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:
16 * - explicit idle events
18 * We use gtod as base and the unstable clock deltas. The deltas are filtered,
19 * making it monotonic and keeping it within an expected window.
21 * Furthermore, explicit sleep and wakeup hooks allow us to account for time
22 * that is otherwise invisible (TSC gets stopped).
24 * The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
25 * consistent between cpus (never more than 2 jiffies difference).
27 #include <linux/sched.h>
28 #include <linux/percpu.h>
29 #include <linux/spinlock.h>
30 #include <linux/ktime.h>
31 #include <linux/module.h>
34 * Scheduler clock - returns current time in nanosec units.
35 * This is default implementation.
36 * Architectures and sub-architectures can override this.
38 unsigned long long __attribute__((weak)) sched_clock(void)
40 return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
43 static __read_mostly int sched_clock_running;
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.
60 static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
62 static inline struct sched_clock_data *this_scd(void)
64 return &__get_cpu_var(sched_clock_data);
67 static inline struct sched_clock_data *cpu_sdc(int cpu)
69 return &per_cpu(sched_clock_data, cpu);
72 void sched_clock_init(void)
74 u64 ktime_now = ktime_to_ns(ktime_get());
77 for_each_possible_cpu(cpu) {
78 struct sched_clock_data *scd = cpu_sdc(cpu);
80 scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
82 scd->tick_gtod = ktime_now;
83 scd->clock = ktime_now;
86 sched_clock_running = 1;
90 * min,max except they take wrapping into account
93 static inline u64 wrap_min(u64 x, u64 y)
95 return (s64)(x - y) < 0 ? x : y;
98 static inline u64 wrap_max(u64 x, u64 y)
100 return (s64)(x - y) > 0 ? x : y;
104 * update the percpu scd from the raw @now value
106 * - filter out backward motion
107 * - use the GTOD tick value to create a window to filter crazy TSC values
109 static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
111 s64 delta = now - scd->tick_raw;
112 u64 clock, min_clock, max_clock;
114 WARN_ON_ONCE(!irqs_disabled());
116 if (unlikely(delta < 0))
120 * scd->clock = clamp(scd->tick_gtod + delta,
121 * max(scd->tick_gtod, scd->clock),
122 * scd->tick_gtod + TICK_NSEC);
125 clock = scd->tick_gtod + delta;
126 min_clock = wrap_max(scd->tick_gtod, scd->clock);
127 max_clock = scd->tick_gtod + TICK_NSEC;
129 clock = wrap_max(clock, min_clock);
130 clock = wrap_min(clock, max_clock);
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);
152 u64 now, clock, this_clock, remote_clock;
154 if (unlikely(!sched_clock_running))
157 WARN_ON_ONCE(!irqs_disabled());
160 if (cpu != raw_smp_processor_id()) {
161 struct sched_clock_data *my_scd = this_scd();
163 lock_double_clock(scd, my_scd);
165 this_clock = __update_sched_clock(my_scd, now);
166 remote_clock = scd->clock;
169 * Use the opportunity that we have both locks
170 * taken to couple the two clocks: we take the
171 * larger time as the latest time for both
172 * runqueues. (this creates monotonic movement)
174 if (likely((s64)(remote_clock - this_clock) < 0)) {
179 * Should be rare, but possible:
181 clock = remote_clock;
182 my_scd->clock = remote_clock;
185 __raw_spin_unlock(&my_scd->lock);
187 __raw_spin_lock(&scd->lock);
188 clock = __update_sched_clock(scd, now);
191 __raw_spin_unlock(&scd->lock);
196 void sched_clock_tick(void)
198 struct sched_clock_data *scd = this_scd();
201 if (unlikely(!sched_clock_running))
204 WARN_ON_ONCE(!irqs_disabled());
206 now_gtod = ktime_to_ns(ktime_get());
209 __raw_spin_lock(&scd->lock);
211 scd->tick_gtod = now_gtod;
212 __update_sched_clock(scd, now);
213 __raw_spin_unlock(&scd->lock);
217 * We are going deep-idle (irqs are disabled):
219 void sched_clock_idle_sleep_event(void)
221 sched_clock_cpu(smp_processor_id());
223 EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
226 * We just idled delta nanoseconds (called with irqs disabled):
228 void sched_clock_idle_wakeup_event(u64 delta_ns)
231 touch_softlockup_watchdog();
233 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
235 #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
237 void sched_clock_init(void)
239 sched_clock_running = 1;
242 u64 sched_clock_cpu(int cpu)
244 if (unlikely(!sched_clock_running))
247 return sched_clock();
252 unsigned long long cpu_clock(int cpu)
254 unsigned long long clock;
257 local_irq_save(flags);
258 clock = sched_clock_cpu(cpu);
259 local_irq_restore(flags);
263 EXPORT_SYMBOL_GPL(cpu_clock);