2 * sched_clock for unstable cpu clocks
4 * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
6 * Updates and enhancements:
7 * Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
10 * Ingo Molnar <mingo@redhat.com>
11 * Guillaume Chazarain <guichaz@gmail.com>
13 * Create a semi stable clock from a mixture of other events, including:
17 * - explicit idle events
19 * We use gtod as base and the unstable clock deltas. The deltas are filtered,
20 * making it monotonic and keeping it within an expected window. This window
21 * is set up using jiffies.
23 * Furthermore, explicit sleep and wakeup hooks allow us to account for time
24 * that is otherwise invisible (TSC gets stopped).
26 * The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
27 * consistent between cpus (never more than 1 jiffies difference).
29 #include <linux/sched.h>
30 #include <linux/percpu.h>
31 #include <linux/spinlock.h>
32 #include <linux/ktime.h>
33 #include <linux/module.h>
36 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
38 #define MULTI_SHIFT 15
39 /* Max is double, Min is 1/2 */
40 #define MAX_MULTI (2LL << MULTI_SHIFT)
41 #define MIN_MULTI (1LL << (MULTI_SHIFT-1))
43 struct sched_clock_data {
45 * Raw spinlock - this is a special case: this might be called
46 * from within instrumentation code so we dont want to do any
47 * instrumentation ourselves.
51 unsigned long tick_jiffies;
62 static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
64 static inline struct sched_clock_data *this_scd(void)
66 return &__get_cpu_var(sched_clock_data);
69 static inline struct sched_clock_data *cpu_sdc(int cpu)
71 return &per_cpu(sched_clock_data, cpu);
74 static __read_mostly int sched_clock_running;
76 void sched_clock_init(void)
78 u64 ktime_now = ktime_to_ns(ktime_get());
79 unsigned long now_jiffies = jiffies;
82 for_each_possible_cpu(cpu) {
83 struct sched_clock_data *scd = cpu_sdc(cpu);
85 scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
86 scd->tick_jiffies = now_jiffies;
89 scd->tick_gtod = ktime_now;
90 scd->clock = ktime_now;
91 scd->multi = 1 << MULTI_SHIFT;
97 sched_clock_running = 1;
102 * The dynamic ticks makes the delta jiffies inaccurate. This
103 * prevents us from checking the maximum time update.
104 * Disable the maximum check during stopped ticks.
106 void sched_clock_tick_stop(int cpu)
108 struct sched_clock_data *scd = cpu_sdc(cpu);
113 void sched_clock_tick_start(int cpu)
115 struct sched_clock_data *scd = cpu_sdc(cpu);
120 static int check_max(struct sched_clock_data *scd)
122 return scd->check_max;
125 static int check_max(struct sched_clock_data *scd)
129 #endif /* CONFIG_NO_HZ */
132 * update the percpu scd from the raw @now value
134 * - filter out backward motion
135 * - use jiffies to generate a min,max window to clip the raw values
137 static void __update_sched_clock(struct sched_clock_data *scd, u64 now, u64 *time)
139 unsigned long now_jiffies = jiffies;
140 long delta_jiffies = now_jiffies - scd->tick_jiffies;
141 u64 clock = scd->clock;
142 u64 min_clock, max_clock;
143 s64 delta = now - scd->prev_raw;
145 WARN_ON_ONCE(!irqs_disabled());
148 * At schedule tick the clock can be just under the gtod. We don't
149 * want to push it too prematurely.
151 min_clock = scd->tick_gtod + (delta_jiffies * TICK_NSEC);
152 if (min_clock > TICK_NSEC)
153 min_clock -= TICK_NSEC / 2;
155 if (unlikely(delta < 0)) {
161 * The clock must stay within a jiffie of the gtod.
162 * But since we may be at the start of a jiffy or the end of one
163 * we add another jiffy buffer.
165 max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC;
168 delta >>= MULTI_SHIFT;
170 if (unlikely(clock + delta > max_clock) && check_max(scd)) {
171 if (clock < max_clock)
180 if (unlikely(clock < min_clock))
191 static void lock_double_clock(struct sched_clock_data *data1,
192 struct sched_clock_data *data2)
195 __raw_spin_lock(&data1->lock);
196 __raw_spin_lock(&data2->lock);
198 __raw_spin_lock(&data2->lock);
199 __raw_spin_lock(&data1->lock);
203 u64 sched_clock_cpu(int cpu)
205 struct sched_clock_data *scd = cpu_sdc(cpu);
208 if (unlikely(!sched_clock_running))
211 WARN_ON_ONCE(!irqs_disabled());
214 if (cpu != raw_smp_processor_id()) {
216 * in order to update a remote cpu's clock based on our
217 * unstable raw time rebase it against:
218 * tick_raw (offset between raw counters)
219 * tick_gotd (tick offset between cpus)
221 struct sched_clock_data *my_scd = this_scd();
223 lock_double_clock(scd, my_scd);
225 now -= my_scd->tick_raw;
226 now += scd->tick_raw;
228 now += my_scd->tick_gtod;
229 now -= scd->tick_gtod;
231 __raw_spin_unlock(&my_scd->lock);
233 __update_sched_clock(scd, now, &clock);
235 __raw_spin_unlock(&scd->lock);
238 __raw_spin_lock(&scd->lock);
239 __update_sched_clock(scd, now, NULL);
241 __raw_spin_unlock(&scd->lock);
247 void sched_clock_tick(void)
249 struct sched_clock_data *scd = this_scd();
250 unsigned long now_jiffies = jiffies;
251 s64 mult, delta_gtod, delta_raw;
254 if (unlikely(!sched_clock_running))
257 WARN_ON_ONCE(!irqs_disabled());
259 now_gtod = ktime_to_ns(ktime_get());
262 __raw_spin_lock(&scd->lock);
263 __update_sched_clock(scd, now, NULL);
265 * update tick_gtod after __update_sched_clock() because that will
266 * already observe 1 new jiffy; adding a new tick_gtod to that would
267 * increase the clock 2 jiffies.
269 delta_gtod = now_gtod - scd->tick_gtod;
270 delta_raw = now - scd->tick_raw;
272 if ((long)delta_raw > 0) {
273 mult = delta_gtod << MULTI_SHIFT;
274 do_div(mult, delta_raw);
276 if (scd->multi > MAX_MULTI)
277 scd->multi = MAX_MULTI;
278 else if (scd->multi < MIN_MULTI)
279 scd->multi = MIN_MULTI;
281 scd->multi = 1 << MULTI_SHIFT;
284 scd->tick_gtod = now_gtod;
285 scd->tick_jiffies = now_jiffies;
286 __raw_spin_unlock(&scd->lock);
290 * We are going deep-idle (irqs are disabled):
292 void sched_clock_idle_sleep_event(void)
294 sched_clock_cpu(smp_processor_id());
296 EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
299 * We just idled delta nanoseconds (called with irqs disabled):
301 void sched_clock_idle_wakeup_event(u64 delta_ns)
303 struct sched_clock_data *scd = this_scd();
304 u64 now = sched_clock();
307 * Override the previous timestamp and ignore all
308 * sched_clock() deltas that occured while we idled,
309 * and use the PM-provided delta_ns to advance the
312 __raw_spin_lock(&scd->lock);
314 scd->clock += delta_ns;
315 scd->multi = 1 << MULTI_SHIFT;
316 __raw_spin_unlock(&scd->lock);
318 touch_softlockup_watchdog();
320 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
325 * Scheduler clock - returns current time in nanosec units.
326 * This is default implementation.
327 * Architectures and sub-architectures can override this.
329 unsigned long long __attribute__((weak)) sched_clock(void)
331 return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
334 unsigned long long cpu_clock(int cpu)
336 unsigned long long clock;
339 local_irq_save(flags);
340 clock = sched_clock_cpu(cpu);
341 local_irq_restore(flags);
345 EXPORT_SYMBOL_GPL(cpu_clock);