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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Generic sched_clock() support, to extend low level hardware time
4 * counters to full 64-bit ns values.
5 */
6#include <linux/clocksource.h>
7#include <linux/init.h>
8#include <linux/jiffies.h>
9#include <linux/ktime.h>
10#include <linux/kernel.h>
11#include <linux/moduleparam.h>
12#include <linux/sched.h>
13#include <linux/sched/clock.h>
14#include <linux/syscore_ops.h>
15#include <linux/hrtimer.h>
16#include <linux/sched_clock.h>
17#include <linux/seqlock.h>
18#include <linux/bitops.h>
19
20#include "timekeeping.h"
21
22/**
23 * struct clock_read_data - data required to read from sched_clock()
24 *
25 * @epoch_ns: sched_clock() value at last update
26 * @epoch_cyc: Clock cycle value at last update.
27 * @sched_clock_mask: Bitmask for two's complement subtraction of non 64bit
28 * clocks.
29 * @read_sched_clock: Current clock source (or dummy source when suspended).
30 * @mult: Multipler for scaled math conversion.
31 * @shift: Shift value for scaled math conversion.
32 *
33 * Care must be taken when updating this structure; it is read by
34 * some very hot code paths. It occupies <=40 bytes and, when combined
35 * with the seqcount used to synchronize access, comfortably fits into
36 * a 64 byte cache line.
37 */
38struct clock_read_data {
39 u64 epoch_ns;
40 u64 epoch_cyc;
41 u64 sched_clock_mask;
42 u64 (*read_sched_clock)(void);
43 u32 mult;
44 u32 shift;
45};
46
47/**
48 * struct clock_data - all data needed for sched_clock() (including
49 * registration of a new clock source)
50 *
51 * @seq: Sequence counter for protecting updates. The lowest
52 * bit is the index for @read_data.
53 * @read_data: Data required to read from sched_clock.
54 * @wrap_kt: Duration for which clock can run before wrapping.
55 * @rate: Tick rate of the registered clock.
56 * @actual_read_sched_clock: Registered hardware level clock read function.
57 *
58 * The ordering of this structure has been chosen to optimize cache
59 * performance. In particular 'seq' and 'read_data[0]' (combined) should fit
60 * into a single 64-byte cache line.
61 */
62struct clock_data {
63 seqcount_t seq;
64 struct clock_read_data read_data[2];
65 ktime_t wrap_kt;
66 unsigned long rate;
67
68 u64 (*actual_read_sched_clock)(void);
69};
70
71static struct hrtimer sched_clock_timer;
72static int irqtime = -1;
73
74core_param(irqtime, irqtime, int, 0400);
75
76static u64 notrace jiffy_sched_clock_read(void)
77{
78 /*
79 * We don't need to use get_jiffies_64 on 32-bit arches here
80 * because we register with BITS_PER_LONG
81 */
82 return (u64)(jiffies - INITIAL_JIFFIES);
83}
84
85static struct clock_data cd ____cacheline_aligned = {
86 .read_data[0] = { .mult = NSEC_PER_SEC / HZ,
87 .read_sched_clock = jiffy_sched_clock_read, },
88 .actual_read_sched_clock = jiffy_sched_clock_read,
89};
90
91static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
92{
93 return (cyc * mult) >> shift;
94}
95
96unsigned long long notrace sched_clock(void)
97{
98 u64 cyc, res;
99 unsigned int seq;
100 struct clock_read_data *rd;
101
102 do {
103 seq = raw_read_seqcount(&cd.seq);
104 rd = cd.read_data + (seq & 1);
105
106 cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
107 rd->sched_clock_mask;
108 res = rd->epoch_ns + cyc_to_ns(cyc, rd->mult, rd->shift);
109 } while (read_seqcount_retry(&cd.seq, seq));
110
111 return res;
112}
113
114/*
115 * Updating the data required to read the clock.
116 *
117 * sched_clock() will never observe mis-matched data even if called from
118 * an NMI. We do this by maintaining an odd/even copy of the data and
119 * steering sched_clock() to one or the other using a sequence counter.
120 * In order to preserve the data cache profile of sched_clock() as much
121 * as possible the system reverts back to the even copy when the update
122 * completes; the odd copy is used *only* during an update.
123 */
124static void update_clock_read_data(struct clock_read_data *rd)
125{
126 /* update the backup (odd) copy with the new data */
127 cd.read_data[1] = *rd;
128
129 /* steer readers towards the odd copy */
130 raw_write_seqcount_latch(&cd.seq);
131
132 /* now its safe for us to update the normal (even) copy */
133 cd.read_data[0] = *rd;
134
135 /* switch readers back to the even copy */
136 raw_write_seqcount_latch(&cd.seq);
137}
138
139/*
140 * Atomically update the sched_clock() epoch.
141 */
142static void update_sched_clock(void)
143{
144 u64 cyc;
145 u64 ns;
146 struct clock_read_data rd;
147
148 rd = cd.read_data[0];
149
150 cyc = cd.actual_read_sched_clock();
151 ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
152
153 rd.epoch_ns = ns;
154 rd.epoch_cyc = cyc;
155
156 update_clock_read_data(&rd);
157}
158
159static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
160{
161 update_sched_clock();
162 hrtimer_forward_now(hrt, cd.wrap_kt);
163
164 return HRTIMER_RESTART;
165}
166
167void __init
168sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)
169{
170 u64 res, wrap, new_mask, new_epoch, cyc, ns;
171 u32 new_mult, new_shift;
172 unsigned long r;
173 char r_unit;
174 struct clock_read_data rd;
175
176 if (cd.rate > rate)
177 return;
178
179 WARN_ON(!irqs_disabled());
180
181 /* Calculate the mult/shift to convert counter ticks to ns. */
182 clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
183
184 new_mask = CLOCKSOURCE_MASK(bits);
185 cd.rate = rate;
186
187 /* Calculate how many nanosecs until we risk wrapping */
188 wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);
189 cd.wrap_kt = ns_to_ktime(wrap);
190
191 rd = cd.read_data[0];
192
193 /* Update epoch for new counter and update 'epoch_ns' from old counter*/
194 new_epoch = read();
195 cyc = cd.actual_read_sched_clock();
196 ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
197 cd.actual_read_sched_clock = read;
198
199 rd.read_sched_clock = read;
200 rd.sched_clock_mask = new_mask;
201 rd.mult = new_mult;
202 rd.shift = new_shift;
203 rd.epoch_cyc = new_epoch;
204 rd.epoch_ns = ns;
205
206 update_clock_read_data(&rd);
207
208 if (sched_clock_timer.function != NULL) {
209 /* update timeout for clock wrap */
210 hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
211 }
212
213 r = rate;
214 if (r >= 4000000) {
215 r /= 1000000;
216 r_unit = 'M';
217 } else {
218 if (r >= 1000) {
219 r /= 1000;
220 r_unit = 'k';
221 } else {
222 r_unit = ' ';
223 }
224 }
225
226 /* Calculate the ns resolution of this counter */
227 res = cyc_to_ns(1ULL, new_mult, new_shift);
228
229 pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
230 bits, r, r_unit, res, wrap);
231
232 /* Enable IRQ time accounting if we have a fast enough sched_clock() */
233 if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
234 enable_sched_clock_irqtime();
235
236 pr_debug("Registered %pS as sched_clock source\n", read);
237}
238
239void __init generic_sched_clock_init(void)
240{
241 /*
242 * If no sched_clock() function has been provided at that point,
243 * make it the final one one.
244 */
245 if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
246 sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
247
248 update_sched_clock();
249
250 /*
251 * Start the timer to keep sched_clock() properly updated and
252 * sets the initial epoch.
253 */
254 hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
255 sched_clock_timer.function = sched_clock_poll;
256 hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
257}
258
259/*
260 * Clock read function for use when the clock is suspended.
261 *
262 * This function makes it appear to sched_clock() as if the clock
263 * stopped counting at its last update.
264 *
265 * This function must only be called from the critical
266 * section in sched_clock(). It relies on the read_seqcount_retry()
267 * at the end of the critical section to be sure we observe the
268 * correct copy of 'epoch_cyc'.
269 */
270static u64 notrace suspended_sched_clock_read(void)
271{
272 unsigned int seq = raw_read_seqcount(&cd.seq);
273
274 return cd.read_data[seq & 1].epoch_cyc;
275}
276
277int sched_clock_suspend(void)
278{
279 struct clock_read_data *rd = &cd.read_data[0];
280
281 update_sched_clock();
282 hrtimer_cancel(&sched_clock_timer);
283 rd->read_sched_clock = suspended_sched_clock_read;
284
285 return 0;
286}
287
288void sched_clock_resume(void)
289{
290 struct clock_read_data *rd = &cd.read_data[0];
291
292 rd->epoch_cyc = cd.actual_read_sched_clock();
293 hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
294 rd->read_sched_clock = cd.actual_read_sched_clock;
295}
296
297static struct syscore_ops sched_clock_ops = {
298 .suspend = sched_clock_suspend,
299 .resume = sched_clock_resume,
300};
301
302static int __init sched_clock_syscore_init(void)
303{
304 register_syscore_ops(&sched_clock_ops);
305
306 return 0;
307}
308device_initcall(sched_clock_syscore_init);
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Generic sched_clock() support, to extend low level hardware time
4 * counters to full 64-bit ns values.
5 */
6#include <linux/clocksource.h>
7#include <linux/init.h>
8#include <linux/jiffies.h>
9#include <linux/ktime.h>
10#include <linux/kernel.h>
11#include <linux/math.h>
12#include <linux/moduleparam.h>
13#include <linux/sched.h>
14#include <linux/sched/clock.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
21#include "timekeeping.h"
22
23/**
24 * struct clock_data - all data needed for sched_clock() (including
25 * registration of a new clock source)
26 *
27 * @seq: Sequence counter for protecting updates. The lowest
28 * bit is the index for @read_data.
29 * @read_data: Data required to read from sched_clock.
30 * @wrap_kt: Duration for which clock can run before wrapping.
31 * @rate: Tick rate of the registered clock.
32 * @actual_read_sched_clock: Registered hardware level clock read function.
33 *
34 * The ordering of this structure has been chosen to optimize cache
35 * performance. In particular 'seq' and 'read_data[0]' (combined) should fit
36 * into a single 64-byte cache line.
37 */
38struct clock_data {
39 seqcount_latch_t seq;
40 struct clock_read_data read_data[2];
41 ktime_t wrap_kt;
42 unsigned long rate;
43
44 u64 (*actual_read_sched_clock)(void);
45};
46
47static struct hrtimer sched_clock_timer;
48static int irqtime = -1;
49
50core_param(irqtime, irqtime, int, 0400);
51
52static u64 notrace jiffy_sched_clock_read(void)
53{
54 /*
55 * We don't need to use get_jiffies_64 on 32-bit arches here
56 * because we register with BITS_PER_LONG
57 */
58 return (u64)(jiffies - INITIAL_JIFFIES);
59}
60
61static struct clock_data cd ____cacheline_aligned = {
62 .read_data[0] = { .mult = NSEC_PER_SEC / HZ,
63 .read_sched_clock = jiffy_sched_clock_read, },
64 .actual_read_sched_clock = jiffy_sched_clock_read,
65};
66
67static __always_inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
68{
69 return (cyc * mult) >> shift;
70}
71
72notrace struct clock_read_data *sched_clock_read_begin(unsigned int *seq)
73{
74 *seq = read_seqcount_latch(&cd.seq);
75 return cd.read_data + (*seq & 1);
76}
77
78notrace int sched_clock_read_retry(unsigned int seq)
79{
80 return read_seqcount_latch_retry(&cd.seq, seq);
81}
82
83static __always_inline unsigned long long __sched_clock(void)
84{
85 struct clock_read_data *rd;
86 unsigned int seq;
87 u64 cyc, res;
88
89 do {
90 seq = raw_read_seqcount_latch(&cd.seq);
91 rd = cd.read_data + (seq & 1);
92
93 cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
94 rd->sched_clock_mask;
95 res = rd->epoch_ns + cyc_to_ns(cyc, rd->mult, rd->shift);
96 } while (raw_read_seqcount_latch_retry(&cd.seq, seq));
97
98 return res;
99}
100
101unsigned long long noinstr sched_clock_noinstr(void)
102{
103 return __sched_clock();
104}
105
106unsigned long long notrace sched_clock(void)
107{
108 unsigned long long ns;
109 preempt_disable_notrace();
110 /*
111 * All of __sched_clock() is a seqcount_latch reader critical section,
112 * but relies on the raw helpers which are uninstrumented. For KCSAN,
113 * mark all accesses in __sched_clock() as atomic.
114 */
115 kcsan_nestable_atomic_begin();
116 ns = __sched_clock();
117 kcsan_nestable_atomic_end();
118 preempt_enable_notrace();
119 return ns;
120}
121
122/*
123 * Updating the data required to read the clock.
124 *
125 * sched_clock() will never observe mis-matched data even if called from
126 * an NMI. We do this by maintaining an odd/even copy of the data and
127 * steering sched_clock() to one or the other using a sequence counter.
128 * In order to preserve the data cache profile of sched_clock() as much
129 * as possible the system reverts back to the even copy when the update
130 * completes; the odd copy is used *only* during an update.
131 */
132static void update_clock_read_data(struct clock_read_data *rd)
133{
134 /* steer readers towards the odd copy */
135 write_seqcount_latch_begin(&cd.seq);
136
137 /* now its safe for us to update the normal (even) copy */
138 cd.read_data[0] = *rd;
139
140 /* switch readers back to the even copy */
141 write_seqcount_latch(&cd.seq);
142
143 /* update the backup (odd) copy with the new data */
144 cd.read_data[1] = *rd;
145
146 write_seqcount_latch_end(&cd.seq);
147}
148
149/*
150 * Atomically update the sched_clock() epoch.
151 */
152static void update_sched_clock(void)
153{
154 u64 cyc;
155 u64 ns;
156 struct clock_read_data rd;
157
158 rd = cd.read_data[0];
159
160 cyc = cd.actual_read_sched_clock();
161 ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
162
163 rd.epoch_ns = ns;
164 rd.epoch_cyc = cyc;
165
166 update_clock_read_data(&rd);
167}
168
169static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
170{
171 update_sched_clock();
172 hrtimer_forward_now(hrt, cd.wrap_kt);
173
174 return HRTIMER_RESTART;
175}
176
177void __init
178sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)
179{
180 u64 res, wrap, new_mask, new_epoch, cyc, ns;
181 u32 new_mult, new_shift;
182 unsigned long r, flags;
183 char r_unit;
184 struct clock_read_data rd;
185
186 if (cd.rate > rate)
187 return;
188
189 /* Cannot register a sched_clock with interrupts on */
190 local_irq_save(flags);
191
192 /* Calculate the mult/shift to convert counter ticks to ns. */
193 clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
194
195 new_mask = CLOCKSOURCE_MASK(bits);
196 cd.rate = rate;
197
198 /* Calculate how many nanosecs until we risk wrapping */
199 wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);
200 cd.wrap_kt = ns_to_ktime(wrap);
201
202 rd = cd.read_data[0];
203
204 /* Update epoch for new counter and update 'epoch_ns' from old counter*/
205 new_epoch = read();
206 cyc = cd.actual_read_sched_clock();
207 ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
208 cd.actual_read_sched_clock = read;
209
210 rd.read_sched_clock = read;
211 rd.sched_clock_mask = new_mask;
212 rd.mult = new_mult;
213 rd.shift = new_shift;
214 rd.epoch_cyc = new_epoch;
215 rd.epoch_ns = ns;
216
217 update_clock_read_data(&rd);
218
219 if (sched_clock_timer.function != NULL) {
220 /* update timeout for clock wrap */
221 hrtimer_start(&sched_clock_timer, cd.wrap_kt,
222 HRTIMER_MODE_REL_HARD);
223 }
224
225 r = rate;
226 if (r >= 4000000) {
227 r = DIV_ROUND_CLOSEST(r, 1000000);
228 r_unit = 'M';
229 } else if (r >= 4000) {
230 r = DIV_ROUND_CLOSEST(r, 1000);
231 r_unit = 'k';
232 } else {
233 r_unit = ' ';
234 }
235
236 /* Calculate the ns resolution of this counter */
237 res = cyc_to_ns(1ULL, new_mult, new_shift);
238
239 pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
240 bits, r, r_unit, res, wrap);
241
242 /* Enable IRQ time accounting if we have a fast enough sched_clock() */
243 if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
244 enable_sched_clock_irqtime();
245
246 local_irq_restore(flags);
247
248 pr_debug("Registered %pS as sched_clock source\n", read);
249}
250
251void __init generic_sched_clock_init(void)
252{
253 /*
254 * If no sched_clock() function has been provided at that point,
255 * make it the final one.
256 */
257 if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
258 sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
259
260 update_sched_clock();
261
262 /*
263 * Start the timer to keep sched_clock() properly updated and
264 * sets the initial epoch.
265 */
266 hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
267 sched_clock_timer.function = sched_clock_poll;
268 hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL_HARD);
269}
270
271/*
272 * Clock read function for use when the clock is suspended.
273 *
274 * This function makes it appear to sched_clock() as if the clock
275 * stopped counting at its last update.
276 *
277 * This function must only be called from the critical
278 * section in sched_clock(). It relies on the read_seqcount_retry()
279 * at the end of the critical section to be sure we observe the
280 * correct copy of 'epoch_cyc'.
281 */
282static u64 notrace suspended_sched_clock_read(void)
283{
284 unsigned int seq = read_seqcount_latch(&cd.seq);
285
286 return cd.read_data[seq & 1].epoch_cyc;
287}
288
289int sched_clock_suspend(void)
290{
291 struct clock_read_data *rd = &cd.read_data[0];
292
293 update_sched_clock();
294 hrtimer_cancel(&sched_clock_timer);
295 rd->read_sched_clock = suspended_sched_clock_read;
296
297 return 0;
298}
299
300void sched_clock_resume(void)
301{
302 struct clock_read_data *rd = &cd.read_data[0];
303
304 rd->epoch_cyc = cd.actual_read_sched_clock();
305 hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL_HARD);
306 rd->read_sched_clock = cd.actual_read_sched_clock;
307}
308
309static struct syscore_ops sched_clock_ops = {
310 .suspend = sched_clock_suspend,
311 .resume = sched_clock_resume,
312};
313
314static int __init sched_clock_syscore_init(void)
315{
316 register_syscore_ops(&sched_clock_ops);
317
318 return 0;
319}
320device_initcall(sched_clock_syscore_init);