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  * Based on code by:
   7  *   Ingo Molnar <mingo@redhat.com>
   8  *   Guillaume Chazarain <guichaz@gmail.com>
   9  *
  10  * Create a semi stable clock from a mixture of other events, including:
  11  *  - gtod
  12  *  - jiffies
  13  *  - sched_clock()
  14  *  - explicit idle events
  15  *
  16  * We use gtod as base and the unstable clock deltas. The deltas are filtered,
  17  * making it monotonic and keeping it within an expected window.  This window
  18  * is set up using jiffies.
  19  *
  20  * Furthermore, explicit sleep and wakeup hooks allow us to account for time
  21  * that is otherwise invisible (TSC gets stopped).
  22  *
  23  * The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
  24  * consistent between cpus (never more than 1 jiffies difference).
  25  */
  26 #include <linux/sched.h>
  27 #include <linux/percpu.h>
  28 #include <linux/spinlock.h>
  29 #include <linux/ktime.h>
  30 #include <linux/module.h>
  31
  32
  33 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
  34
  35 struct sched_clock_data {
  36         /*
  37          * Raw spinlock - this is a special case: this might be called
  38          * from within instrumentation code so we dont want to do any
  39          * instrumentation ourselves.
  40          */
  41         raw_spinlock_t          lock;
  42
  43         unsigned long           prev_jiffies;
  44         u64                     prev_raw;
  45         u64                     tick_raw;
  46         u64                     tick_gtod;
  47         u64                     clock;
  48 };
  49
  50 static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
  51
  52 static inline struct sched_clock_data *this_scd(void)
  53 {
  54         return &__get_cpu_var(sched_clock_data);
  55 }
  56
  57 static inline struct sched_clock_data *cpu_sdc(int cpu)
  58 {
  59         return &per_cpu(sched_clock_data, cpu);
  60 }
  61
  62 static __read_mostly int sched_clock_running;
  63
  64 void sched_clock_init(void)
  65 {
  66         u64 ktime_now = ktime_to_ns(ktime_get());
  67         unsigned long now_jiffies = jiffies;
  68         int cpu;
  69
  70         for_each_possible_cpu(cpu) {
  71                 struct sched_clock_data *scd = cpu_sdc(cpu);
  72
  73                 scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
  74                 scd->prev_jiffies = now_jiffies;
  75                 scd->prev_raw = 0;
  76                 scd->tick_raw = 0;
  77                 scd->tick_gtod = ktime_now;
  78                 scd->clock = ktime_now;
  79         }
  80
  81         sched_clock_running = 1;
  82 }
  83
  84 /*
  85  * update the percpu scd from the raw @now value
  86  *
  87  *  - filter out backward motion
  88  *  - use jiffies to generate a min,max window to clip the raw values
  89  */
  90 static void __update_sched_clock(struct sched_clock_data *scd, u64 now)
  91 {
  92         unsigned long now_jiffies = jiffies;
  93         long delta_jiffies = now_jiffies - scd->prev_jiffies;
  94         u64 clock = scd->clock;
  95         u64 min_clock, max_clock;
  96         s64 delta = now - scd->prev_raw;
  97
  98         WARN_ON_ONCE(!irqs_disabled());
  99         min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC;
 100
 101         if (unlikely(delta < 0)) {
 102                 clock++;
 103                 goto out;
 104         }
 105
 106         max_clock = min_clock + TICK_NSEC;
 107
 108         if (unlikely(clock + delta > max_clock)) {
 109                 if (clock < max_clock)
 110                         clock = max_clock;
 111                 else
 112                         clock++;
 113         } else {
 114                 clock += delta;
 115         }
 116
 117  out:
 118         if (unlikely(clock < min_clock))
 119                 clock = min_clock;
 120
 121         scd->prev_raw = now;
 122         scd->prev_jiffies = now_jiffies;
 123         scd->clock = clock;
 124 }
 125
 126 static void lock_double_clock(struct sched_clock_data *data1,
 127                                 struct sched_clock_data *data2)
 128 {
 129         if (data1 < data2) {
 130                 __raw_spin_lock(&data1->lock);
 131                 __raw_spin_lock(&data2->lock);
 132         } else {
 133                 __raw_spin_lock(&data2->lock);
 134                 __raw_spin_lock(&data1->lock);
 135         }
 136 }
 137
 138 u64 sched_clock_cpu(int cpu)
 139 {
 140         struct sched_clock_data *scd = cpu_sdc(cpu);
 141         u64 now, clock;
 142
 143         if (unlikely(!sched_clock_running))
 144                 return 0ull;
 145
 146         WARN_ON_ONCE(!irqs_disabled());
 147         now = sched_clock();
 148
 149         if (cpu != raw_smp_processor_id()) {
 150                 /*
 151                  * in order to update a remote cpu's clock based on our
 152                  * unstable raw time rebase it against:
 153                  *   tick_raw           (offset between raw counters)
 154                  *   tick_gotd          (tick offset between cpus)
 155                  */
 156                 struct sched_clock_data *my_scd = this_scd();
 157
 158                 lock_double_clock(scd, my_scd);
 159
 160                 now -= my_scd->tick_raw;
 161                 now += scd->tick_raw;
 162
 163                 now -= my_scd->tick_gtod;
 164                 now += scd->tick_gtod;
 165
 166                 __raw_spin_unlock(&my_scd->lock);
 167         } else {
 168                 __raw_spin_lock(&scd->lock);
 169         }
 170
 171         __update_sched_clock(scd, now);
 172         clock = scd->clock;
 173
 174         __raw_spin_unlock(&scd->lock);
 175
 176         return clock;
 177 }
 178
 179 void sched_clock_tick(void)
 180 {
 181         struct sched_clock_data *scd = this_scd();
 182         u64 now, now_gtod;
 183
 184         if (unlikely(!sched_clock_running))
 185                 return;
 186
 187         WARN_ON_ONCE(!irqs_disabled());
 188
 189         now = sched_clock();
 190         now_gtod = ktime_to_ns(ktime_get());
 191
 192         __raw_spin_lock(&scd->lock);
 193         __update_sched_clock(scd, now);
 194         /*
 195          * update tick_gtod after __update_sched_clock() because that will
 196          * already observe 1 new jiffy; adding a new tick_gtod to that would
 197          * increase the clock 2 jiffies.
 198          */
 199         scd->tick_raw = now;
 200         scd->tick_gtod = now_gtod;
 201         __raw_spin_unlock(&scd->lock);
 202 }
 203
 204 /*
 205  * We are going deep-idle (irqs are disabled):
 206  */
 207 void sched_clock_idle_sleep_event(void)
 208 {
 209         sched_clock_cpu(smp_processor_id());
 210 }
 211 EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
 212
 213 /*
 214  * We just idled delta nanoseconds (called with irqs disabled):
 215  */
 216 void sched_clock_idle_wakeup_event(u64 delta_ns)
 217 {
 218         struct sched_clock_data *scd = this_scd();
 219         u64 now = sched_clock();
 220
 221         /*
 222          * Override the previous timestamp and ignore all
 223          * sched_clock() deltas that occured while we idled,
 224          * and use the PM-provided delta_ns to advance the
 225          * rq clock:
 226          */
 227         __raw_spin_lock(&scd->lock);
 228         scd->prev_raw = now;
 229         scd->clock += delta_ns;
 230         __raw_spin_unlock(&scd->lock);
 231
 232         touch_softlockup_watchdog();
 233 }
 234 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
 235
 236 #endif
 237
 238 /*
 239  * Scheduler clock - returns current time in nanosec units.
 240  * This is default implementation.
 241  * Architectures and sub-architectures can override this.
 242  */
 243 unsigned long long __attribute__((weak)) sched_clock(void)
 244 {
 245         return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
 246 }