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/kernel.h>
12 #include <linux/sched.h>
13 #include <linux/syscore_ops.h>
14 #include <linux/timer.h>
15
16 #include <asm/sched_clock.h>
17
18 struct clock_data {
19 u64 epoch_ns;
20 u32 epoch_cyc;
21 u32 epoch_cyc_copy;
22 u32 mult;
23 u32 shift;
24 bool suspended;
25 bool needs_suspend;
26 };
27
28 static void sched_clock_poll(unsigned long wrap_ticks);
29 static DEFINE_TIMER(sched_clock_timer, sched_clock_poll, 0, 0);
30
31 static struct clock_data cd = {
32 .mult = NSEC_PER_SEC / HZ,
33 };
34
35 static u32 __read_mostly sched_clock_mask = 0xffffffff;
36
jiffy_sched_clock_read(void)37 static u32 notrace jiffy_sched_clock_read(void)
38 {
39 return (u32)(jiffies - INITIAL_JIFFIES);
40 }
41
42 static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
43
cyc_to_ns(u64 cyc,u32 mult,u32 shift)44 static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
45 {
46 return (cyc * mult) >> shift;
47 }
48
cyc_to_sched_clock(u32 cyc,u32 mask)49 static unsigned long long cyc_to_sched_clock(u32 cyc, u32 mask)
50 {
51 u64 epoch_ns;
52 u32 epoch_cyc;
53
54 if (cd.suspended)
55 return cd.epoch_ns;
56
57 /*
58 * Load the epoch_cyc and epoch_ns atomically. We do this by
59 * ensuring that we always write epoch_cyc, epoch_ns and
60 * epoch_cyc_copy in strict order, and read them in strict order.
61 * If epoch_cyc and epoch_cyc_copy are not equal, then we're in
62 * the middle of an update, and we should repeat the load.
63 */
64 do {
65 epoch_cyc = cd.epoch_cyc;
66 smp_rmb();
67 epoch_ns = cd.epoch_ns;
68 smp_rmb();
69 } while (epoch_cyc != cd.epoch_cyc_copy);
70
71 return epoch_ns + cyc_to_ns((cyc - epoch_cyc) & mask, cd.mult, cd.shift);
72 }
73
74 /*
75 * Atomically update the sched_clock epoch.
76 */
update_sched_clock(void)77 static void notrace update_sched_clock(void)
78 {
79 unsigned long flags;
80 u32 cyc;
81 u64 ns;
82
83 cyc = read_sched_clock();
84 ns = cd.epoch_ns +
85 cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
86 cd.mult, cd.shift);
87 /*
88 * Write epoch_cyc and epoch_ns in a way that the update is
89 * detectable in cyc_to_fixed_sched_clock().
90 */
91 raw_local_irq_save(flags);
92 cd.epoch_cyc_copy = cyc;
93 smp_wmb();
94 cd.epoch_ns = ns;
95 smp_wmb();
96 cd.epoch_cyc = cyc;
97 raw_local_irq_restore(flags);
98 }
99
sched_clock_poll(unsigned long wrap_ticks)100 static void sched_clock_poll(unsigned long wrap_ticks)
101 {
102 mod_timer(&sched_clock_timer, round_jiffies(jiffies + wrap_ticks));
103 update_sched_clock();
104 }
105
setup_sched_clock_needs_suspend(u32 (* read)(void),int bits,unsigned long rate)106 void __init setup_sched_clock_needs_suspend(u32 (*read)(void), int bits,
107 unsigned long rate)
108 {
109 setup_sched_clock(read, bits, rate);
110 cd.needs_suspend = true;
111 }
112
setup_sched_clock(u32 (* read)(void),int bits,unsigned long rate)113 void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
114 {
115 unsigned long r, w;
116 u64 res, wrap;
117 char r_unit;
118
119 BUG_ON(bits > 32);
120 WARN_ON(!irqs_disabled());
121 WARN_ON(read_sched_clock != jiffy_sched_clock_read);
122 read_sched_clock = read;
123 sched_clock_mask = (1 << bits) - 1;
124
125 /* calculate the mult/shift to convert counter ticks to ns. */
126 clocks_calc_mult_shift(&cd.mult, &cd.shift, rate, NSEC_PER_SEC, 0);
127
128 r = rate;
129 if (r >= 4000000) {
130 r /= 1000000;
131 r_unit = 'M';
132 } else if (r >= 1000) {
133 r /= 1000;
134 r_unit = 'k';
135 } else
136 r_unit = ' ';
137
138 /* calculate how many ns until we wrap */
139 wrap = cyc_to_ns((1ULL << bits) - 1, cd.mult, cd.shift);
140 do_div(wrap, NSEC_PER_MSEC);
141 w = wrap;
142
143 /* calculate the ns resolution of this counter */
144 res = cyc_to_ns(1ULL, cd.mult, cd.shift);
145 pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lums\n",
146 bits, r, r_unit, res, w);
147
148 /*
149 * Start the timer to keep sched_clock() properly updated and
150 * sets the initial epoch.
151 */
152 sched_clock_timer.data = msecs_to_jiffies(w - (w / 10));
153 update_sched_clock();
154
155 /*
156 * Ensure that sched_clock() starts off at 0ns
157 */
158 cd.epoch_ns = 0;
159
160 pr_debug("Registered %pF as sched_clock source\n", read);
161 }
162
sched_clock(void)163 unsigned long long notrace sched_clock(void)
164 {
165 u32 cyc = read_sched_clock();
166 return cyc_to_sched_clock(cyc, sched_clock_mask);
167 }
168
sched_clock_postinit(void)169 void __init sched_clock_postinit(void)
170 {
171 /*
172 * If no sched_clock function has been provided at that point,
173 * make it the final one one.
174 */
175 if (read_sched_clock == jiffy_sched_clock_read)
176 setup_sched_clock(jiffy_sched_clock_read, 32, HZ);
177
178 sched_clock_poll(sched_clock_timer.data);
179 }
180
sched_clock_suspend(void)181 static int sched_clock_suspend(void)
182 {
183 sched_clock_poll(sched_clock_timer.data);
184 if (cd.needs_suspend)
185 cd.suspended = true;
186 return 0;
187 }
188
sched_clock_resume(void)189 static void sched_clock_resume(void)
190 {
191 if (cd.needs_suspend) {
192 cd.epoch_cyc = read_sched_clock();
193 cd.epoch_cyc_copy = cd.epoch_cyc;
194 cd.suspended = false;
195 }
196 }
197
198 static struct syscore_ops sched_clock_ops = {
199 .suspend = sched_clock_suspend,
200 .resume = sched_clock_resume,
201 };
202
sched_clock_syscore_init(void)203 static int __init sched_clock_syscore_init(void)
204 {
205 register_syscore_ops(&sched_clock_ops);
206 return 0;
207 }
208 device_initcall(sched_clock_syscore_init);
209