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 * Scheduler clock - returns current time in nanosec units.
37 * This is default implementation.
38 * Architectures and sub-architectures can override this.
40 unsigned long long __attribute__((weak)) sched_clock(void)
42 return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
45 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
47 struct sched_clock_data {
49 * Raw spinlock - this is a special case: this might be called
50 * from within instrumentation code so we dont want to do any
51 * instrumentation ourselves.
55 unsigned long tick_jiffies;
61 static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
63 static inline struct sched_clock_data *this_scd(void)
65 return &__get_cpu_var(sched_clock_data);
68 static inline struct sched_clock_data *cpu_sdc(int cpu)
70 return &per_cpu(sched_clock_data, cpu);
73 static __read_mostly int sched_clock_running;
75 void sched_clock_init(void)
77 u64 ktime_now = ktime_to_ns(ktime_get());
78 unsigned long now_jiffies = jiffies;
81 for_each_possible_cpu(cpu) {
82 struct sched_clock_data *scd = cpu_sdc(cpu);
84 scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
85 scd->tick_jiffies = now_jiffies;
87 scd->tick_gtod = ktime_now;
88 scd->clock = ktime_now;
91 sched_clock_running = 1;
95 * update the percpu scd from the raw @now value
97 * - filter out backward motion
98 * - use jiffies to generate a min,max window to clip the raw values
100 static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
102 unsigned long now_jiffies = jiffies;
103 long delta_jiffies = now_jiffies - scd->tick_jiffies;
104 u64 clock = scd->clock;
105 u64 min_clock, max_clock;
106 s64 delta = now - scd->tick_raw;
108 WARN_ON_ONCE(!irqs_disabled());
109 min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC;
111 if (unlikely(delta < 0)) {
116 max_clock = min_clock + TICK_NSEC;
118 if (unlikely(clock + delta > max_clock)) {
119 if (clock < max_clock)
128 if (unlikely(clock < min_clock))
131 scd->tick_jiffies = now_jiffies;
137 static void lock_double_clock(struct sched_clock_data *data1,
138 struct sched_clock_data *data2)
141 __raw_spin_lock(&data1->lock);
142 __raw_spin_lock(&data2->lock);
144 __raw_spin_lock(&data2->lock);
145 __raw_spin_lock(&data1->lock);
149 u64 sched_clock_cpu(int cpu)
151 struct sched_clock_data *scd = cpu_sdc(cpu);
154 if (unlikely(!sched_clock_running))
157 WARN_ON_ONCE(!irqs_disabled());
160 if (cpu != raw_smp_processor_id()) {
162 * in order to update a remote cpu's clock based on our
163 * unstable raw time rebase it against:
164 * tick_raw (offset between raw counters)
165 * tick_gotd (tick offset between cpus)
167 struct sched_clock_data *my_scd = this_scd();
169 lock_double_clock(scd, my_scd);
171 now += scd->tick_raw - my_scd->tick_raw;
172 now += my_scd->tick_gtod - scd->tick_gtod;
174 __raw_spin_unlock(&my_scd->lock);
176 __raw_spin_lock(&scd->lock);
179 clock = __update_sched_clock(scd, now);
181 __raw_spin_unlock(&scd->lock);
186 void sched_clock_tick(void)
188 struct sched_clock_data *scd = this_scd();
191 if (unlikely(!sched_clock_running))
194 WARN_ON_ONCE(!irqs_disabled());
196 now_gtod = ktime_to_ns(ktime_get());
199 __raw_spin_lock(&scd->lock);
200 __update_sched_clock(scd, now);
202 * update tick_gtod after __update_sched_clock() because that will
203 * already observe 1 new jiffy; adding a new tick_gtod to that would
204 * increase the clock 2 jiffies.
207 scd->tick_gtod = now_gtod;
208 __raw_spin_unlock(&scd->lock);
212 * We are going deep-idle (irqs are disabled):
214 void sched_clock_idle_sleep_event(void)
216 sched_clock_cpu(smp_processor_id());
218 EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
221 * We just idled delta nanoseconds (called with irqs disabled):
223 void sched_clock_idle_wakeup_event(u64 delta_ns)
225 struct sched_clock_data *scd = this_scd();
226 u64 now = sched_clock();
229 * Override the previous timestamp and ignore all
230 * sched_clock() deltas that occured while we idled,
231 * and use the PM-provided delta_ns to advance the
234 __raw_spin_lock(&scd->lock);
235 scd->clock += delta_ns;
236 __raw_spin_unlock(&scd->lock);
238 touch_softlockup_watchdog();
240 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
244 unsigned long long cpu_clock(int cpu)
246 unsigned long long clock;
249 local_irq_save(flags);
250 clock = sched_clock_cpu(cpu);
251 local_irq_restore(flags);
255 EXPORT_SYMBOL_GPL(cpu_clock);