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 u32 __read_mostly (*read_sched_clock_32)(void);
  53
  54 static u64 notrace read_sched_clock_32_wrapper(void)
  55 {
  56         return read_sched_clock_32();
  57 }
  58
  59 static u64 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
  60
  61 static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
  62 {
  63         return (cyc * mult) >> shift;
  64 }
  65
  66 unsigned long long notrace sched_clock(void)
  67 {
  68         u64 epoch_ns;
  69         u64 epoch_cyc;
  70         u64 cyc;
  71         unsigned long seq;
  72
  73         if (cd.suspended)
  74                 return cd.epoch_ns;
  75
  76         do {
  77                 seq = raw_read_seqcount_begin(&cd.seq);
  78                 epoch_cyc = cd.epoch_cyc;
  79                 epoch_ns = cd.epoch_ns;
  80         } while (read_seqcount_retry(&cd.seq, seq));
  81
  82         cyc = read_sched_clock();
  83         cyc = (cyc - epoch_cyc) & sched_clock_mask;
  84         return epoch_ns + cyc_to_ns(cyc, cd.mult, cd.shift);
  85 }
  86
  87 /*
  88  * Atomically update the sched_clock epoch.
  89  */
  90 static void notrace update_sched_clock(void)
  91 {
  92         unsigned long flags;
  93         u64 cyc;
  94         u64 ns;
  95
  96         cyc = read_sched_clock();
  97         ns = cd.epoch_ns +
  98                 cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
  99                           cd.mult, cd.shift);
 100
 101         raw_local_irq_save(flags);
 102         raw_write_seqcount_begin(&cd.seq);
 103         cd.epoch_ns = ns;
 104         cd.epoch_cyc = cyc;
 105         raw_write_seqcount_end(&cd.seq);
 106         raw_local_irq_restore(flags);
 107 }
 108
 109 static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
 110 {
 111         update_sched_clock();
 112         hrtimer_forward_now(hrt, cd.wrap_kt);
 113         return HRTIMER_RESTART;
 114 }
 115
 116 void __init sched_clock_register(u64 (*read)(void), int bits,
 117                                  unsigned long rate)
 118 {
 119         unsigned long r;
 120         u64 res, wrap;
 121         char r_unit;
 122
 123         if (cd.rate > rate)
 124                 return;
 125
 126         WARN_ON(!irqs_disabled());
 127         read_sched_clock = read;
 128         sched_clock_mask = CLOCKSOURCE_MASK(bits);
 129         cd.rate = rate;
 130
 131         /* calculate the mult/shift to convert counter ticks to ns. */
 132         clocks_calc_mult_shift(&cd.mult, &cd.shift, rate, NSEC_PER_SEC, 3600);
 133
 134         r = rate;
 135         if (r >= 4000000) {
 136                 r /= 1000000;
 137                 r_unit = 'M';
 138         } else if (r >= 1000) {
 139                 r /= 1000;
 140                 r_unit = 'k';
 141         } else
 142                 r_unit = ' ';
 143
 144         /* calculate how many ns until we wrap */
 145         wrap = clocks_calc_max_nsecs(cd.mult, cd.shift, 0, sched_clock_mask);
 146         cd.wrap_kt = ns_to_ktime(wrap - (wrap >> 3));
 147
 148         /* calculate the ns resolution of this counter */
 149         res = cyc_to_ns(1ULL, cd.mult, cd.shift);
 150         pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
 151                 bits, r, r_unit, res, wrap);
 152
 153         update_sched_clock();
 154
 155         /*
 156          * Ensure that sched_clock() starts off at 0ns
 157          */
 158         cd.epoch_ns = 0;
 159
 160         /* Enable IRQ time accounting if we have a fast enough sched_clock */
 161         if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
 162                 enable_sched_clock_irqtime();
 163
 164         pr_debug("Registered %pF as sched_clock source\n", read);
 165 }
 166
 167 void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
 168 {
 169         read_sched_clock_32 = read;
 170         sched_clock_register(read_sched_clock_32_wrapper, bits, rate);
 171 }
 172
 173 void __init sched_clock_postinit(void)
 174 {
 175         /*
 176          * If no sched_clock function has been provided at that point,
 177          * make it the final one one.
 178          */
 179         if (read_sched_clock == jiffy_sched_clock_read)
 180                 sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
 181
 182         update_sched_clock();
 183
 184         /*
 185          * Start the timer to keep sched_clock() properly updated and
 186          * sets the initial epoch.
 187          */
 188         hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 189         sched_clock_timer.function = sched_clock_poll;
 190         hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
 191 }
 192
 193 static int sched_clock_suspend(void)
 194 {
 195         sched_clock_poll(&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         cd.suspended = false;
 204 }
 205
 206 static struct syscore_ops sched_clock_ops = {
 207         .suspend = sched_clock_suspend,
 208         .resume = sched_clock_resume,
 209 };
 210
 211 static int __init sched_clock_syscore_init(void)
 212 {
 213         register_syscore_ops(&sched_clock_ops);
 214         return 0;
 215 }
 216 device_initcall(sched_clock_syscore_init);