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/kernel.h>
12 #include <linux/moduleparam.h>
13 #include <linux/sched.h>
14 #include <linux/syscore_ops.h>
15 #include <linux/timer.h>
17 #include <asm/sched_clock.h>
29 static void sched_clock_poll(unsigned long wrap_ticks);
30 static DEFINE_TIMER(sched_clock_timer, sched_clock_poll, 0, 0);
31 static int irqtime = -1;
33 core_param(irqtime, irqtime, int, 0400);
35 static struct clock_data cd = {
36 .mult = NSEC_PER_SEC / HZ,
39 static u32 __read_mostly sched_clock_mask = 0xffffffff;
41 static u32 notrace jiffy_sched_clock_read(void)
43 return (u32)(jiffies - INITIAL_JIFFIES);
46 static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
48 static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
50 return (cyc * mult) >> shift;
53 static unsigned long long cyc_to_sched_clock(u32 cyc, u32 mask)
62 * Load the epoch_cyc and epoch_ns atomically. We do this by
63 * ensuring that we always write epoch_cyc, epoch_ns and
64 * epoch_cyc_copy in strict order, and read them in strict order.
65 * If epoch_cyc and epoch_cyc_copy are not equal, then we're in
66 * the middle of an update, and we should repeat the load.
69 epoch_cyc = cd.epoch_cyc;
71 epoch_ns = cd.epoch_ns;
73 } while (epoch_cyc != cd.epoch_cyc_copy);
75 return epoch_ns + cyc_to_ns((cyc - epoch_cyc) & mask, cd.mult, cd.shift);
79 * Atomically update the sched_clock epoch.
81 static void notrace update_sched_clock(void)
87 cyc = read_sched_clock();
89 cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
92 * Write epoch_cyc and epoch_ns in a way that the update is
93 * detectable in cyc_to_fixed_sched_clock().
95 raw_local_irq_save(flags);
96 cd.epoch_cyc_copy = cyc;
101 raw_local_irq_restore(flags);
104 static void sched_clock_poll(unsigned long wrap_ticks)
106 mod_timer(&sched_clock_timer, round_jiffies(jiffies + wrap_ticks));
107 update_sched_clock();
110 void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
117 WARN_ON(!irqs_disabled());
118 WARN_ON(read_sched_clock != jiffy_sched_clock_read);
119 read_sched_clock = read;
120 sched_clock_mask = (1 << bits) - 1;
122 /* calculate the mult/shift to convert counter ticks to ns. */
123 clocks_calc_mult_shift(&cd.mult, &cd.shift, rate, NSEC_PER_SEC, 0);
129 } else if (r >= 1000) {
135 /* calculate how many ns until we wrap */
136 wrap = cyc_to_ns((1ULL << bits) - 1, cd.mult, cd.shift);
137 do_div(wrap, NSEC_PER_MSEC);
140 /* calculate the ns resolution of this counter */
141 res = cyc_to_ns(1ULL, cd.mult, cd.shift);
142 pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lums\n",
143 bits, r, r_unit, res, w);
146 * Start the timer to keep sched_clock() properly updated and
147 * sets the initial epoch.
149 sched_clock_timer.data = msecs_to_jiffies(w - (w / 10));
150 update_sched_clock();
153 * Ensure that sched_clock() starts off at 0ns
157 /* Enable IRQ time accounting if we have a fast enough sched_clock */
158 if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
159 enable_sched_clock_irqtime();
161 pr_debug("Registered %pF as sched_clock source\n", read);
164 unsigned long long notrace sched_clock(void)
166 u32 cyc = read_sched_clock();
167 return cyc_to_sched_clock(cyc, sched_clock_mask);
170 void __init sched_clock_postinit(void)
173 * If no sched_clock function has been provided at that point,
174 * make it the final one one.
176 if (read_sched_clock == jiffy_sched_clock_read)
177 setup_sched_clock(jiffy_sched_clock_read, 32, HZ);
179 sched_clock_poll(sched_clock_timer.data);
182 static int sched_clock_suspend(void)
184 sched_clock_poll(sched_clock_timer.data);
189 static void sched_clock_resume(void)
191 cd.epoch_cyc = read_sched_clock();
192 cd.epoch_cyc_copy = cd.epoch_cyc;
193 cd.suspended = false;
196 static struct syscore_ops sched_clock_ops = {
197 .suspend = sched_clock_suspend,
198 .resume = sched_clock_resume,
201 static int __init sched_clock_syscore_init(void)
203 register_syscore_ops(&sched_clock_ops);
206 device_initcall(sched_clock_syscore_init);