2 * sched_clock.c: support for extending counters to full 64-bit ns counter
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.
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>
32 static struct hrtimer sched_clock_timer;
33 static int irqtime = -1;
35 core_param(irqtime, irqtime, int, 0400);
37 static struct clock_data cd = {
38 .mult = NSEC_PER_SEC / HZ,
41 static u64 __read_mostly sched_clock_mask;
43 static u64 notrace jiffy_sched_clock_read(void)
46 * We don't need to use get_jiffies_64 on 32-bit arches here
47 * because we register with BITS_PER_LONG
49 return (u64)(jiffies - INITIAL_JIFFIES);
52 static u32 __read_mostly (*read_sched_clock_32)(void);
54 static u64 notrace read_sched_clock_32_wrapper(void)
56 return read_sched_clock_32();
59 static u64 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
61 static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
63 return (cyc * mult) >> shift;
66 unsigned long long notrace sched_clock(void)
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));
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);
88 * Atomically update the sched_clock epoch.
90 static void notrace update_sched_clock(void)
96 cyc = read_sched_clock();
98 cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
101 raw_local_irq_save(flags);
102 raw_write_seqcount_begin(&cd.seq);
105 raw_write_seqcount_end(&cd.seq);
106 raw_local_irq_restore(flags);
109 static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
111 update_sched_clock();
112 hrtimer_forward_now(hrt, cd.wrap_kt);
113 return HRTIMER_RESTART;
116 void __init sched_clock_register(u64 (*read)(void), int bits,
119 u64 res, wrap, new_mask, new_epoch, cyc, ns;
120 u32 new_mult, new_shift;
128 WARN_ON(!irqs_disabled());
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);
133 new_mask = CLOCKSOURCE_MASK(bits);
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));
139 /* update epoch for new counter and update epoch_ns from old counter*/
141 cyc = read_sched_clock();
142 ns = cd.epoch_ns + cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
145 raw_write_seqcount_begin(&cd.seq);
146 read_sched_clock = read;
147 sched_clock_mask = new_mask;
149 cd.wrap_kt = new_wrap_kt;
151 cd.shift = new_shift;
152 cd.epoch_cyc = new_epoch;
154 raw_write_seqcount_end(&cd.seq);
160 } else if (r >= 1000) {
166 /* calculate the ns resolution of this counter */
167 res = cyc_to_ns(1ULL, new_mult, new_shift);
169 pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
170 bits, r, r_unit, res, wrap);
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();
176 pr_debug("Registered %pF as sched_clock source\n", read);
179 void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
181 read_sched_clock_32 = read;
182 sched_clock_register(read_sched_clock_32_wrapper, bits, rate);
185 void __init sched_clock_postinit(void)
188 * If no sched_clock function has been provided at that point,
189 * make it the final one one.
191 if (read_sched_clock == jiffy_sched_clock_read)
192 sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
194 update_sched_clock();
197 * Start the timer to keep sched_clock() properly updated and
198 * sets the initial epoch.
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);
205 static int sched_clock_suspend(void)
207 update_sched_clock();
208 hrtimer_cancel(&sched_clock_timer);
213 static void sched_clock_resume(void)
215 cd.epoch_cyc = read_sched_clock();
216 hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
217 cd.suspended = false;
220 static struct syscore_ops sched_clock_ops = {
221 .suspend = sched_clock_suspend,
222 .resume = sched_clock_resume,
225 static int __init sched_clock_syscore_init(void)
227 register_syscore_ops(&sched_clock_ops);
230 device_initcall(sched_clock_syscore_init);