cd.shift);
 85}
 86
 87/*
 88 * Atomically update the sched_clock epoch.
 89 */
 90static void notrace update_sched_clock(void)
 91{
 92	unsigned long flags;
 93	u64 cyc;
 94	u64 ns;
 95
 96	cyc = read_sched_clock();
 97	ns = cd.epoch_ns +
 98		cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
 99			  cd.mult, cd.shift);
100
101	raw_local_irq_save(flags);
102	raw_write_seqcount_begin(&cd.seq);
103	cd.epoch_ns = ns;
104	cd.epoch_cyc = cyc;
105	raw_write_seqcount_end(&cd.seq);
106	raw_local_irq_restore(flags);
107}
108
109static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
110{
111	update_sched_clock();
112	hrtimer_forward_now(hrt, cd.wrap_kt);
113	return HRTIMER_RESTART;
114}
115
116void __init sched_clock_register(u64 (*read)(void), int bits,
117				 unsigned long rate)
118{
119	u64 res, wrap, new_mask, new_epoch, cyc, ns;
120	u32 new_mult, new_shift;
121	ktime_t new_wrap_kt;
122	unsigned long r;
123	char r_unit;
124
125	if (cd.rate > rate)
126		return;
127
128	WARN_ON(!irqs_disabled());
129
130	/* calculate the mult/shift to convert counter ticks to ns. */
131	clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
132
133	new_mask = CLOCKSOURCE_MASK(bits);
134
135	/* calculate how many ns until we wrap */
136	wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask);
137	new_wrap_kt = ns_to_ktime(wrap - (wrap >> 3));
138
139	/* update epoch for new counter and update epoch_ns from old counter*/
140	new_epoch = read();
141	cyc = read_sched_clock();
142	ns = cd.epoch_ns + cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
143			  cd.mult, cd.shift);
144
145	raw_write_seqcount_begin(&cd.seq);
146	read_sched_clock = read;
147	sched_clock_mask = new_mask;
148	cd.rate = rate;
149	cd.wrap_kt = new_wrap_kt;
150	cd.mult = new_mult;
151	cd.shift = new_shift;
152	cd.epoch_cyc = new_epoch;
153	cd.epoch_ns = ns;
154	raw_write_seqcount_end(&cd.seq);
155
156	r = rate;
157	if (r >= 4000000) {
158		r /= 1000000;
159		r_unit = 'M';
160	} else if (r >= 1000) {
161		r /= 1000;
162		r_unit = 'k';
163	} else
164		r_unit = ' ';
165
166	/* calculate the ns resolution of this counter */
167	res = cyc_to_ns(1ULL, new_mult, new_shift);
168
169	pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
170		bits, r, r_unit, res, wrap);
171
172	/* Enable IRQ time accounting if we have a fast enough sched_clock */
173	if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
174		enable_sched_clock_irqtime();
175
176	pr_debug("Registered %pF as sched_clock source\n", read);
177}
178
179void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
180{
181	read_sched_clock_32 = read;
182	sched_clock_register(read_sched_clock_32_wrapper, bits, rate);
183}
184
185void __init sched_clock_postinit(void)
186{
187	/*
188	 * If no sched_clock function has been provided at that point,
189	 * make it the final one one.
190	 */
191	if (read_sched_clock == jiffy_sched_clock_read)
192		sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
193
194	update_sched_clock();
195
196	/*
197	 * Start the timer to keep sched_clock() properly updated and
198	 * sets the initial epoch.
199	 */
200	hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
201	sched_clock_timer.function = sched_clock_poll;
202	hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
203}
204
205static int sched_clock_suspend(void)
206{
207	sched_clock_poll(&sched_clock_timer);
208	cd.suspended = true;
209	return 0;
210}
211
212static void sched_clock_resume(void)
213{
214	cd.epoch_cyc = read_sched_clock();
215	cd.suspended = false;
216}
217
218static struct syscore_ops sched_clock_ops = {
219	.suspend = sched_clock_suspend,
220	.resume = sched_clock_resume,
221};
222
223static int __init sched_clock_syscore_init(void)
224{
225	register_syscore_ops(&sched_clock_ops);
226	return 0;
227}
228device_initcall(sched_clock_syscore_init);