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3e51f33f PZ |
1 | /* |
2 | * sched_clock for unstable cpu clocks | |
3 | * | |
4 | * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> | |
5 | * | |
6 | * Based on code by: | |
7 | * Ingo Molnar <mingo@redhat.com> | |
8 | * Guillaume Chazarain <guichaz@gmail.com> | |
9 | * | |
10 | * Create a semi stable clock from a mixture of other events, including: | |
11 | * - gtod | |
12 | * - jiffies | |
13 | * - sched_clock() | |
14 | * - explicit idle events | |
15 | * | |
16 | * We use gtod as base and the unstable clock deltas. The deltas are filtered, | |
17 | * making it monotonic and keeping it within an expected window. This window | |
18 | * is set up using jiffies. | |
19 | * | |
20 | * Furthermore, explicit sleep and wakeup hooks allow us to account for time | |
21 | * that is otherwise invisible (TSC gets stopped). | |
22 | * | |
23 | * The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat | |
24 | * consistent between cpus (never more than 1 jiffies difference). | |
25 | */ | |
26 | #include <linux/sched.h> | |
27 | #include <linux/percpu.h> | |
28 | #include <linux/spinlock.h> | |
29 | #include <linux/ktime.h> | |
30 | #include <linux/module.h> | |
31 | ||
32 | ||
33 | #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK | |
34 | ||
35 | struct sched_clock_data { | |
36 | /* | |
37 | * Raw spinlock - this is a special case: this might be called | |
38 | * from within instrumentation code so we dont want to do any | |
39 | * instrumentation ourselves. | |
40 | */ | |
41 | raw_spinlock_t lock; | |
42 | ||
62c43dd9 | 43 | unsigned long tick_jiffies; |
3e51f33f PZ |
44 | u64 prev_raw; |
45 | u64 tick_raw; | |
46 | u64 tick_gtod; | |
47 | u64 clock; | |
af52a90a SR |
48 | #ifdef CONFIG_NO_HZ |
49 | int check_max; | |
50 | #endif | |
3e51f33f PZ |
51 | }; |
52 | ||
53 | static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data); | |
54 | ||
55 | static inline struct sched_clock_data *this_scd(void) | |
56 | { | |
57 | return &__get_cpu_var(sched_clock_data); | |
58 | } | |
59 | ||
60 | static inline struct sched_clock_data *cpu_sdc(int cpu) | |
61 | { | |
62 | return &per_cpu(sched_clock_data, cpu); | |
63 | } | |
64 | ||
a381759d PZ |
65 | static __read_mostly int sched_clock_running; |
66 | ||
3e51f33f PZ |
67 | void sched_clock_init(void) |
68 | { | |
69 | u64 ktime_now = ktime_to_ns(ktime_get()); | |
a381759d | 70 | unsigned long now_jiffies = jiffies; |
3e51f33f PZ |
71 | int cpu; |
72 | ||
73 | for_each_possible_cpu(cpu) { | |
74 | struct sched_clock_data *scd = cpu_sdc(cpu); | |
75 | ||
76 | scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED; | |
62c43dd9 | 77 | scd->tick_jiffies = now_jiffies; |
a381759d PZ |
78 | scd->prev_raw = 0; |
79 | scd->tick_raw = 0; | |
3e51f33f PZ |
80 | scd->tick_gtod = ktime_now; |
81 | scd->clock = ktime_now; | |
af52a90a SR |
82 | #ifdef CONFIG_NO_HZ |
83 | scd->check_max = 1; | |
84 | #endif | |
3e51f33f | 85 | } |
a381759d PZ |
86 | |
87 | sched_clock_running = 1; | |
3e51f33f PZ |
88 | } |
89 | ||
af52a90a SR |
90 | #ifdef CONFIG_NO_HZ |
91 | /* | |
92 | * The dynamic ticks makes the delta jiffies inaccurate. This | |
93 | * prevents us from checking the maximum time update. | |
94 | * Disable the maximum check during stopped ticks. | |
95 | */ | |
96 | void sched_clock_tick_stop(int cpu) | |
97 | { | |
98 | struct sched_clock_data *scd = cpu_sdc(cpu); | |
99 | ||
100 | scd->check_max = 0; | |
101 | } | |
102 | ||
103 | void sched_clock_tick_start(int cpu) | |
104 | { | |
105 | struct sched_clock_data *scd = cpu_sdc(cpu); | |
106 | ||
107 | scd->check_max = 1; | |
108 | } | |
109 | ||
110 | static int check_max(struct sched_clock_data *scd) | |
111 | { | |
112 | return scd->check_max; | |
113 | } | |
114 | #else | |
115 | static int check_max(struct sched_clock_data *scd) | |
116 | { | |
117 | return 1; | |
118 | } | |
119 | #endif /* CONFIG_NO_HZ */ | |
120 | ||
3e51f33f PZ |
121 | /* |
122 | * update the percpu scd from the raw @now value | |
123 | * | |
124 | * - filter out backward motion | |
125 | * - use jiffies to generate a min,max window to clip the raw values | |
126 | */ | |
c0c87734 | 127 | static void __update_sched_clock(struct sched_clock_data *scd, u64 now, u64 *time) |
3e51f33f PZ |
128 | { |
129 | unsigned long now_jiffies = jiffies; | |
62c43dd9 | 130 | long delta_jiffies = now_jiffies - scd->tick_jiffies; |
3e51f33f PZ |
131 | u64 clock = scd->clock; |
132 | u64 min_clock, max_clock; | |
133 | s64 delta = now - scd->prev_raw; | |
134 | ||
135 | WARN_ON_ONCE(!irqs_disabled()); | |
f7cce27f SR |
136 | |
137 | min_clock = scd->tick_gtod + | |
138 | (delta_jiffies ? delta_jiffies - 1 : 0) * TICK_NSEC; | |
3e51f33f PZ |
139 | |
140 | if (unlikely(delta < 0)) { | |
141 | clock++; | |
142 | goto out; | |
143 | } | |
144 | ||
f7cce27f SR |
145 | /* |
146 | * The clock must stay within a jiffie of the gtod. | |
147 | * But since we may be at the start of a jiffy or the end of one | |
148 | * we add another jiffy buffer. | |
149 | */ | |
150 | max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC; | |
3e51f33f | 151 | |
af52a90a | 152 | if (unlikely(clock + delta > max_clock) && check_max(scd)) { |
3e51f33f PZ |
153 | if (clock < max_clock) |
154 | clock = max_clock; | |
155 | else | |
156 | clock++; | |
157 | } else { | |
158 | clock += delta; | |
159 | } | |
160 | ||
161 | out: | |
162 | if (unlikely(clock < min_clock)) | |
163 | clock = min_clock; | |
164 | ||
c0c87734 SR |
165 | if (time) |
166 | *time = clock; | |
167 | else { | |
168 | scd->prev_raw = now; | |
169 | scd->clock = clock; | |
170 | } | |
3e51f33f PZ |
171 | } |
172 | ||
173 | static void lock_double_clock(struct sched_clock_data *data1, | |
174 | struct sched_clock_data *data2) | |
175 | { | |
176 | if (data1 < data2) { | |
177 | __raw_spin_lock(&data1->lock); | |
178 | __raw_spin_lock(&data2->lock); | |
179 | } else { | |
180 | __raw_spin_lock(&data2->lock); | |
181 | __raw_spin_lock(&data1->lock); | |
182 | } | |
183 | } | |
184 | ||
185 | u64 sched_clock_cpu(int cpu) | |
186 | { | |
187 | struct sched_clock_data *scd = cpu_sdc(cpu); | |
188 | u64 now, clock; | |
189 | ||
a381759d PZ |
190 | if (unlikely(!sched_clock_running)) |
191 | return 0ull; | |
192 | ||
3e51f33f PZ |
193 | WARN_ON_ONCE(!irqs_disabled()); |
194 | now = sched_clock(); | |
195 | ||
196 | if (cpu != raw_smp_processor_id()) { | |
197 | /* | |
198 | * in order to update a remote cpu's clock based on our | |
199 | * unstable raw time rebase it against: | |
200 | * tick_raw (offset between raw counters) | |
201 | * tick_gotd (tick offset between cpus) | |
202 | */ | |
203 | struct sched_clock_data *my_scd = this_scd(); | |
204 | ||
205 | lock_double_clock(scd, my_scd); | |
206 | ||
207 | now -= my_scd->tick_raw; | |
208 | now += scd->tick_raw; | |
209 | ||
2b8a0cf4 SR |
210 | now += my_scd->tick_gtod; |
211 | now -= scd->tick_gtod; | |
3e51f33f PZ |
212 | |
213 | __raw_spin_unlock(&my_scd->lock); | |
c0c87734 SR |
214 | |
215 | __update_sched_clock(scd, now, &clock); | |
216 | ||
217 | __raw_spin_unlock(&scd->lock); | |
218 | ||
3e51f33f PZ |
219 | } else { |
220 | __raw_spin_lock(&scd->lock); | |
c0c87734 SR |
221 | __update_sched_clock(scd, now, NULL); |
222 | clock = scd->clock; | |
223 | __raw_spin_unlock(&scd->lock); | |
3e51f33f PZ |
224 | } |
225 | ||
3e51f33f PZ |
226 | return clock; |
227 | } | |
228 | ||
229 | void sched_clock_tick(void) | |
230 | { | |
231 | struct sched_clock_data *scd = this_scd(); | |
62c43dd9 | 232 | unsigned long now_jiffies = jiffies; |
3e51f33f PZ |
233 | u64 now, now_gtod; |
234 | ||
a381759d PZ |
235 | if (unlikely(!sched_clock_running)) |
236 | return; | |
237 | ||
3e51f33f PZ |
238 | WARN_ON_ONCE(!irqs_disabled()); |
239 | ||
240 | now = sched_clock(); | |
241 | now_gtod = ktime_to_ns(ktime_get()); | |
242 | ||
243 | __raw_spin_lock(&scd->lock); | |
c0c87734 | 244 | __update_sched_clock(scd, now, NULL); |
3e51f33f PZ |
245 | /* |
246 | * update tick_gtod after __update_sched_clock() because that will | |
247 | * already observe 1 new jiffy; adding a new tick_gtod to that would | |
248 | * increase the clock 2 jiffies. | |
249 | */ | |
62c43dd9 | 250 | scd->tick_jiffies = now_jiffies; |
3e51f33f PZ |
251 | scd->tick_raw = now; |
252 | scd->tick_gtod = now_gtod; | |
253 | __raw_spin_unlock(&scd->lock); | |
254 | } | |
255 | ||
256 | /* | |
257 | * We are going deep-idle (irqs are disabled): | |
258 | */ | |
259 | void sched_clock_idle_sleep_event(void) | |
260 | { | |
261 | sched_clock_cpu(smp_processor_id()); | |
262 | } | |
263 | EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event); | |
264 | ||
265 | /* | |
266 | * We just idled delta nanoseconds (called with irqs disabled): | |
267 | */ | |
268 | void sched_clock_idle_wakeup_event(u64 delta_ns) | |
269 | { | |
270 | struct sched_clock_data *scd = this_scd(); | |
271 | u64 now = sched_clock(); | |
272 | ||
273 | /* | |
274 | * Override the previous timestamp and ignore all | |
275 | * sched_clock() deltas that occured while we idled, | |
276 | * and use the PM-provided delta_ns to advance the | |
277 | * rq clock: | |
278 | */ | |
279 | __raw_spin_lock(&scd->lock); | |
280 | scd->prev_raw = now; | |
281 | scd->clock += delta_ns; | |
282 | __raw_spin_unlock(&scd->lock); | |
283 | ||
284 | touch_softlockup_watchdog(); | |
285 | } | |
286 | EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event); | |
287 | ||
288 | #endif | |
289 | ||
290 | /* | |
291 | * Scheduler clock - returns current time in nanosec units. | |
292 | * This is default implementation. | |
293 | * Architectures and sub-architectures can override this. | |
294 | */ | |
295 | unsigned long long __attribute__((weak)) sched_clock(void) | |
296 | { | |
297 | return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ); | |
298 | } |