kernel/time/sched_clock.c

   1 /*
   2  * sched_clock.c: support for extending counters to full 64-bit ns counter
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8 #include <linux/clocksource.h>
   9 #include <linux/init.h>
  10 #include <linux/jiffies.h>
  11 #include <linux/ktime.h>
  12 #include <linux/kernel.h>
  13 #include <linux/moduleparam.h>
  14 #include <linux/sched.h>
  15 #include <linux/syscore_ops.h>
  16 #include <linux/hrtimer.h>
  17 #include <linux/sched_clock.h>
  18 #include <linux/seqlock.h>
  19 #include <linux/bitops.h>
  20
  21 struct clock_data {
  22         ktime_t wrap_kt;
  23         u64 epoch_ns;
  24         u64 epoch_cyc;
  25         seqcount_t seq;
  26         unsigned long rate;
  27         u32 mult;
  28         u32 shift;
  29         bool suspended;
  30 };
  31
  32 static struct hrtimer sched_clock_timer;
  33 static int irqtime = -1;
  34
  35 core_param(irqtime, irqtime, int, 0400);
  36
  37 static struct clock_data cd = {
  38         .mult   = NSEC_PER_SEC / HZ,
  39 };
  40
  41 static u64 __read_mostly sched_clock_mask;
  42
  43 static u64 notrace jiffy_sched_clock_read(void)
  44 {
  45         /*
  46          * We don't need to use get_jiffies_64 on 32-bit arches here
  47          * because we register with BITS_PER_LONG
  48          */
  49         return (u64)(jiffies - INITIAL_JIFFIES);
  50 }
  51
  52 static u64 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
  53
  54 static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
  55 {
  56         return (cyc * mult) >> shift;
  57 }
  58
  59 unsigned long long notrace sched_clock(void)
  60 {
  61         u64 epoch_ns;
  62         u64 epoch_cyc;
  63         u64 cyc;
  64         unsigned long seq;
  65
  66         if (cd.suspended)
  67                 return cd.epoch_ns;
  68
  69         do {
  70                 seq = raw_read_seqcount_begin(&cd.seq);
  71                 epoch_cyc = cd.epoch_cyc;
  72                 epoch_ns = cd.epoch_ns;
  73         } while (read_seqcount_retry(&cd.seq, seq));
  74
  75         cyc = read_sched_clock();
  76         cyc = (cyc - epoch_cyc) & sched_clock_mask;
  77         return epoch_ns + cyc_to_ns(cyc, cd.mult, cd.shift);
  78 }
  79
  80 /*
  81  * Atomically update the sched_clock epoch.
  82  */
  83 static void notrace update_sched_clock(void)
  84 {
  85         unsigned long flags;
  86         u64 cyc;
  87         u64 ns;
  88
  89         cyc = read_sched_clock();
  90         ns = cd.epoch_ns +
  91                 cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
  92                           cd.mult, cd.shift);
  93
  94         raw_local_irq_save(flags);
  95         raw_write_seqcount_begin(&cd.seq);
  96         cd.epoch_ns = ns;
  97         cd.epoch_cyc = cyc;
  98         raw_write_seqcount_end(&cd.seq);
  99         raw_local_irq_restore(flags);
 100 }
 101
 102 static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
 103 {
 104         update_sched_clock();
 105         hrtimer_forward_now(hrt, cd.wrap_kt);
 106         return HRTIMER_RESTART;
 107 }
 108
 109 void __init sched_clock_register(u64 (*read)(void), int bits,
 110                                  unsigned long rate)
 111 {
 112         u64 res, wrap, new_mask, new_epoch, cyc, ns;
 113         u32 new_mult, new_shift;
 114         ktime_t new_wrap_kt;
 115         unsigned long r;
 116         char r_unit;
 117
 118         if (cd.rate > rate)
 119                 return;
 120
 121         WARN_ON(!irqs_disabled());
 122
 123         /* calculate the mult/shift to convert counter ticks to ns. */
 124         clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
 125
 126         new_mask = CLOCKSOURCE_MASK(bits);
 127
 128         /* calculate how many nanosecs until we risk wrapping */
 129         wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask);
 130         new_wrap_kt = ns_to_ktime(wrap);
 131
 132         /* update epoch for new counter and update epoch_ns from old counter*/
 133         new_epoch = read();
 134         cyc = read_sched_clock();
 135         ns = cd.epoch_ns + cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
 136                           cd.mult, cd.shift);
 137
 138         raw_write_seqcount_begin(&cd.seq);
 139         read_sched_clock = read;
 140         sched_clock_mask = new_mask;
 141         cd.rate = rate;
 142         cd.wrap_kt = new_wrap_kt;
 143         cd.mult = new_mult;
 144         cd.shift = new_shift;
 145         cd.epoch_cyc = new_epoch;
 146         cd.epoch_ns = ns;
 147         raw_write_seqcount_end(&cd.seq);
 148
 149         r = rate;
 150         if (r >= 4000000) {
 151                 r /= 1000000;
 152                 r_unit = 'M';
 153         } else if (r >= 1000) {
 154                 r /= 1000;
 155                 r_unit = 'k';
 156         } else
 157                 r_unit = ' ';
 158
 159         /* calculate the ns resolution of this counter */
 160         res = cyc_to_ns(1ULL, new_mult, new_shift);
 161
 162         pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
 163                 bits, r, r_unit, res, wrap);
 164
 165         /* Enable IRQ time accounting if we have a fast enough sched_clock */
 166         if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
 167                 enable_sched_clock_irqtime();
 168
 169         pr_debug("Registered %pF as sched_clock source\n", read);
 170 }
 171
 172 void __init sched_clock_postinit(void)
 173 {
 174         /*
 175          * If no sched_clock function has been provided at that point,
 176          * make it the final one one.
 177          */
 178         if (read_sched_clock == jiffy_sched_clock_read)
 179                 sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
 180
 181         update_sched_clock();
 182
 183         /*
 184          * Start the timer to keep sched_clock() properly updated and
 185          * sets the initial epoch.
 186          */
 187         hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 188         sched_clock_timer.function = sched_clock_poll;
 189         hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
 190 }
 191
 192 static int sched_clock_suspend(void)
 193 {
 194         update_sched_clock();
 195         hrtimer_cancel(&sched_clock_timer);
 196         cd.suspended = true;
 197         return 0;
 198 }
 199
 200 static void sched_clock_resume(void)
 201 {
 202         cd.epoch_cyc = read_sched_clock();
 203         hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
 204         cd.suspended = false;
 205 }
 206
 207 static struct syscore_ops sched_clock_ops = {
 208         .suspend = sched_clock_suspend,
 209         .resume = sched_clock_resume,
 210 };
 211
 212 static int __init sched_clock_syscore_init(void)
 213 {
 214         register_syscore_ops(&sched_clock_ops);
 215         return 0;
 216 }
 217 device_initcall(sched_clock_syscore_init);