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 void sched_clock_init(void)
  63 {
  64         u64 ktime_now = ktime_to_ns(ktime_get());
  65         u64 now = 0;
  66         int cpu;
  67
  68         for_each_possible_cpu(cpu) {
  69                 struct sched_clock_data *scd = cpu_sdc(cpu);
  70
  71                 scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
  72                 scd->prev_jiffies = jiffies;
  73                 scd->prev_raw = now;
  74                 scd->tick_raw = now;
  75                 scd->tick_gtod = ktime_now;
  76                 scd->clock = ktime_now;
  77         }
  78 }
  79
  80 /*
  81  * update the percpu scd from the raw @now value
  82  *
  83  *  - filter out backward motion
  84  *  - use jiffies to generate a min,max window to clip the raw values
  85  */
  86 static void __update_sched_clock(struct sched_clock_data *scd, u64 now)
  87 {
  88         unsigned long now_jiffies = jiffies;
  89         long delta_jiffies = now_jiffies - scd->prev_jiffies;
  90         u64 clock = scd->clock;
  91         u64 min_clock, max_clock;
  92         s64 delta = now - scd->prev_raw;
  93
  94         WARN_ON_ONCE(!irqs_disabled());
  95         min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC;
  96
  97         if (unlikely(delta < 0)) {
  98                 clock++;
  99                 goto out;
 100         }
 101
 102         max_clock = min_clock + TICK_NSEC;
 103
 104         if (unlikely(clock + delta > max_clock)) {
 105                 if (clock < max_clock)
 106                         clock = max_clock;
 107                 else
 108                         clock++;
 109         } else {
 110                 clock += delta;
 111         }
 112
 113  out:
 114         if (unlikely(clock < min_clock))
 115                 clock = min_clock;
 116
 117         scd->prev_raw = now;
 118         scd->prev_jiffies = now_jiffies;
 119         scd->clock = clock;
 120 }
 121
 122 static void lock_double_clock(struct sched_clock_data *data1,
 123                                 struct sched_clock_data *data2)
 124 {
 125         if (data1 < data2) {
 126                 __raw_spin_lock(&data1->lock);
 127                 __raw_spin_lock(&data2->lock);
 128         } else {
 129                 __raw_spin_lock(&data2->lock);
 130                 __raw_spin_lock(&data1->lock);
 131         }
 132 }
 133
 134 u64 sched_clock_cpu(int cpu)
 135 {
 136         struct sched_clock_data *scd = cpu_sdc(cpu);
 137         u64 now, clock;
 138
 139         WARN_ON_ONCE(!irqs_disabled());
 140         now = sched_clock();
 141
 142         if (cpu != raw_smp_processor_id()) {
 143                 /*
 144                  * in order to update a remote cpu's clock based on our
 145                  * unstable raw time rebase it against:
 146                  *   tick_raw           (offset between raw counters)
 147                  *   tick_gotd          (tick offset between cpus)
 148                  */
 149                 struct sched_clock_data *my_scd = this_scd();
 150
 151                 lock_double_clock(scd, my_scd);
 152
 153                 now -= my_scd->tick_raw;
 154                 now += scd->tick_raw;
 155
 156                 now -= my_scd->tick_gtod;
 157                 now += scd->tick_gtod;
 158
 159                 __raw_spin_unlock(&my_scd->lock);
 160         } else {
 161                 __raw_spin_lock(&scd->lock);
 162         }
 163
 164         __update_sched_clock(scd, now);
 165         clock = scd->clock;
 166
 167         __raw_spin_unlock(&scd->lock);
 168
 169         return clock;
 170 }
 171
 172 void sched_clock_tick(void)
 173 {
 174         struct sched_clock_data *scd = this_scd();
 175         u64 now, now_gtod;
 176
 177         WARN_ON_ONCE(!irqs_disabled());
 178
 179         now = sched_clock();
 180         now_gtod = ktime_to_ns(ktime_get());
 181
 182         __raw_spin_lock(&scd->lock);
 183         __update_sched_clock(scd, now);
 184         /*
 185          * update tick_gtod after __update_sched_clock() because that will
 186          * already observe 1 new jiffy; adding a new tick_gtod to that would
 187          * increase the clock 2 jiffies.
 188          */
 189         scd->tick_raw = now;
 190         scd->tick_gtod = now_gtod;
 191         __raw_spin_unlock(&scd->lock);
 192 }
 193
 194 /*
 195  * We are going deep-idle (irqs are disabled):
 196  */
 197 void sched_clock_idle_sleep_event(void)
 198 {
 199         sched_clock_cpu(smp_processor_id());
 200 }
 201 EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
 202
 203 /*
 204  * We just idled delta nanoseconds (called with irqs disabled):
 205  */
 206 void sched_clock_idle_wakeup_event(u64 delta_ns)
 207 {
 208         struct sched_clock_data *scd = this_scd();
 209         u64 now = sched_clock();
 210
 211         /*
 212          * Override the previous timestamp and ignore all
 213          * sched_clock() deltas that occured while we idled,
 214          * and use the PM-provided delta_ns to advance the
 215          * rq clock:
 216          */
 217         __raw_spin_lock(&scd->lock);
 218         scd->prev_raw = now;
 219         scd->clock += delta_ns;
 220         __raw_spin_unlock(&scd->lock);
 221
 222         touch_softlockup_watchdog();
 223 }
 224 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
 225
 226 #endif
 227
 228 /*
 229  * Scheduler clock - returns current time in nanosec units.
 230  * This is default implementation.
 231  * Architectures and sub-architectures can override this.
 232  */
 233 unsigned long long __attribute__((weak)) sched_clock(void)
 234 {
 235         return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
 236 }