kernel/sched_clock.c

   1 /*
   2  * sched_clock for unstable cpu clocks
   3  *
   4  *  Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
   5  *
   6  *  Updates and enhancements:
   7  *    Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
   8  *
   9  * Based on code by:
  10  *   Ingo Molnar <mingo@redhat.com>
  11  *   Guillaume Chazarain <guichaz@gmail.com>
  12  *
  13  * Create a semi stable clock from a mixture of other events, including:
  14  *  - gtod
  15  *  - sched_clock()
  16  *  - explicit idle events
  17  *
  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.
  20  *
  21  * Furthermore, explicit sleep and wakeup hooks allow us to account for time
  22  * that is otherwise invisible (TSC gets stopped).
  23  *
  24  * The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
  25  * consistent between cpus (never more than 2 jiffies difference).
  26  */
  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>
  33
  34 /*
  35  * Scheduler clock - returns current time in nanosec units.
  36  * This is default implementation.
  37  * Architectures and sub-architectures can override this.
  38  */
  39 unsigned long long __attribute__((weak)) sched_clock(void)
  40 {
  41         return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
  42 }
  43
  44 static __read_mostly int sched_clock_running;
  45
  46 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
  47 __read_mostly int sched_clock_stable;
  48
  49 struct sched_clock_data {
  50         /*
  51          * Raw spinlock - this is a special case: this might be called
  52          * from within instrumentation code so we dont want to do any
  53          * instrumentation ourselves.
  54          */
  55         raw_spinlock_t          lock;
  56
  57         u64                     tick_raw;
  58         u64                     tick_gtod;
  59         u64                     clock;
  60 };
  61
  62 static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
  63
  64 static inline struct sched_clock_data *this_scd(void)
  65 {
  66         return &__get_cpu_var(sched_clock_data);
  67 }
  68
  69 static inline struct sched_clock_data *cpu_sdc(int cpu)
  70 {
  71         return &per_cpu(sched_clock_data, cpu);
  72 }
  73
  74 void sched_clock_init(void)
  75 {
  76         u64 ktime_now = ktime_to_ns(ktime_get());
  77         int cpu;
  78
  79         for_each_possible_cpu(cpu) {
  80                 struct sched_clock_data *scd = cpu_sdc(cpu);
  81
  82                 scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
  83                 scd->tick_raw = 0;
  84                 scd->tick_gtod = ktime_now;
  85                 scd->clock = ktime_now;
  86         }
  87
  88         sched_clock_running = 1;
  89 }
  90
  91 /*
  92  * min, max except they take wrapping into account
  93  */
  94
  95 static inline u64 wrap_min(u64 x, u64 y)
  96 {
  97         return (s64)(x - y) < 0 ? x : y;
  98 }
  99
 100 static inline u64 wrap_max(u64 x, u64 y)
 101 {
 102         return (s64)(x - y) > 0 ? x : y;
 103 }
 104
 105 /*
 106  * update the percpu scd from the raw @now value
 107  *
 108  *  - filter out backward motion
 109  *  - use the GTOD tick value to create a window to filter crazy TSC values
 110  */
 111 static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
 112 {
 113         s64 delta = now - scd->tick_raw;
 114         u64 clock, min_clock, max_clock;
 115
 116         if (unlikely(delta < 0))
 117                 delta = 0;
 118
 119         /*
 120          * scd->clock = clamp(scd->tick_gtod + delta,
 121          *                    max(scd->tick_gtod, scd->clock),
 122          *                    scd->tick_gtod + TICK_NSEC);
 123          */
 124
 125         clock = scd->tick_gtod + delta;
 126         min_clock = wrap_max(scd->tick_gtod, scd->clock);
 127         max_clock = wrap_max(scd->clock, scd->tick_gtod + TICK_NSEC);
 128
 129         clock = wrap_max(clock, min_clock);
 130         clock = wrap_min(clock, max_clock);
 131
 132         scd->clock = clock;
 133
 134         return scd->clock;
 135 }
 136
 137 static void lock_double_clock(struct sched_clock_data *data1,
 138                                 struct sched_clock_data *data2)
 139 {
 140         if (data1 < data2) {
 141                 __raw_spin_lock(&data1->lock);
 142                 __raw_spin_lock(&data2->lock);
 143         } else {
 144                 __raw_spin_lock(&data2->lock);
 145                 __raw_spin_lock(&data1->lock);
 146         }
 147 }
 148
 149 u64 sched_clock_cpu(int cpu)
 150 {
 151         u64 now, clock, this_clock, remote_clock;
 152         struct sched_clock_data *scd;
 153
 154         if (sched_clock_stable)
 155                 return sched_clock();
 156
 157         scd = cpu_sdc(cpu);
 158
 159         /*
 160          * Normally this is not called in NMI context - but if it is,
 161          * trying to do any locking here is totally lethal.
 162          */
 163         if (unlikely(in_nmi()))
 164                 return scd->clock;
 165
 166         if (unlikely(!sched_clock_running))
 167                 return 0ull;
 168
 169         WARN_ON_ONCE(!irqs_disabled());
 170         now = sched_clock();
 171
 172         if (cpu != raw_smp_processor_id()) {
 173                 struct sched_clock_data *my_scd = this_scd();
 174
 175                 lock_double_clock(scd, my_scd);
 176
 177                 this_clock = __update_sched_clock(my_scd, now);
 178                 remote_clock = scd->clock;
 179
 180                 /*
 181                  * Use the opportunity that we have both locks
 182                  * taken to couple the two clocks: we take the
 183                  * larger time as the latest time for both
 184                  * runqueues. (this creates monotonic movement)
 185                  */
 186                 if (likely((s64)(remote_clock - this_clock) < 0)) {
 187                         clock = this_clock;
 188                         scd->clock = clock;
 189                 } else {
 190                         /*
 191                          * Should be rare, but possible:
 192                          */
 193                         clock = remote_clock;
 194                         my_scd->clock = remote_clock;
 195                 }
 196
 197                 __raw_spin_unlock(&my_scd->lock);
 198         } else {
 199                 __raw_spin_lock(&scd->lock);
 200                 clock = __update_sched_clock(scd, now);
 201         }
 202
 203         __raw_spin_unlock(&scd->lock);
 204
 205         return clock;
 206 }
 207
 208 void sched_clock_tick(void)
 209 {
 210         struct sched_clock_data *scd;
 211         u64 now, now_gtod;
 212
 213         if (sched_clock_stable)
 214                 return;
 215
 216         if (unlikely(!sched_clock_running))
 217                 return;
 218
 219         WARN_ON_ONCE(!irqs_disabled());
 220
 221         scd = this_scd();
 222         now_gtod = ktime_to_ns(ktime_get());
 223         now = sched_clock();
 224
 225         __raw_spin_lock(&scd->lock);
 226         scd->tick_raw = now;
 227         scd->tick_gtod = now_gtod;
 228         __update_sched_clock(scd, now);
 229         __raw_spin_unlock(&scd->lock);
 230 }
 231
 232 /*
 233  * We are going deep-idle (irqs are disabled):
 234  */
 235 void sched_clock_idle_sleep_event(void)
 236 {
 237         sched_clock_cpu(smp_processor_id());
 238 }
 239 EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
 240
 241 /*
 242  * We just idled delta nanoseconds (called with irqs disabled):
 243  */
 244 void sched_clock_idle_wakeup_event(u64 delta_ns)
 245 {
 246         if (timekeeping_suspended)
 247                 return;
 248
 249         sched_clock_tick();
 250         touch_softlockup_watchdog();
 251 }
 252 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
 253
 254 #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
 255
 256 void sched_clock_init(void)
 257 {
 258         sched_clock_running = 1;
 259 }
 260
 261 u64 sched_clock_cpu(int cpu)
 262 {
 263         if (unlikely(!sched_clock_running))
 264                 return 0;
 265
 266         return sched_clock();
 267 }
 268
 269 #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
 270
 271 unsigned long long cpu_clock(int cpu)
 272 {
 273         unsigned long long clock;
 274         unsigned long flags;
 275
 276         local_irq_save(flags);
 277         clock = sched_clock_cpu(cpu);
 278         local_irq_restore(flags);
 279
 280         return clock;
 281 }
 282 EXPORT_SYMBOL_GPL(cpu_clock);