Linux 2.6.33-rc6
[cris-mirror.git] / kernel / sched_clock.c
blob5b496132c28a1baca2a6353c6a6b0216a0f02508
1 /*
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>
9 * Based on code by:
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:
14 * - gtod
15 * - sched_clock()
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/spinlock.h>
28 #include <linux/hardirq.h>
29 #include <linux/module.h>
30 #include <linux/percpu.h>
31 #include <linux/ktime.h>
32 #include <linux/sched.h>
35 * Scheduler clock - returns current time in nanosec units.
36 * This is default implementation.
37 * Architectures and sub-architectures can override this.
39 unsigned long long __attribute__((weak)) sched_clock(void)
41 return (unsigned long long)(jiffies - INITIAL_JIFFIES)
42 * (NSEC_PER_SEC / HZ);
45 static __read_mostly int sched_clock_running;
47 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
48 __read_mostly int sched_clock_stable;
50 struct sched_clock_data {
51 u64 tick_raw;
52 u64 tick_gtod;
53 u64 clock;
56 static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
58 static inline struct sched_clock_data *this_scd(void)
60 return &__get_cpu_var(sched_clock_data);
63 static inline struct sched_clock_data *cpu_sdc(int cpu)
65 return &per_cpu(sched_clock_data, cpu);
68 void sched_clock_init(void)
70 u64 ktime_now = ktime_to_ns(ktime_get());
71 int cpu;
73 for_each_possible_cpu(cpu) {
74 struct sched_clock_data *scd = cpu_sdc(cpu);
76 scd->tick_raw = 0;
77 scd->tick_gtod = ktime_now;
78 scd->clock = ktime_now;
81 sched_clock_running = 1;
85 * min, max except they take wrapping into account
88 static inline u64 wrap_min(u64 x, u64 y)
90 return (s64)(x - y) < 0 ? x : y;
93 static inline u64 wrap_max(u64 x, u64 y)
95 return (s64)(x - y) > 0 ? x : y;
99 * update the percpu scd from the raw @now value
101 * - filter out backward motion
102 * - use the GTOD tick value to create a window to filter crazy TSC values
104 static u64 sched_clock_local(struct sched_clock_data *scd)
106 u64 now, clock, old_clock, min_clock, max_clock;
107 s64 delta;
109 again:
110 now = sched_clock();
111 delta = now - scd->tick_raw;
112 if (unlikely(delta < 0))
113 delta = 0;
115 old_clock = scd->clock;
118 * scd->clock = clamp(scd->tick_gtod + delta,
119 * max(scd->tick_gtod, scd->clock),
120 * scd->tick_gtod + TICK_NSEC);
123 clock = scd->tick_gtod + delta;
124 min_clock = wrap_max(scd->tick_gtod, old_clock);
125 max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
127 clock = wrap_max(clock, min_clock);
128 clock = wrap_min(clock, max_clock);
130 if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
131 goto again;
133 return clock;
136 static u64 sched_clock_remote(struct sched_clock_data *scd)
138 struct sched_clock_data *my_scd = this_scd();
139 u64 this_clock, remote_clock;
140 u64 *ptr, old_val, val;
142 sched_clock_local(my_scd);
143 again:
144 this_clock = my_scd->clock;
145 remote_clock = scd->clock;
148 * Use the opportunity that we have both locks
149 * taken to couple the two clocks: we take the
150 * larger time as the latest time for both
151 * runqueues. (this creates monotonic movement)
153 if (likely((s64)(remote_clock - this_clock) < 0)) {
154 ptr = &scd->clock;
155 old_val = remote_clock;
156 val = this_clock;
157 } else {
159 * Should be rare, but possible:
161 ptr = &my_scd->clock;
162 old_val = this_clock;
163 val = remote_clock;
166 if (cmpxchg64(ptr, old_val, val) != old_val)
167 goto again;
169 return val;
172 u64 sched_clock_cpu(int cpu)
174 struct sched_clock_data *scd;
175 u64 clock;
177 WARN_ON_ONCE(!irqs_disabled());
179 if (sched_clock_stable)
180 return sched_clock();
182 if (unlikely(!sched_clock_running))
183 return 0ull;
185 scd = cpu_sdc(cpu);
187 if (cpu != smp_processor_id())
188 clock = sched_clock_remote(scd);
189 else
190 clock = sched_clock_local(scd);
192 return clock;
195 void sched_clock_tick(void)
197 struct sched_clock_data *scd;
198 u64 now, now_gtod;
200 if (sched_clock_stable)
201 return;
203 if (unlikely(!sched_clock_running))
204 return;
206 WARN_ON_ONCE(!irqs_disabled());
208 scd = this_scd();
209 now_gtod = ktime_to_ns(ktime_get());
210 now = sched_clock();
212 scd->tick_raw = now;
213 scd->tick_gtod = now_gtod;
214 sched_clock_local(scd);
218 * We are going deep-idle (irqs are disabled):
220 void sched_clock_idle_sleep_event(void)
222 sched_clock_cpu(smp_processor_id());
224 EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
227 * We just idled delta nanoseconds (called with irqs disabled):
229 void sched_clock_idle_wakeup_event(u64 delta_ns)
231 if (timekeeping_suspended)
232 return;
234 sched_clock_tick();
235 touch_softlockup_watchdog();
237 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
239 unsigned long long cpu_clock(int cpu)
241 unsigned long long clock;
242 unsigned long flags;
244 local_irq_save(flags);
245 clock = sched_clock_cpu(cpu);
246 local_irq_restore(flags);
248 return clock;
251 #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
253 void sched_clock_init(void)
255 sched_clock_running = 1;
258 u64 sched_clock_cpu(int cpu)
260 if (unlikely(!sched_clock_running))
261 return 0;
263 return sched_clock();
267 unsigned long long cpu_clock(int cpu)
269 return sched_clock_cpu(cpu);
272 #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
274 EXPORT_SYMBOL_GPL(cpu_clock);